Speciation: the Origin of Species
In the last fifty years, there has been an explosion of information about evolution and about human evolution in particular. But how does it all fit together? How can we bridge the immense historical gap between the australopithecines - who were simply bipedal apes - and the human race as it lives today? How can we reconcile our essentially animal identity with the our profound sense that as people, we are different from other animals? We are different, but what makes us different? And how does our evolution fit into the pattern of evolution in general?
The material is now there. Ernst Mayr's work on speciation has revolutionised evolutionary theory - though its implications, obscured by technical language, are not commonly known. More recently, some really excellent research on hominid prehistory has been done in particular areas. Books like Cohen's The Food Crisis in Prehistory (on the origins of agriculture) Keeley's War before Civilization (on tribal warfare) and Wrangham's Catching Fire (on fire and cooking) have changed our perceptions completely on their subject matter. These books and others have links to them on this site. But how does all the new material fit together into a coordinated picture? I have tried to fit it together on this site.
The site also includes some other material, including an account of speciation - the origin of species. This, in simplified language, is based almost entirely on Mayr's Population, Species and Evolution.
O ur ancestors were primates, accustomed to life in the trees. Nature provided them with four prehensile “hands” with fingers able to grip branches, rather than the paws, hooves or human feet of ground-dwelling mammals. They lived their lives in a friendly arboreal environment, where there was plenty of food and where predators could often be avoided by retreating to branches too thin to bear the weight of a big animal.
They were safest in forest so thick that they could search widely for food without coming down to the ground at all. Among our closest relatives the apes of the dense forests of South East Asia - orang-utans and gibbons - spend less time on the ground than gorillas and chimps, who live in the generally sparser forests of Africa. Only the strongest and heaviest of their fellow primates, mature male gorillas, are formidable enough to spend most of their time at ground level.
Yet somehow, starting five or six million years ago, two African primate groups - a group of monkeys and a group of apes - did manage to adapt to a life spent mostly away from the trees. The successful monkeys we call baboons. The successful apes - close relatives of our own ancestors - we now call Australopithecines.
Baboons are no ordinary primates. Baboons are monkeys; they can still climb well. But unlike other monkeys, baboons can also run fast on all fours like a dog.. Baboons resemble dogs also in the shape of their faces. The flat monkey face has become an elongated muzzle, containing (like a dog’s muzzle) powerful jaws equipped with strong muscles and sharp canine teeth. The jaws and teeth of a mature male baboon enable him to put up a reasonable defence even against a lion.
Baboons are a still a very successful group today. They show what can be done when Nature (or, if you prefer, Natural Selection) designs a successful terrestrial monkey. But Nature also designed a successful terrestrial ape.
The first successful ground-dwelling apes (we call them Australopithecines) adapted to life on the ground as successfully as the baboons, but in a very different way. Instead of becoming fast runners on all fours, they became slow bipeds. Instead of developing a great muzzle with powerful jaws and teeth, they had even flatter faces than their ape ancestors. Their canine teeth, far from getting bigger, became smaller, as if they were no longer needed for anything other than eating. Instead of improving their defences as the baboons had done, australopithecines seem at first glance to have made themselves defenceless.
Nevertheless they survived and flourished. How was it done? Darwin provides the only possible answer:
The free use of the arms and hands, partly the cause and partly the result of man’s erect posture, appears to have led in an indirect manner to other modifications of structure. The early male forefathers of man were, as previously stated, were probably furnished with great canine teeth; but as they gradually acquired the habit of using stones, clubs and other weapons for fighting with their enemies or rivals, they would use their jaws less and less. (The Descent of Man)
The australopithecines were true bipeds, undoubtedly at least as quick on their two feet as an active modern man. They had hands and arms which (not being required for running or walking on the ground) could afford to specialise in throwing and handling weapons and tools. They must have become expert at throwing stones; they would have been able to carry a supply of stones around with them, and they were probably also good at fighting at close quarters with natural clubs. As bipeds, able to keep predators at a safe distance much of the time with missiles and clubs, they must have had less need to run fast or to bite or threaten their enemies with their teeth. It was more useful for the canines to be adapted for eating.
Other plausible suggestions have been made to explain the evolutionary success of bipedal apes But curiously, all of them disregard defence against predators. Surely Darwin was right: bipedalism made it possible for the Australopithecines (and after them, our own ancestors) to “use stones, clubs and other weapons” to defend themselves and their young, rather than fighting with their teeth.
There is no definite evidence that australopithecines made artificial stone weapons (though they probably, like chimpanzees, made tools from softer materials). But unworked stones, well chosen and well thrown, make very good missiles anyway. The ability to throw stones (and to carry around with them a stock of suitable natural ammunition) would have given these animals a competitive advantage which no other animal had. They were much less vulnerable than they appeared, because they could drive away their enemies by inflicting injury at a distance, whilst remaining out of range of hostile or predatory teeth and claws.
The australopithecines could only have survived by becoming expert at throwing stones. A shower of stones can kill any animal which cannot run away (people have been executed by stoning) and well-aimed sharp stones would drive away a leopard or a lion. Against an animal which can run away, the value of stoning is primarily defensive; but in conflict with a predator, defensive action is all that is needed. Predators are careful to avoid injuries because even a minor injury can diminish their chances of killing prey and can rapidly lead to starvation. Stones - or better still, sharpened stones - can be an effective defence, in the right hands, against predators.
The human throwing action is very complex. Great power and accuracy can be achieved by coordinating all the muscles of the arm, wrist, fingers and back - even of the legs. We do not know whether the australopithecines could throw missiles as well as the best of us can. But if, as it seems, the ability to throw missiles effectively was a fundamental factor in bipedal survival, then the evolution of those muscles (and of the brain which controlled them) must have been influenced by the need to develop that ability. We humans are perhaps (among many other things) animals evolutionarily designed to survive by throwing missiles.
So it seems that the long struggle for bipedal survival and ultimately human dominance over all other species began when the australopithecines differentiated themselves as apes which lived mainly on the ground, walking, running and when necessary fighting on their back legs only, using their hands and arms to throw missiles and wield weapons They were the only animal, at that time, which could drive away predators and competitors whilst avoiding combat at close quarters. Our own ancestors, probably close relatives, later succeeded even better.
The australopithecines had brains no bigger than a chimpanzee’s and were certainly not people. They were bipedal apes. They remained very vulnerable at night and like baboons, probably climbed trees or to high places for safety. But like people later but unlike any other animals, they had learned to transcend the limitations of their own bodies. What we people cannot achieve with our own bodily apparatus, we have learned to achieve with the aid of external tools, equipment and weapons. Without wings, we have somehow learned to fly. Without sharp teeth, horns or hooves, first the Australopithecines and later people learned to defend themselves and to keep enemies at a distance with missiles . The stone missiles of those bipedal apes were the first step in the direction of the more sophisticated missiles of the twenty-first century. And the long story of pre-human and human development - a story in which we gradually became complete masters of our environment - began with them.
The Australopithecines were the first successful ground-dwelling apes. They survived, multiplied and diversified for three million years. But like the baboons, they were not fully adapted to life on the ground and probably needed to retreat to trees or high rocks at night. Their arms were longer than ours and they were probably much better climbers than we are. But their brains were still chimp-sized and their upright posture prevented their brains from growing any bigger.
When the australopithecines adopted the upright posture, the pelvis had to change, to allow for the new centre of gravity of the body and for the bone and muscle modifications required for walking vertically on the back legs. But the pelvis is also a girdle through which the infant head must pass at the time of birth. Changes in the shape of the pelvis made it more difficult for the australopithecine infant to pass through his mother’s pelvic girdle. Any bigger brain at the time of birth would have meant too many natal fatalities. The australopithecines failed to solve this problem. Their successful competitor (our own ancestor) did solve it and developed a much bigger brain.
A 900cc brain, which would gradually evolve to around 1400 cc (the average size of our modern human brains) was made possible by specialised adaptation of the female pelvis (with some loss of speed and agility in females) and by giving birth at an earlier stage of foetal development. Births remained difficult (they still are) but at some stage it became usual for "midwives" - older experienced women - to assist the process of birth.
The successors of the Australopithecines still at first had brains considerably smaller than ours. But in most other ways, their skeletons (and presumably their bodies) were very similar to present-day Homo sapiens. We shall call them pre-humans.
The pre-humans were omnivorous and enterprising. Nature offered many foods for them to live on. The greatest problem facing them during most of their long apprenticeship amid nature was not food but defence. Even today, when all animals fear us in daylight, it can be dangerous for us to sleep on the ground in Africa at night But although they were surrounded by dangers of all kinds, the pre-humans became accustomed to living in open country and remaining at ground level even after dark As their numbers grew, they displaced the australopithecines everywhere in Africa and then over hundreds of thousands of years they expanded to the far and often cold limits of Asia and Europe. Their success was owed to new skills and new resources.
It’s well known that the pre-humans made stone tools. But how their “tools” were used is not always clearly understood. This applies in particular to the commonest and most impressive tool of all - what is today known as a “handaxe.” A handaxe was a piece of stone about the size of the human hand, chipped into the shape of an almond kernel. The edge was sharpened all the way round. Handaxes have been found in great numbers all over Africa and Eurasia.
Australopithecines defended themselves primarily by throwing stones. It was logical for the pre-humans, skilled as they were in flint tool making, to modify stones so as to achieve a more effective result. We cannot duplicate the throwing situation or easily assess their skill at throwing. But we know that the handaxe design, once arrived at, was used continuously for more than a million years. We have to assume, without fully understanding how and why, that (either because of aerodynamic qualities or due to its effectiveness as a weapon, or both) the handaxe performed this essential function and performed it well.
A handaxe thrown, with the benefit of training and example based on literally hundreds of thousands of years of practice, must have been a dangerous weapon, capable of causing serious injury. It would not usually kill or even disable the target. To kill a large animal, a small, sharp stone point needs to gain momentum and penetrative power by being hafted on to a wooden shaft. No such hafted spear points or arrowheads appear until about the time that handaxes ceased to be made. But handaxes were not meant to be hunting weapons. They may have been used to kill small animals and they were certainly used on occasion in battles between males for dominance. But they were first and foremost weapons for defence against predators.
Handaxes, following the same basic design, were made over a very long period of time. The design appears not long after stone tools were first invented. The handaxes made more than a million years later - around 500,000 years ago - are better made, but essentially similar and clearly designed for the same purpose.
For no less than a million years of pre-human development, during which brains greatly increased in size, handaxes were completely familiar items in the pre-human toolkit, so that their owners probably would not have been able to visualise life without making them and using them. Then around 50,000 - 100,000 years ago, handaxes ceased to be made and their function was forgotten.
For a very long time, handaxes were the main item in the pre-human armoury, just as canine teeth are the main item in the armoury of a baboon. Baboons use their canine teeth to protect themselves and their young against predators; males also use their teeth to fight against or threaten competitors in struggles for dominance. Threats, of course, are sometimes enough. Confronted by a magnificent display of teeth, a rival may think again. Even a big cat may withdraw and look for easier prey. The owners of handaxes probably also knew how to display them in the same threatening way and this may explain why a few impressively big handaxes have been found which appear too heavy to be efficiently thrown.
Handaxes superseded the simple, unworked stone missiles which were used earlier - used not to kill prey but as defensive weapons against predators, notably big cats. Stunned and perhaps seriously injured in the face, the cat would retire as fast as it could, leaving the human child safe or the recently killed antelope uneaten.
Animal food (often from big animals) appears to have been an increasingly important part of the pre-human diet, and would have been much more valuable when fire was available to cook it. But this does not necessarily imply ability to kill big animals. The pre-humans had no weapon which could do that. But if a well-aimed handaxe could drive a great cat away from a child, it would be equally effective at driving it away from a heavy animal which it had just killed. The pre-humans were more likely to have been prey-stealers than true predators.
Even true predators are also prey-stealers. All predators are always on the lookout for recent kills by their competitors and a victim is not always even initially eaten - and unless easily portable, hardly ever completely eaten - by the animal which made the kill. All members of the dog family are adept at this way of obtaining second-hand meat. But our ancestors were probably better at it than even the dogs are. Compared with wild dogs, people had a great advantage. They could drive the big cat away without exposing themselves to its teeth and claws.
At some time within the last two million years, humans or pre-humans started to make use of fire. Until the publication of Richard Wrangham’s very convincing and readable book Catching Fire , it was thought that fire was tamed much later. It now seems more likely that pre-humans had fire ever since they first started to spend their nights in open country.
The effects of the regular use of fire must have been extremely dramatic. Fire illuminated and scared away predators at night and provided warmth in a cold climate. Above all, cooking revolutionised eating patterns. Uncooked food demands continuous chewing; it uses up more calories to chew and to digest and it may yield fewer calories in the end, because digestion is often only partial, especially of foods like raw meat, to which our digestive system is not well adapted.
Chimpanzees spend most of their waking hours gathering food and eating it as they gather. Other herbivores do the same. Chimpanzees also hunt, kill and eat small animals, but they cannot digest the meat very well because they must eat it raw. Australopithecines probably behaved similarly. By contrast, humans typically cook most of their food and eat it in family groups at the end of the day. That way, we gain more calories and are able to eat a much wider range of foods.
It now seems almost certain that fire had to be tamed before the pre-humans could feel safe in open country at night. Of course it might not always have been possible to light a fire anew every evening, especially in cold and damp conditions, when fire was most needed. The ability to make fire at will, which we take for granted, cannot be assumed even in the more recent prehistoric past.
Settled agricultural communities later kept fire going continuously in a communal hearth (often invested with religious significance, as in the Roman temple of Vesta). Pre-agricultural people nearer our own time often carried a smouldering ember around with them if they expected to need to make a fire. The people Europeans first encountered in Australia carried fire in their canoes. It must often have been difficult to keep fire going; and to let it go out could mean no supper and a very dangerous night. So the need to come back at night to a regularly tended fire must have encouraged a static life in a fixed territory, in a social group big enough to spare a member who could be trusted to reliably tend the fire while others gathered food.
Dogs may also have been used as predator alarms. Pre-humans and dogs were natural competitors. But there were also strong incentives for co-operation. Pre-humans could offer dogs their intelligence and their ability to fight enemies at a distance; dogs could offer pre-humans their highly developed senses of smell and hearing. At some stage, probably much later, the two species learned to hunt together. But the first form of co-operation probably made use of dogs to raise the alarm at night.
Initial co-operation of this kind could have happened quite accidentally. There must have been many conflicts between pre-humans and dogs, fighting for a carcase killed by a large cat. Dogs would sometimes be killed and themselves eaten. Perhaps a puppy might be captured, tethered, fed on scraps and kept for eating on a day when meat was in short supply. At night, it would unconsciously have made itself useful. Its sensitive nose and ears would notice the approach of predators and give the alarm. The lesson once learned, young dogs could be captured and kept for this specific purpose.
Dogs diverged genetically from the wild canine stock around 40,000 years ago, about the time that humans attained decisive control over their environment and still 30,000 years before any other animals were domesticated. From that time on, captured canines would seldom have interbred with wild ones and would gradually have assumed the form of domesticated dogs. But for a very long time before that, during the hundreds of thousands of years when pre-humans still feared nocturnal predators, it may well have become common for tethered wild puppies or comparatively docile bitches to be kept and fed - simply to act as predator alarms at night. Guard dogs (or alarm dogs) may have been part of pre-human life for as long as fire. Interbreeding with the surrounding wild dogs made sure that their skeletal remains are indistinguishable from them.
During the million and more years of pre-human development, our ancestors were only one animal species among many and by no means the most powerful, numerous or important. 60,000 years ago - only two or three thousand human generations - our picture of the past shows us a world which was still dominated by very large animals. In particular, mammoths and other members of the elephant family were to be found in large numbers almost everywhere in the world. Elephants feared few predators and had adapted to almost every kind of climate. Their overwhelming influence on the environment - still true of a few small areas of Africa - was probably once the rule almost everywhere.
Besides elephants, the pre-human environment included many other huge and powerful animals, now extinct. They had tough hides. How effective would stone missiles, clubs and wooden spears have been against a herd of mammoths, some of them bigger than an African elephant? Until about 50,000 years ago (less than 2000 generations ago in Europe) people always lived in fear of large animals and had little control over the environment in which they lived. Agriculture was inconceivable because crops would have been trampled and eaten. Permanent dwellings (unless in caves or other inaccessible locations) would always have been liable to be overrun.
Living in this dangerous environment, over a period of several million years, which ended only about a hundred thousand years ago (later in Europe and Asia), first the australopithecines and then the pre-humans survived and created a favourable ecological niche for themselves, probably above all because they could defend themselves and their young by the use of natural and artificial weapons - particularly missiles - which enabled them to keep their enemies at a safe distance. When they learned to cook their food, the same skills enabled them to steal the meat of big animals by driving predators away from their kills. Like chimpanzees, they could make tools and weapons out of perishable materials; unlike chimpanzees, they also learned to shape stones and this greatly extended their armoury and toolkit. They were highly intelligent and they were probably the only primates to successfully colonise colder climates. At some stage they learned to use fire. But their environment was dominated by animals much larger and more powerful than themselves; they lived in the shadow of the megafauna.
By around 100,000 years ago, there were three species or perhaps sub-species of pre-humans, separate and identifiable now by small anatomical differences. In Europe and Central Asia lived the Neanderthals, heavily built, chinless and with big brow-ridges. In Africa lived pre-humans who were (judging by skeletal remains) by this time anatomically more or less identical to ourselves. In Asia lived the descendants of earlier pre-human migrations from Africa.
Despite anatomical differences, all these varieties of pre-human seem to have shared, (to judge by the artefacts which have survived and allowing for differences in locally available materials) essentially the same culture and way of life. The artefacts found in South Africa differ little from those found in Europe. Like their ancestors a million years earlier, they lived as animals among other animals. There had been comparaively few changes over that million years. Despite their modern bodies and full-sized brains, their lives seem to have been totally different from the lives of any people living now or in the known historical past.
When Europeans first explored the world in our own time, they encountered an immense variety of different cultures, customs and languages. An explorer travelling the world 100,000 years previously would have been able to find “people” almost everywhere in reasonable numbers, but he would have been struck by a drab uniformity of culture everywhere. Just as a particular animal species looks and behaves in much the same way from one end of the world to the other, so the pre-humans would have seemed to him much the same from South Africa to China.
What kind of creatures were they? Were these pre-humans people like ourselves? Can we imagine people so conservative that their technology and probably their way of life remained almost unchanged for a million years? Yet in contrast to the australopithecines, the pre-humans had skeletons and even (in later pre-humans) brain capacity (1300-1400 cc) little different from our own. Nevertheless we must avoid anthropomorphism: skeletal resemblance is not enough. In particular, we should not necessarily assume that the pre-humans had what we call language. Highly intelligent animals as they were, they could undoubtedly communicate with one another. But did they speak a language or languages? There are some good reasons for suggesting that they did not.
Discussion of whether or not they had language normally takes place in terms of physical anatomy. But it is important also to consider the social implications of language.
Animals communicate with one another in surprisingly complex ways. In the words of Dmitri Bayanov, “By the communication means at their disposal, animals can greet, warn, threaten, frighten, order, tease, invite, entice, deceive, ask for, beg, give consent and show indifference, surprise, bewilderment, respect, contempt, contentment. A bee through her dances can indicate to her sisters the direction and distance to nectar-laden flowers, which the instructed bees don’t fail to find.” Nevertheless all known forms of animal communication are much less complex than human languages.
Human languages rely on arbitrarily chosen vocal symbols. These symbols differ from one human language to another. There is no special reason why “child” should be conveyed by “child” in English, but by “enfant” in French; but so it is. The concept is much the same but the word is different.
A human language is a kind of code. It functions on the basis of words - unique verbal symbols which correspond to all the objects or ideas which the speakers of that language need to communicate to one another. It also has rules, followed habitually by its speakers, for linking the words of the language together.
Languages in the sense in which we understand them have developed as the common means of communication of large groups of people who habitually communicate with one another and communicate less often with outsiders. A language draws together the people who speak it, and excludes others. The rules for using a language are followed by all members of the linguistic community, for all wish to be understood. Those rules are typically paralleled by other rules - or laws, conventions, customs - which all also have to follow if they wish to be socially accepted in that particular social and political community. To be able to speak a language is a badge of membership of a community. It ensures acceptance by other members, provided the other rules of the group are also followed.
Language networks minds together. The possession of a common spoken language (and even more, the later possession of a common written language) enables each member of a community to benefit from the communicated experience of others, so that the mental capacity of each separate individual becomes less important. It enables fellow-members of a society to share information and experience.
Communities speaking a single language are typically endogamous breeding populations. Matings outside the language group do happen, but they are occasional exceptions, rather than the general rule. Thus an individual typically grows up speaking a particular language and all his or her life is spent amongst others who also speak that language. Those who speak other languages may be regarded as outsiders, even enemies. The endogamous continuity of each group is maintained by difficulties of communication and differences of social custom (and often overt hostility) between one group and another, so that “peoples” become partially separated gene pools, drift apart a little genetically and start to seem different from one another even in their appearance.
Animal social groups (among animals which are social at all) are much less distinct and separate from one another. They may be temporary accumulations, like flocks of birds. If they are more permanent, they are often simply large families, male-centred (deer, walruses) or female-centred (bees, elephants). Larger groups are typically bands, seldom containing more than a hundred individuals, all of whom know one another (chimps and many monkeys). These bands re-form over time as individuals leave them to form relationships with individuals outside the group or as quarrels or limited territorial resources cause groups to split up. They are not big enough to be long-term breeding populations; to avoid in-breeding, either males or females (it varies from species to species) typically leave the band after puberty and find mates in other groups; so that neighbouring groups, although they are generally hostile to each other, are constantly exchanging members. The whole species, even if it covers a wide geographical area, forms a single integrated gene pool.
Before 100-50,000 years ago, we probably have to imagine a widespread human species - or perhaps sometimes a number of different human species - divided into a very large number of families or small groups but with groups and families constantly dissolving and new ones being formed by immigration. Our species probably consisted of a single very large gene pool; as with all other animals, there were territorial barriers but no sharp genetic or cultural barriers at any point between neighbours.
There is a complete contrast between this probable uniformity within a species and the incredible diversity which we find in the languages and customs of even the earliest groups of true humans that we know about - those hunter-gatherer peoples who survived long enough to be described by recent explorers and anthropologists. The aboriginal people of Australia, numbering perhaps a million, spoke about 300 different languages . Each language group had its own customs; each was a partially separated gene pool. The populations of pre-European North America (now USA and Canada) were similarly fragmented. This fragmentation - linguistic, political and genetic - is typical of all humans and sharply differentiates us from all other animals.
It seems that the distinguishing characteristic of humanity - which makes us different from all other animals and probably explains our dominance over all other forms of life - is not our bipedalism, or even our brain size, but our possession of language and our co-operative social organisation. The advent around 50,000 years ago of what has been called “the Palaeolithic Revolution” was a turning point in the process of change from a genetically unified species of animals to the linguistic, political and genetic fragmentation which is typical of Homo sapiens.
In this short account, I’ve tried to show how, by fairly logical stages, a group of apes learned how to live successfully on the ground and gradually acquired the bodies, including the brain capacity, of people living today. This had happened by around 100,000 years ago. The “pre-humans” whom I have described, were, by 100,000 years ago living in bodies like our own. But their way of life was very different from ours. It was that of an unusual and very successful species of animal. Extrapolating what had happened in the past, they could perhaps have continued the slow pace of their development for hundreds of thousands, perhaps millions more years. But that did not happen. Around 40-50,000 years ago, our picture of the past totally changes. We suddenly find ourselves in a world we can recognise. The great archaeologist Richard Klein summarises the evidence of change:
Previous chapters have emphasised that before 40 thousand years ago - that is, before the Upper Palaeolothic and comparable cultural manifestations had completely supplanted earlier ones - vast areas were characterised by remarkably uniform artifact assemblages that differed from one another mainly in the relative abundance of the same artifact types. In addition, artifactual change through time was painfully slow: basic assemblage types lasted tens or even hundreds of thousands of years. ....After 40 thousand years ago, however, the general pattern changed radically. Like-aged artifact assemblages from neighbouring regions often differed qualitatively and within single regions the pace of artifactual change accelerated dramatically.
(R G Klein, The Human Career)
Klein shows us that until around 40,000 years ago, pre-human culture was uniform over wide areas and changed very slowly. But about that time, newcomers spread over Africa and then into Eurasia. These newcomers (from whom we are ourselves descended) continually developed new weapons and tools; and the weapons and tools they made differed from one area to another. All kinds of innovations appeared. Tools and weapons began to be produced made of ivory, bone and shell. Good quality stone materials were carried from one place to another. For the first time, traces of permanent buildings appear. People produced art. They fished. They made boats. They spread rapidly across Eurasia and by about 40,000 years ago, they had crossed the sea and settled in Australia.
These people had skeletons and presumably bodies similar to those of the people (we have been calling them pre-humans) that they displaced. There is some evidence of genetic mixing But they were not pre-humans - their way of life shows that they were unquestionably human in the full sense.
Klein has given an excellent Youtube presentation on the subject. The only explanation Klein has given for the sudden change is the idea of a sudden genetic mutation. Klein is not a geneticist and David Reich, who is, casts polite doubt on Klein's explanation. Others have questioned the suddenness of the revolution. But no one who contrasts the million years of pre-human development before it with the accelerating speed of human development since, can doubt the importance of the change. It started in Africa and subsequently spread throughout the world. How it happened and why, we don't know.
The first and one of the most significant formal human burial sites in the world, dated at around 30,000 years ago, is at Sunghir, about 250 km east of Moscow. 10,000 years earlier, the area had been on the fringes of that occupied by the Neanderthal pre-humans. The people who dug the graves were very different. The site seems to have been the centre of a summer hunting ground. It contains the graves of two adults and two children. Their garments have decayed, but they were ornamented with more than 13,000 beads made of mammoth ivory. The beads must have been produced by a large number of people over a considerable time. The buried children, so richly clothed, must either have had a high inherited social status or (perhaps more likely) must have been sacrificed as part of an important communal rite. Either way, they show that we are looking at a human society much more like those of historical time - a group including many individuals who were not all closely related to each other, yet who participated in common rituals and felt they belonged to a single community.
The larger social unit must have made possible a developed division of labour. It also made possible the rapid development of innovations within individual endogamous tribal groups; innovations which would not necessarily spread to other tribes immediately, because of cultural and language barriers and inter-group hostility. The wider communities - or tribes - in which people now lived must each have been bound together by a common language and have formed a partially separated gene pool. This is enough to explain the cultural diversity which Klein describes; and the absence of this cultural diversity before fifty thousand years ago suggests that in the earlier period, no such languiage barriers existed.
Let's return to the subject of language. We do not know for certain that the people who emerged from Africa and rapidly replaced the pre-humans all over their territory 50,000 years ago spoke, from the beginning, languages like our own, whereas their hominid predecessors did not. But there are two reasons for suggesting that this was so. Firstly, there must have been some reason why these people were able to progress so much faster than their predecessors; and secondly, the archaeological record shows not only that progress became much faster, but that there was much more cultural diversity, with significant differences in artifacts between one area and another. These differences suggest local cultures which are likely to have corresponded to different communities speaking different languages.
It may be that the distinguishing characteristic of humanity - which makes us different from all other animals and may help to explain our dominance over all other forms of life - is not our bipedalism, or even our brain size, but our possession of language and our large scale co-operative social organisation. This appears to have date from some time before 50,000 years ago as part of a change - from a unified species of animals to the linguistic, political and genetic fragmentation which is typical of Homo sapiens.
To sum up: the people who became widespread 50,000 years ago appear to have possessed two very great competitive advantages over (as far as we know) all previous forms of animal life. They spoke languages; and they probably lived in organised political and economic communities, each separated from the next by linguistic, political and cultural barriers and forming a cooperative entity and a partially separated gene pool. The larger economic communities meant greater division of labour, more specialised skills and the emergence of many new techniques and weapons. With these new techniques and weapons, the political communities of mankind quite quickly achieved complete domination over their environment.
It was suggested earlier that during the long period of pre-human life on the ground, the greatest problem facing our ancestors was not food but defence against predators. Times had now changed. From around 50,000 years ago (only about two thousand generations before our own) human populations expanded rapidly and filled more and more of the world. The growing tribes, equipped with new weapons and employing large-scale co-operative hunting and defensive methods, were now able increasingly to hunt and kill any animal, however big, and keep their children safe from any predator, however clever and powerful. Food now became the priority. Life was straightforward for as long as the tribe was able to control enough territorial resources to feed its population. Each tribe, held together by common cultural, linguistic and political bonds, typically occupied and defended a territory against neighbouring tribes. As populations grew, the need for more food led to attempts at territorial expansion and hence to inter-tribal warfare.
There seems no reason to doubt that people have always been territorial and no doubt the pre-humans, like other primates, were territorial before them. Where there is territoriality, there will be disputes. Disputes between individuals or families seldom lead to actual bloodshed. But when serious disputes arise between large communities occupying adjacent territories, bloodshed has historically been the rule rather than the exception. This has been so from the beginning:
The facts recovered by ethnographers and archaeologists indicate unequivocally that primitive and prehistoric warfare was just as terrible and effective as the historic and civilised version. War is hell whether it is fought with wooden spears or napalm. Peaceful prestate societies were very rare; warfare between them was very frequent, and most adult men in such groups saw combat repeatedly in a lifetime. As we have seen, the very deadly ambushes, raids and surprise attacks on settlements were the forms of combat preferred by tribal warriors to the less deadly, but much more complicated battles so important in civilised warfare. In fact, primitive warfare was much more deadly than that conducted between civilised states because of the greater frequency of combat and the more merciless way it was conducted.
(Keeley War before Civilization p174)
As individual tribes increased in numbers, territories expanded in the direction of least resistance. Tribes occupying coastal territories vigorously resisted encroachment from inland neighbours, having nowhere else to go; the inland neighbours therefore moved further inland, until the habitable parts of Africa and Eurasia which could provide a good supply of food were progressively filled. Finally, some tribes in coastal territories which had developed fishing and had made boats, under pressure from inland, ventured further out to sea in search of new lands to occupy.
People reached Australia around 40,000 years ago. At that time, western Indonesia was joined to Asia and New Guinea was joined to Australia. There was still a significant sea crossing, including one island-hop of over 50 miles, but they survived it, and colonised an isolated world occupied by a wide variety of large marsupials. Many of the marsupials were considerably bigger than those still living in Australia today; but by comparison with the elephants and other giant mammals of Africa and Eurasia, they were much smaller and less intelligent and must have been far more vulnerable to human hunting.
The effect of human arrival in Australia was dramatic. All the giant marsupials disappeared not long after the arrival of human hunters. It seems likely that Australia was the first major continental area in which humans became the dominant species and were able to take control over their environment. If Australia had contained food plants suitable for cultivation and animals suitable for domestication, it might have become the birthplace of agriculture and perhaps of civilization.
Since people now had boats, many other extinctions probably also took place on large and small islands during the same period. In the continental Old World, the megafauna was far more formidable. Changes were at first less dramatic. The destruction of large animals took longer. But by 15,000 years ago, organised humans, now increasingly equipped with hafted spears and later with new weapons like the spear-thrower and the bow, had caused widespread extinctions everywhere. Elephants and mammoths, rhinos and woolly rhinos, wild horses, giant deer, hippos, musk oxes and the sabretooths which had preyed on them suddenly (in a few thousand years) disappeared from Europe.
The most dramatic effects were felt in America, colonised quite recently (probably less than 15,000 years ago) when weapons and hunting techniques were even more highly developed. Glaciation reduced sea levels and for a time, a land bridge existed between Siberia and Alaska. Animals came across from Siberia and colonised first the bridge and then America. Human tribes came over at about the same time: perhaps following the game, perhaps fishing further and further along the coast in their boats. Perhaps they even crossed the narrow northern Pacific a little earlier.
The newly discovered American continents were uncolonised and unhunted. They were inhabited by an immense range of animals, including many members of the elephant family, camels, wild horses, giant beavers and ground sloths. These animals were preyed upon by predators including sabertooths, scimitartooths and cheetahs. Human predation was unknown to them. Within a few thousand years of the arrival of humans, two things had happened. The human population of America had expanded to fill both continents, down to the tip of South America. And all these big animals and many more had become extinct.
Hunting has always been, for men, a sport as well as (sometimes) a source of food. We don’t know how the hunters reacted to their new situation of power and plenty. Did they conserve the game, once they had all the food they needed? Or like a modern landowner shooting his pheasants - or like a fox in the henhouse - did they slaughter far more than they needed, for the sheer joy of it? In the case of the elephants, there was another reason why slaughter may have exceeded what was needed for food. Ivory had already (as we have seen at Sunghir) become a useful and valued material.
But the great age of hunting could not last. After America had been colonised, there was little further scope for human territorial expansion. Animal numbers declined dramatically. The more vulnerable prey animals, once extinct, were no longer available for food. Everywhere, human populations grew rapidly until the game became harder and harder to find. Everywhere there was famine, because of a sudden collision between expanding populations and declining resources of food. As growing tribes of hunters followed diminishing supplies of game, tribes fought one another for territory and hunting rights. Accustomed to a meat diet which was now often unobtainable, spending more and more of their energy in fighting other human competition rather than hunting game, people sometimes took to cannibalism.
Populations too big for the resources of their territory searched for every possible new kind of food. People living on the coast devised new means of catching fish in quantity. In northwest Europe, excavation has suggested that communities existed for whom the hazelnut harvest was a major source of food. Even in recent historical times, the people of Corsica lived very largely on chestnuts. But nuts never became a long-term solution to the imbalance between population and food supply. No satisfactory solution emerged until cereal cultivation became the norm. And with elephants and other large animals now less of a problem, settled cultivation was now possible.
The transition to agriculture has always been hard to explain. Why should people have given up an enjoyable lifestyle and a varied diet and adopted lifestyles and diets which were often very tedious and limited? In the words of Mark Nathan Cohen “the adoption of agriculture probably resulted in an increased per-capita work load and a decline in the quality of the diet”.
Pre-agricultural peoples had a varied diet and their food-gathering activities must often have been satisfying for their own sake. The “hunter-gatherers” were after all using their mental and physical resources for the purposes for which they were intended by nature. Their lives were sometimes short, but they were probably happy. By contrast agriculture, particularly before the employment of draft animals, involved a great deal of mechanical backbreaking toil. Food preparation was hard work also, given that cereals had to be ground by hand. And the final result, for most people, was a monotonous staple diet and not much else. Why did people adopt agriculture?
The answer seems to be very simple: expanding human populations meant that they had no choice. Cohen’s book explains the only possible reason why humanity embarked on the agricultural revolution: agriculture yields more calories per hectare; it was the only way that the available land could be made to yield sufficient food to feed its human population:
The development of agriculture was an adjustment which human populations were forced to make in response to their own increasing numbers. By approximately 11,000 or 12,000 years ago, hunters and gatherers, living on a limited range of preferred foods, had by natural population increase and territorial expansion fully occupied those portions of the globe which would support their lifestyle with reasonable ease... After that time, with territorial expansion becoming increasingly difficult and unattractive as a means of adjusting to growing population, they were forced to eat more and more unpalatable foods. In the period between 9000 and 2000 BC. populations throughout the world, already using nearly the full range of available palatable foods, were forced to adjust to further increases in population by artificially increasing, not those resources which they preferred to eat, but those which responded well to human attention and could be made to produce the greatest number of edible calories per unit of land. (Cohen, The Food Crisis in Prehistory)
Cohen successfully presents the case that agriculture was a natural extension of techniques already in use to increase the yield of natural resources. It was not ignorance, but lack of need, that previously prevented people from practising cultivation. Agriculture did not make for an easy life and did not immediately result in more acceptable food; its only advantage was that it produced more food per unit of land and so enabled the same area to support more people.
Human populations worldwide formed a territorial network covering the entire habitable landmass of the world; further population could no longer be accommodated by wider human dispersion. There was famine throughout the landmass, and where local conditions permitted it, more intensive land-use was the only possible answer. That is why agricultural societies appeared at about the same time in several widely scattered locations.
Ways were to be found to make unpalatable foods more acceptable. But dense agricultural populations living on limited diets became more liable to disease. Repetitive strain injuries must have become the normal lot of people engaged in constant mechanical work. And not everybody adjusted equally well to the work ethic. History shows that those who adjusted less well sometimes adopted what seemed to them like a more attractive alternative - to live on the toil of others. Denied the pleasure of hunting animals for a living, many men and many tribes of men turned their weapons against other men and attempted, with varying success, to obtain by robbery, conquest and enslavement what they were unwilling to work for.
Making use of their pooled resources of intelligence and experience, people had expanded to the limits of the world. They now totally dominated their environment. Many people’s lives were difficult But some were able to develop specialised skills and achieve independence and fulfilment as priests, scribes, craftsmen and traders, making themselves useful to their neighbours rather than enslaving them. In spite of everything, agriculture was the way forward: it meant a much more assured food surplus and permanent human settlements; it led everywhere, quite rapidly, to cities, literacy and civilization.
This short account has followed the changing relationship with their environment, first of the pre-human bipeds and later of the humans who displaced and succeeded them.
The story started in Africa with the Australopithecines: apes probably in many ways very much like their ape relatives, but who had sacrificed some of their tree-climbing ability, in return for being able to walk and run efficiently on the ground on their back legs only. Their hands were thus set free to throw missiles, wield clubs and of course carry around their young, their weapons, ammunition, food supplies and whatever else was useful to them.
They were intelligent, adaptable and omnivorous but relatively slow and vulnerable; so they probably had less of a problem with food-gathering than with defence. Their young depended on them for protection for many years. Their environment was tropical Africa, full of deadly predators of all shapes and sizes, virtually all of which could run faster than they could and many of which were highly intelligent and very agile climbers: not only the great cats, smaller cats, jackals and hyenas, but snakes, eagles and their own relatives the chimpanzees, all of which, if not prevented, would kill and eat their young. Even in the trees, life had not always been easy; as they increasingly spent more time on the ground, it is hard to understand how they survived at all. But they did.
We think we know how they managed it: unlike every other animal, they defended themselves and their young not with inbuilt weapons - teeth, claws, hooves or horns - but with natural or artificially adapted temporary extensions to their arms - missiles and clubs. They could fight enemies effectively whilst themselves staying out of range of the enemy’s weapons.
These animals lived and diversified for more than two million years; as long a period as has elapsed since they disappeared. They were displaced by animals we call pre-humans - bipeds who were more completely adapted to life on the ground; who could probably climb less well but who made up for it by greater intelligence and perhaps greater skill with their hands. These newcomers - our own closest relatives - could probably throw more effectively and they developed the ability to shape weapons and tools not only from soft materials but from stone, yielding sharp points and edges. They learned how to use fire.
The pre-humans became, over time, better adapted to life outside the tropics. They expanded their territory to include southern Eurasia. Increasingly, their skill with sharp missiles made them feared and avoided by small birds and mammals. They could drive predators away from their young with a barrage of missiles and they probably used the same technique to obtain meat by driving predators off their kills. They looked increasingly like people. But the lives they lived were very different from those of any humans, because they lacked language. They lived in small, exogamous groups, their environment shaped and controlled by the megafauna, above all by the mammoths.
And so life continued and little changed - for literally hundreds of thousands of years.
And then suddenly, quite recently, only about fifty thousand years ago, everything changed. From somewhere in Africa emerged true humans - people who appear to have differed individually little from the pre-humans, but who had language and social organisation. They could communicate detailed information and instructions to one another and organise themselves not in tens but in hundreds or even in thousands. What ten or twenty pre-humans could not achieve together, an army of hundreds of humans could. An army of hundreds, wisely led, was more than equal even to the largest herd of mammoths. New weapons and sophisticated hunting techniques suddenly made the greatest and most powerful mammals vulnerable as never before. The empire of the elephants was challenged. The great tusks of the mammoths became a human raw material.
Within perhaps ten thousand years - only five hundred generations - the newcomers spread from their African origins all over the Eurasian territory of the older pre-humans, and further north. Even the sea was no longer a barrier to them. They fish in it, and voyage in search of new lands to conquer. At the farthest limit of Eurasia, they rowed or sailede beyond the horizon, over fifty miles of sea and discovered Australia - a new continent, a hunter’s paradise, where even the biggest animals were vulnerable and even the most intelligent apparently unaware of danger. Glutting themselves on meat and losing scarcely any of their children to predation, the newcomers rapidly increased in numbers and spread throughout the new land - until their increasing collective appetite encountered a decreasing supply of food. In a continent not well endowed with edible plants, they people through a painful period of famine, and finally settled into a new rhythm, exploiting their mastery of their environment to maximise its yield by the use of fire.
In Eurasia and Africa, the same process was at work, more slowly but still very rapidly in terms of geological time, and with accelerating speed. The mammoths and many other prey animals also in the end proved too vulnerable and were hunted to extinction. As in Australia, so in Eurasia and Africa, people ran very short of food.But here, they found a better answer. They learn to greatly increase the food yield of their environment by turning it into farmland. They took control also of herds of herbivores, defend them against predators and other human hunters and organised them to produce meat, milk, wool and hides in a sustainable way. Much the same thing happened later in America.
All this occurred in perhaps forty thousand years - probably less than one per cent of the time which has elapsed since the appearance of the australopithecines; yet already, under human control, the whole aspect of many parts of the world completely changed. And change accelerated. Human communication became possible, not only throughout communities of living people, but over time and over great distances, by means of writing. Tribes of hundreds or thousands gave way to empires of millions, ruled from cities of tens and even hundreds of thousands. Human mastery of the environment started to include not just the living world but the elemental forces of nature. Despite wars and conflicts, human trade and co-operation became more and more world-encompassing. Most recently the world has been linked everywhere by a complete system of electronic communication.
And still, only about fifty thousand years has elapsed since the first real people emerged from Africa. Only about two thousand generations have lived and died since the dramatic arrival of mankind. If there is such a thing as a miracle, mankind is one.
To understand the impact of the Origin of Species, we must see the world as it appeared to the early nineteenth century.
The astronomical discoveries which we associate with Copernicus, Galileo and Newton had revolutionised European man's perception of his position in space. It had become clear to all educated people that that the earth was not the centre of creation, but a small planet circling one among many stars, situated at immense distances from each other in a virtually limitless universe.
But the change in perception of space had brought no corresponding change in the perception of time. The universe was still assumed to have been created at a fixed date, certainly not more than 10,000 years ago. All the species of animals and plants now in existence were explicitly believed (in England at least) to have been created in their final form at the time of the Creation. The dates that were suggested for the beginning of the world (on the basis of the Book of Genesis) correspond approximately to what we now know to be the dates of the first settled civilizations in Egypt and Mesopotamia.
Historical evidence was absent before that date. But increasingly, scientific observers were becoming aware of the existence of fossils. Fossilised bones - of unknown and presumably extinct animals, some of them of colossal size - had been discovered. Fossils of what appeared to be sea-creatures had been found in rocks high on mountains. For the collectors and scientific observers of the eighteenth century, fossils (though increasingly studied) were an enigma. Only vast and incalculable forces - whether of flood or of earthquake and eruption - could, it seemed, account for such momentous changes as the rise of mountains from the bed of the sea. When had these appalling events occurred, why had we no other record of them, and why had the fossils been deposited in layers, with different types or species commonly found in specific strata?
The eighteenth-century geologist James Hutton belonged to the sceptical Scottish circle of Hume and Adam Smith. Hutton was the first to suggest the principle that the past development of the earth must be explained only by the same kind of changes that are still in progress today. ‘No powers' he wrote ‘are to be employed that are not natural to the globe, no action to be admitted except those of which we know the principle'. He studied the effects of sedimentation and volcanic activity and explained the events of the past on the same slow-acting principles. This led him to demand an immense time-scale. 'In the economy of the world' he wrote 'I can discover no trace of a beginning, no prospect of an end.'
The theories of Hutton were regarded as atheistical, but had little impact, partly because they were obscurely presented. But by the early nineteenth century, canal-building and the development of coal-mining in Brtain led to an increasing study of the structure of the earth. The professional surveyor William Smith (later to become known as "the Father of English geology"produced the first geological map of England and Wales. He showed thatspecific types of strata could often best be identified by the fossils which they containedand that these fossil forms succeed each other in a specific and predictable vertical order that can be identified over wide distances. Nevertheless the full implications in terms of time scale were not established.
By this time biological research among living species had been increasingly professionalised, developing most strongly in France. Cuvier's classification of the species of the natural world was not far from what became established later. The structure of the living world clearly divided into related groups of species: genera, families and orders of animals. Cuvier suggested that old forms had become extinct as a result of successive floods and new forms had each time taken their places. The possibility that similar species and groups had simply developed over time was explicitly suggested by Darwin's grandfather Erasmus Darwin and by Cuvier's French rival Lamarck. The theory of evolution - or something like it - already existed. But it had not yet acquired any accepted scientific basis and was usually known as transmutation or transmutationism.
Then in his Principles of Geology (1830-33), Darwin's contemporary Charles Lyell revived Hutton's principle of slow geological change, and presented a classic explanation of development over millions of years. Among scientists at least, his account soon came to be widely accepted. Darwin took Lyell's book with him on his trip to South America on the Beagle.
Despite his perception of geological time, Lyell at first explicitly dissociated himself from the theory of the "transmutation" of life. But his theory of long-term, gradual geological change inevitably made the theory of common descent seem much more likely. If species had appeared and become extinct at different times over an immense period of time, surely God had not continually intervened with new batches of creation?
But if life had developed in a gradual way, why had it done so? The challenge was to present some convincing scientific hypothesis which would explain the development of life - and the ability of nature to produce new species each so marvellously adapted to its environment. There was a very strong psychological pressure to come up with the missing piece in the jigsaw - a theory which might explain how and why new species have developed to fit new environmental conditions.
At the same time, there were attempts to trace the emergence of higher species over time on the analogy of the development of embryos. The Industrial Revolution and increasing European world dominance were producing a sense of confidence in the future, which was reflected in theories of progressive historical development. "Transmutation" was in the air. But though the theory was attractive, it was also dangerous; it inevitably encountered the active hostility of most churchmen, yet it could not count on the support of the scientists because they could not find any plausible explanation for it and were nervous of antagonising the Church without feeling much more sure of their ground.
Nevertheless the extent to which the public would respond to the idea, when it came, was revealed by the immense success (a succès de scandale) of the Vestiges of the Natural History of Creation , published in 1844. This book, the anonymous work of a successful Scottish publisher, Robert Chambers, presented a broad popular view of science and the universe, in which Lyell's time-scale of geological development was combined with ideas of evolutionary change, up to and including man.
Chambers' book was exciting and imaginative but it contained many scientific inaccuracies and it provided no explanation for transmutation which would stand up in scientific terms; it was furiously condemned by both church and science, in chorus. This made no difference to its popularity: Chambers brought out successive new editions in which he adapted his theory to the criticisms that were expressed of it.
So before the Origin of Species was published, evolution (as "transmutation") was a familiar idea to the intelligent reading public. It made sense if one looked at the fossils in the rocks. But the scientists had not been able to find a convincing explanation for it. However much he tidied up his details in the light of current scientific knowledge, Vestiges could never command the respect of the scientific community, because it offered no credible reason why evolution had taken place. The Anglican Church taught explicitly that the marvellous complexity of the living world was the best possible proof of the existence and omnipotence of a divine designer. No evolutionary theory could be scientifically respectable, or could effectively challenge this doctrine, until a hypothesis could be found - it need only be a hypothesis - which could provide a possible scientific explanation for the complexity and diversity of nature and explain how living things, unaided by divine design, had become so perfectly adapted to their ways of life.
Darwin had spent five years on an extended voyage as ship's naturalist on HMS Beagle , studying in particular the the animals, plants and geology of South America. What he had seen influenced him greatly:
During the voyage of the Beagle I had been deeply impressed by discovering in the Pampean formation great fossil animals covered with armour like that on existing armadillos; secondly by the manner in which closely allied animals replace one another in proceeding southwards over the Continent; and thirdly, by the South American character of most of the productions of the Galapagos archpelago, and more especially by the manner in which they differ on each island of the group; none of the islands appearing to be very ancient in a geological sense.
He felt increasingly that only a theory of the progressive development of life could explain the fossil evidence, yet he could find no reason for it to have occurred:
It was evident that such facts as these, as well as many others, could only be explained on the supposition that species gradually became modified; and the subject haunted me. But it was equally evident that neither the action of surrounding conditions, nor the will of the organisms (especially in the case of plants) could account for the innumerable cases in which organisms of every kinds are beautifully adapted to their habits of life..
He felt he could not publish his acceptance of transmutation unless he could explain it:
I had always been struck by such adaptations, and until these could be explained it seemed to me almost useless to endeavour to prove by direct evidence that species have been modified..
He set to work, following the example of Lyell in geology, to collect material which seemed relevant to a theory of the development of life over time.
Then he read Malthus. The influence of Malthus was crucial for Darwin (as also later for Wallace). Malthus has acquired a bad name because his theoretical conclusions led him to suggest that charity to the poor often does more harm than good. As a practical political thinker, his influence may have been harmful. But his theoretical conclusions led naturally to the theory of natural selection. Malthus pointed out that
..through the animal and vegetable kingdoms nature has scattered the seeds of life abroad with the most profuse and liberal hand. She has been comparatively sparing in the room and the nourishment necessary to rear them. The germs of existence contained in this spot of earth, with ample food, and ample room to expand in, would fill millions of worlds in a few thousand years. Necessity, that imperious and all-pervading law of nature, restrains them within the prescribed bounds.
When Darwin read Malthus he realised that he had found the basis for his theory.
In October 1838, that is, fifteen months after I had begun my systematic enquiry, I happened to read for amusement 'Malthus on Population' and being well prepared to appreciate the struggle for existence which everywhere goes on from long-continued observation of animals and plants, it at once struck me that under these circumstances favourable variations would tend to be preserved, and unfavourable ones to be destroyed. The result of this would be the formation of a new species. Here then I had at last got a theory by which to work..
Darwin came to the conclusion that there was an analogy between the influence of the human breeder and horticulturist and the action of "natural selection." The breeder selects desirable traits in domesticated animals and breeds from them, to create new varieties often quite remote from the original strain. In the same way, traits in wild animals which helped them to survive under wild conditions would enable them become the parents of the next generation. In the following generation, the same thing would happen again. The process would be cumulative over thousands of years, and the end result would be a new species better adapted to its environment than its ancestors.
A very large part of Darwin's work, subsequently summarised in his Variation of Animals and Plants under Domestication, related to artificial rather than natural selection. He studied in detail and relative to many species the art by which the breeder or the horticulturist is able to produce new varieties by selection, choosing as parents for the next generation only those individuals which show a small variation in the desired direction; the effect of their selection thus builds up cumulatively in successive generations, resulting in major changes.
I collected facts on a wholesale scale, more especially with respect to domesticated productions, by printed enquiries, by conversation with skilful breeders and gardeners, and by extensive reading..
He wrote two short summaries of his theory and in 1856 was advised by Lyell to "write out my views pretty fully" and he at once began to do so, in great detail. It seems likely that a very large part of this work would actually have dealt with variation under domestication. But he was interrupted by the arrival of a letter from Alfred Russell Wallace, enclosing his paper On The Tendency of Varieties to Depart Indefinitely from the Original Type. Wallace's paper outlined (entirely independently of Darwin but influenced like Darwin by Malthus) the principle of natural selection.
There were at that time almost no professional scientists in Britain; science (apart from medicine) was scarcely taught at British universities. The scientific discoveries of the preceding century and a half had been made, in general, by amateurs - enthusiastic gentlemen who, like Darwin, had private incomes and (particularly in biology) by beneficed clergymen with time on their hands in country parishes. There were many collectors - of beetles, butterfies, stuffed birds and mammals and of course fossils. Much of their collecting they did themselves. But they were also served by paid collectors and by professional dealers. The aristocrats among the paid collectors were a few enterprising young men who at the risk of thir lives, travelled to the tropics where they could, if they were lucky, obtain and bring or send back exotic and valuable specimins.
Alfred Russel Wallace (see link) was one of these. After working at different times as a surveyor/builder and a teacher and after reading the Vestiges, Wallace together with his friend H W Bates had decided on an expedition to the Amazon, with the dual object of making their fortunes and establishing a more firm scientific basis for the transmutation theory. Wallace returned three years later on a ship which caught fire in mid-Atlantic and he lost his specimins and notes. Undeterred, he made a second expedition to the islands of what is now Indonesia. By this time he had become one of Darwin's many collectors and had published a nunber of articles in scientific journals. His paper On the Law which has regulated the Introduction of New Species (1855) had been recommended to Darwin by Lyell and another correspondent and had already caused him some apprehension that he might be forestalled (see link p537).
Wallace's second paper was a bombshell:
Darwin was stunned. "I never saw a more striking coincidence," he moaned helplessly. "If Wallace had my MS sketch written out in 1842 he could not have made a better short abstract"....He was well and truly forestalled. All his originality was smashed, all his years of hard work suddenly useless. For a moment the news hit him like the death of a child.
Janet Browne Darwin: the Power of Place p15
After some heart-searching, Darwin consulted his friends Lyell and Hooker. Perhaps fortunately, it was impracticable to discuss the situation with Wallace, who would not be able to reply to a letter for many months. It was decided to submit Wallace's paper, along with some notes of Darwin's own on the same subject to a meeting of the Linnean Socity, for subsequent publication. Then Darwin immediately set to work. The Origin of Species, a summary of his work over the previous twenty years, was published the year after. It caused an immediate sensation.
Darwin had arrived at the hypothesis of natural selection long before he received Wallace's paper, and his slowness in publishing his conclusions must be explained by an awareness of the dramatic effect likely to be produced by a serious presentation of "transmutation" implying a scientific endorsement of man's animal descent. As a former disciple of Paley, Darwin must also have known that (in England at least) the faith of many if not most sincere Christians was based to a large degree on "natural religion." Natural religion - covered in more detail in the next section of this site - was the belief that animals and plants had been designed by God and were living proof of God's existence, wisdom and goodness. Darwin had himself shared this belief. Natural selection, he now realized, might appear to make this belief unnecessary, because it could provide an alternative and perhaps more truly scientific explanation for the perfect adaptations of nature.
It could also be said that Darwin had a superb sense of timing. Because in fact the blow he inflicted came with much more force than it would have done twenty years' earlier. Vestiges had prepared the ground and biblical criticism was increasingly casting doubt on the literal truth of the Bible.
Darwin knew that it was vital that he should have a hypothesis which would provide a new and rational explanation of the reason why living things have evolved as they have; but he was reluctant to rely upon the natural selection theory too heavily, and his presentation of a supplementary theory of ‘sexual selection', which he was to develop later, shows that he was aware of one of the most obvious objections to it.
His omission of the connection to man was tactical. He knew that the implication would be understood by most readers, but he also knew that an explicit statement of man's origins would immediately increase the anticipated level of opposition:
It would have been useless and injurious to the success of the book to have paraded, without giving any evidence, my conviction with respect to (man's) origin.
The 1860's was a decade of intense controversy. Darwin initially plugged his book by sending free copies and requests for comment to his wide circle of friends and colleagues. After that he took less part, his principal champion being T H Huxley.
Huxley read the Origin just before publication and was immediately convinced. He immediately went to work and contrived to review the book anonymously, at length and very favourably in the Times.
This was an extraordinary coup. The Times - then at the height of its power - was at that time the almost universal morning newspaper of the British educated class. The Times, in that period, made and unmade governments. Throughout the world, the newspaper was regarded as the authoritative voice of Britain; at a time when Britain was the richest, most powerful and most scientifically advanced country in the world. A terrible blow was struck at the Christian Church; and by a remarkable irony, Huxley's review appeared at Christmas - in the Times issue of December 26th 1859. No new idea has ever been launched with more thorough preparation, or with greater immediate impact, than Darwin's theory of evolution.
Huxley's Times review was a clever piece of journalism which helps us to place Darwin's book in the historical context of transmutationism:
.. the transmutation theory, as it has been called, has been a "skeleton in the closet" to many an honest zoologist and botanist who had a soul above the mere naming of dried plants and skins. Surely, has one such thought, nature is a mighty and consistent whole, and the providential order established in the world of life must, if only we could see it rightly, be consistent with that dominant over the multiform shapes of brute matter.
The Times Dec 26th 1859
Whilst paying lip-service to the "providential order" Huxley presents the case that biology, like other sciences, cannot simply depend on supernatural explanations for what we see in nature. Just as the other sciences had found physical causes for observed phenomena, so we must not be frightened to look for them in biology:
What is the history of astronomy, of all the branches of physics, of chemistry, of medicine, but a narration of the steps by which the human mind has been compelled, often sorely against its will, to recognise the operation of secondary causes in events where ignorance beheld only an immediate intervention of higher power?
The Times Dec 26th 1859
For Huxley, evolution was his opportunity. He was a younger man, established as a scientist, but with his public reputation still to be made. He wrote to Darwin:
‘I trust you will not allow yourself to be in any way disgusted or annoyed by the considerable abuse and misrepresentation which, unless I greatly mistake, is in store for you. You must remember that some of your friends, at any rate, are endowed with an amount of combativeness which (though you have often and justly rebuked it) may stand you in good stead.
I am sharpening my claws and beak in readiness.' ( see link )
Throughout the 1860's, evolution was a subject of intense controversy. Alvar Ellegard compares the reaction towards Chambers' Vestiges of Creation, in 1844, with that towards Darwin's Origin of Species, fifteen years later. In many ways, the reaction of press and public to the two books was similar. But if the Vestiges was more widely read, the Origin was taken more seriously:
In a sense, the Vestiges acted more strongly on the popular mind than the Origin. The book was quite as much talked about in the press in the first few years, and had undoubtedly a much wider readership. It appealed to the imagination by treating Evolution as concerning the whole of nature, and not just the organic world. Yet in spite of this, "Vestigianism" never reached the proportions of Darwinism as a matter of public concern. The Vestiges was a popular success, but no more. No scientific authority ever came forward to support its thesis. The Origin was sometimes taken as a more learned and less comprehensive imitation of the Vestiges - it was in fact described as such by the Daily News reviewer in 1859 - yet since it was perforce taken seriously by the intellectual elite of the country, the questions which it raised, whether great or small, soon took on a much deeper significance than had ever been granted to the speculations of the Vestiges. The broad public perhaps did not realize precisely in what way Darwin was more significant than Chambers, but the stir he caused in the intellectual world showed that he was. Darwinism concerned, as one popular commentator put it, 'the tremendous isues of life."
Alvar Ellegard : Darwin and the General Reader, p333.
By the end of the 1860's, the battle, as far as Britain was concerned, was largely won. Most of the younger scientists had accepted evolution at once; the older scientists mostly came over gradually, or were themselves discredited; the educated public and most of the press, already prepared by Chambers' Vestiges, came over also: some but not all churchmen fought on, but did themselves no good by it. The controversy increasingly resolved itself into a battle between the traditional authority of the Church and the new and growing prestige and professionalism of the scientists; and the scientists won.
Nevertheless Darwin's victory was at that stage an incomplete one. Darwin had persuaded most people that "transmutation" was an acceptable scientific explanation of the geological past, but he had not necessarily persuaded them that natural selection was the cause of it:
It is clear that Darwin's contemporaries were, in a way, prepared for an evolution theory. But they were not at all prepared for the sort of evolution theory which Darwin actually propounded. This contradiction explains one of the paradoxes of the subsequent development of opinion: though it is practically certain that the evolution theory would not have been established at all if Darwin had not been able to support it by means of the naturalistic theory of Natural Selection, yet the majority of the general public, and a good many scientists, refused to accept the Natural Selection theory, while allowing themselves to be converted to evolutionism.
From this point of view Darwin may be compared with Columbus. In believing that the world could in principle be circumnavigated, Columbus was in no way original. But he produced a major change in our perception of the world as a result of his mistaken confidence in the ease of circumnavigating it. In rather the same way, Darwin's belief in evolution was not new. But the route he found to it - his theory of natural selection - made it accessible to science as a serious hypothesis.
U nderstanding of the origins of new species has been revolutionised by the work of Ernst Mayr (particularly his book Population, Species and Evolution ) But it has taken time for thr full implications of his work to be understood and presented in simple language. At the risk of over-simplification, the account below attempts to clarify the issues and explores some of their implicatiions.
Modern biology teaches that animals divide into about ten phyla, of which the phylum of chordates includes the vertebrates and some others. The next main subdivision is that of class, followed by orders, families and genera. Finally we reach the individual species, which may be divided into sub-species.
The higher-level classifications of classes, orders and so on are of great importance to the biologist but for most of us they are of little practical significance. But the species distinction is vital to us. It doesn’t matter much to us whether we are primates or insectivores. It does matter profoundly to us that we are people and not chimpanzees.
Whereas the other classifications belong to the world of science, the species distinction is a fact of nature. Our own strong feeling that we are people rather than any other animals, leads us to behave quite differently in relation to any member of our own species from the way we behave in relation to other animals.
We are not alone in this. All animals behave quite differently in relation to other members of their own species. In particular, they treat all members of the same species, but of the opposite sex, as potential mates. Mating within the species is encouraged and outside the species is effectively prevented by behavioural, visual, auditory and chemical (smell) signals which attract a potential mate but serve as isolating mechanisms, deterring members of other species, however closely related, from attempting to mate. In our own case it may be significant that the human male, whilst strongly attracted in many ways to the receptive females of his own species, finds the visual signal given by our nearest relative - the swollen sexual organs of the receptive female chimpanzee - particularly uninviting.
A species represents a breeding and genetic unity with isolating mechanisms which separate it from other species. The need to mate binds all members of a particular species together into a breeding population which shares a common gene pool. The basic characteristics of the species are determined by a genetic structure which, despite limited individual variations, is common to all members of the pool.
Within the limits of the common genetic structure of the species, small changes can occur easily - for example, external pigmentation often adapts to the environment. Some members of a species may adopt white protective coloration in winter in places which have a great deal of snow. In warmer climates, other members of the same species may be the same colour at all times of the year. Size and other external characteristics can also change.
Domestic dogs provide an extreme example of the variations in colour, size and shape which can occur (though among wild species, they seldom if ever occur to the same degree) within a single clearly defined species. But despite all their variations, all dogs recognise all other dogs immediately as dogs and behave quite differently towards them from the way they behave towards all other animals. Although each breed of dogs represents a partially (artificially) separated gene pool, they are not yet very far apart genetically. All share a fundamental canine identity which comes from the basic genetic structure common to all members of the species.
So that despite this external flexibility, the basic genetic structure of the species changes much less easily. For as long as they still belong to the same breeding population, there appear to be strict limits in the extent to which individuals are able to vary from the common characteristics and structure of the species.
Nevertheless the conservative pull of the large gene pool no longer operates if the pool is divided into two or more units by physical barriers. Gene pools divided by physical barriers tend to develop in different directions.
The speed with which differentiation occurs once the breeding population (the gene pool) is divided, is affected by differing ecological conditions, so that the animals on the two sides of the barrier are subject to different competitive pressures. Climates may be different, feeding habits may change as a result of different foods becoming available; competition from other species may change behaviour, predation may be more or less important and may take different forms.
When a barrier separates the gene pools of the two branches of an existing species, they will (particularly if conditions are different on the two sides of the barrier) gradually become differentiated. If differentiation has gone far enough, the removal of the geographical barrier will not reunite the species; the animals coming from one side will be unable to mate successfully with those from the other. One species will have become two.
The development of many different species over millions of years appears in fact to have been stimulated by the geological and climatic changes of the earth. Animal populations have been divided and reunited at various times as the continents have moved, as new land has been created by volcanic action and as land and sea levels have risen and fallen. The divisions and reunions have enabled new species to come into existence and to radiate over their potential territory.
The effects of geographic barriers which break up the gene pool can be studied in populations which have become cut off from their origins, frequently on islands. This is often found with land-dwelling birds which do not normally cross the sea but may occasionally be blown off course. Thus they may accidentally populate an archipelago (like the Galapagos) off the coast of a continent.
A small flock of continental birds arriving accidentally on an island - particularly if they arrived there before people had boats - would have found themselves in a new environment in which there were both problems and opportunities not present in their original home. Many islands contained no mammals except those which had been able to fly or swim there (e.g. bats and seals). So it would have been less dangerous for a bird to spend time on the ground. Far more fledgelings would perhaps initially have survived. But equally, the bird's most frequent food might not be easily available. Rapid population expansion in the absence of the usual predators might typically have soon led to an urgent need to adapt to other kinds of food.
Perhaps only twenty or so birds would have formed the new island population; perhaps fewer, the minimum number being a single fertilised hen. Thus the gene pool would have been small. Small gene pools are much less stable than big ones - they often produce eccentric variants. These eccentric variants are usually counter-productive, resulting in the extinction of the eccentric line. But eccentricity sometimes works. In the great majority of cases, the immigrant birds would have failed to adapt and soon have died out. But in a few cases, the new population would have survived and adapted. Thus the beginnings of a new species would have come into existence. Separated from the parent species of the mainland, it would have started to develop new isolating mechanisms. These would steadily have reduced the forces of mutual attraction between the island colonists and the original population. Any members of the island sub-species which accidentally found their way back to the continent would nevertheless initially have been re-absorbed into the parent species. But as the new sub-species gradually developed further and further away from their original form, a point would be reached when cross-mating with mainland birds would no longer occur. At that point a new species would exist.
The new species on its island would probably have become less specialised than before, able to eat a wide variety of foods which happened to be available there - perhaps animal food as well as plant food. Let us now suppose that a few of these birds drifted to another island in the archipelago and founded a new population on it. Whilst similar in many respects, the new island offered a slightly different range of food, with perhaps less plant food but more animal food. The new population, whilst still eating plant food also when available, would have become slightly better adapted to eating animal food.
Having passed through the long process of separate speciation, a few of the second island's birds may have found their way back to the first island. Two populations would have been in competition there, one relatively a little better adapted to animal food and the other to plant food. Over time, each would have become progressively more specialised in the food source where there was least competition, and the original stock would have given birth to two new species, a seed-eater and an insect-eater.
Why do we think that this is what happens? The formation of new species (like the formation of rocks) is a slow process and cannot be observed and recorded from start to finish in nature. But the separate stages of development have each been separately observed. Islands close to continents typically contain local variants of those continental bird species which had been able to cross in small numbers, occasionally, from the mainland. Sometimes these island variants have reached the stage of being separate species, sometimes not. And the process of archipelago bird colonisation which I have described is more or less what is believed to have occurred on the Galapagos (see link ). Varieties of finch, obviously closely related but separate species, have diversified through the Galapagos archipelago to occupy ecological niches typical elsewhere not of finches but of warblers, woodpeckers and others. The phenomenon of the Galapagos birds influenced Darwin in the thinking that led to The Origin of Species .
Islands are probably the commonest environment in which a small population of animals has been isolated and subjected to conditions demanding new adaptations. Islands have produced a very large number of unique and unusual species. On islands, adaptation to changing conditions is compulsory, if the species is to survive. On the continents, it is optional; there is often an easier option - migration. When the glaciations came and went, continental species well adapted to particular temperatures and vegetation patterns moved north and south with them. But a species isolated on an island which was becoming warmer or colder would have had to adapt to the new conditions or perish. Conversely (as Darwin pointed out) climatic change on an island can open up a range of new ecological niches to be filled by animals that can adapt to them. On the continents, these niches would be filled immediately by inward migrants.
So for a number of reasons, islands have always been full of unusual animals. To give a single example: each of the major islands of the Mediterranean, islands off the coasts of California and Siberia and islands not too far from continents in other parts of the world all once possessed their own species or variety of dwarf elephant (see link ). All must have evolved from animals which had occasionally swum across from the mainlands (elephants can swim long distances) or (perhaps more likely) been left behind when sea levels rose.
Most of the varied and unusual species living on islands - including the dwarf elephants - have now disappeared. Since people began to visit and colonise islands in boats, hunting and bringing domestic animals and small rodents, very widespread extinctions have occurred. But if we go back to the period before people became able to cross the sea, we have to imagine a world in which every island had its own specialised animal life.
Until people arrived in boats, the only opportunities which island species had of colonising the continents arose from changes in sea levels or underlying geology which destroyed their geographical isolation. These changes did not happen very often. When an isolated island species became exposed to continental competition in this way, the result was probably most often the rapid extinction of the island species. But not always. Occasionally, an eccentric island variant turned out to have developed characteristics which enabled it to compete successfully elsewhere.
Island origin answers a number of questions. It goes some distance towards explaining why paleontology has so far seldom found the direct ancestors of modern forms. This would not be surprising if many new species - including perhaps our own - had first started to differentiate themselves in a micro-population on an island. The micro-population might be too small to leave much trace, and the island might now be under the sea.
Of course not all new species appear on islands. Island location is only one possible form of geographic isolation. For fish, rivers and lakes perform a similar function. The crucial point is that new species typically appear, initially, as isolated small populations. In most cases, the reintegration of the isolated population into a larger environment results in its extinction. But new species, when they do appear, spring from the small minority which survive and spread successfully in the larger environment. In the words of Ernst Mayr:
"The widespread occurrence of geographic speciation is not now seriously questioned by anyone....Most isolates are ephemeral; they become extinct before they have had the opportunity to function as full species.. Peripheral isolates are produced 50 or 100 or 500 times as often as new species, but when a new species evolves, it almost invariably evolves from a peripheral isolate."
Successful new species normally arise not from the gradual large-scale transformation of successful existing species but from small-scale origins, from which they emerge to challenge the dominance of existing forms of life, sometimes expanding very rapidly when the existing species fail to compete successfully with them; and thus giving the impression of very abrupt change when we look at the fossil record. Abrupt change of this kind does not result from a sudden genetic mutation in the continuing population, but from an incoming species displacing the previous species from its ecological niche; in the way that the immigrant grey squirrel has recently and within less than a hundred years displaced the indigenous red squirrel ( see link ) in the U.K.
Life has evolved over very long periods of time, during which mountains and sea levels have risen and fallen many times, islands have separated from continents and been reconnected; and living populations have been ceaselessly divided up by natural barriers and later brought together again, perhaps in different combinations. Geological and climatic change and the occasional dramatic meteorite arrival have served as the engines of evolution. Changes in the land and freshwater environments have over and over again exposed isolated populations to the challenge of revolutionary adaptation to new conditions. Most have failed to adapt. Those who succeeded sometimes (very occasionally) later conquered the bigger areas. Taking advantage of the new wealth of opportunities now available to them, they have increased in numbers, variety and perhaps in physical size.
By contrast the oceans, the greatest and most stable environment in the world, containing innumerable different forms of life but with very few natural barriers, have for a long time now produced relatively little which is new. The most important events in the evolution of the sea in the last two hundred million years have all come from the land: first the very successful marine reptiles; then the marine mammals and birds who displaced them; most recently the fisheries and pollution brought by man. The land and its rivers and lakes are where innovative evolution has been happening. This has implications for any theory of evolution by natural selection; for natural selection operates in the sea as elsewhere
Natural selection is the system which enables the forms of life to adapt to changes in their environment. It is a self-regulating system. Alfred Russel Wallace, the co-discoverer of natural selection who precipitated the writing of the Origin of Species, took as an analogy one of the first self-regulating systems devised by man - the centrifugal governor which Watt fitted to his steam engine:
The action of this principle is exactly like that of the centrifugal governor of the steam engine, which checks and corrects any irregularities almost before they become evident; and in like manner no unbalanced deficiency in the animal kingdom can ever reach any conspicuous magnitude, because it would make itself felt at the very first step, by rendering existence difficult and extinction almost sure soon to follow.
Wallace 1858: On the Tendency of Varieties to Depart indefinitely from the Original Type
Just as the thermostatic system of the human body regulates the blood temperature to a constant level, despite wide variations in external temperatures, so natural selection adjusts a species to keep it in the best possible harmony with the environment in which it is currently living. Animals typically produce far more young than can conceivably survive and each generation produces many variations. Only those best adapted to current conditions live to reproduce and to pass on to their offspring the variations which have enabled them to survive.
Thus a gradually changing environment can induce progressive adaptation to the new conditions which it imposes. Natural selection ensures the survival of the fittest - those most fit to survive and flourish in a particular environment at a particular time. But it is increasingly realised that natural selection is blind. It cannot predict the perhaps dramatic changes of the future. Greater fitness at a particular time, in a particular environment, frequently means specialisation - and therefore less fitness for other environments. Evolutionary lines which specialise too much are often dead ends. In the words of the evolutionist Theodosius Dobzhansky:
It may seem strange that evolution controlled by natural selection so often leads to overspecialization and consequent extinction. But this is only a consequence of the fact repeatedly emphasised above that natural selection is opportunistic and like any natural process other than the human mind, lacks foresight. Selection perpetuates what is advantageous here and now, and fails to perpetuate what may be beneficial in the future unless it is immediately useful.
Dobzhansky: Evolution, Genetics and Man P369.
Successful populations, like those of the ocean, are steady, unchanging populations. In genetic terms, they remain constant, with little genetic drift. Natural selection may enable them to gradually get just that little bit better at doing what they do, but they do not modify their limbs for new purposes, or start to breath through lungs instead of gills. They just carry on as they always so successfully have done, until something happens which breaks all the previous rules: and this typically results in their extinction. They are then replaced by new populations which are the progeny of previously less successful animals, but which have somehow acquired a new and decisive advantage over them.
In the short term, survival is best ensured by maximum adaptation to the environment in which an animal finds itself. This is the business of natural selection. But in the long term, the animal lines which prosper are those which (whilst adapting enough to ensure survival) retain sufficient flexibility to adapt to totally changed conditions when this becomes necessary. And of course this adaptability may make future success possible but cannot guarantee it - it all depends on how the circumstances and opportunities of the future pan out.
A simple example is the forelimb. In most mammals, this has been adapted for efficient quadrupedal locomotion, with some allowance often also made for weaponry (claws or hooves) and perhaps digging. Most four-footed mammals became less good at gripping branches and holding objects. But primates retained the original five digits. Despite the general evolutionary advantages of paws and hooves, they retained their digital flexibility.
It happened subsequently that primates became highly intelligent and that a particular group of primates became bipedal. The combination of high intelligence with forelimbs able to manipulate objects proved to offer completely new opportunities which nobody could have predicted.
Natural selection provides an excellent answer to the question "Why are life-forms so well adapted to their environment?" - the question which the pre-Darwinian naturalists could only answer by the argument of divine design. But to be confident that natural selection is enough to explain evolution requires faith rather than just rational deduction. Science requires more evidence.
There has never really been any question of evidence or proof. Darwinian materialism is based, like Christianity, or like Marxism, on belief. It is an answer to the nineteenth century question "If I cannot any longer believe in the book of Genesis, what can I believe in?" For those of us who grew up in the twentieth century and have never dreamed of believing in the book of Genesis, or any other simple religious package, this is an unnecessary question.
Evolution is the study of the pre-human past. Like the study of the human past which we call history, it is a fascinating story, with much to teach us. But perhaps we should approach it with open minds, in the spirit of historians rather than theologians.
Historians first try to find out what happened. Then they seek to explain how and why particular events happened. They do so not in terms of abstract theory or dogmatic belief but by studying the people, background and circumstances of the period leading up to the events in which they are interested. Only a few historians have claimed that the past can be explained in terms of a consistent long-term theoretical pattern. Marx did: he claimed to have done for history what he thought Darwin had done for evolution. For a considerable time, many people in large areas of the world believed that Marx had indeed done so. Very few people still retain that belief.
Evolution is extraordinary and cannot be easily explained. Our first feeling is one of wonder. How could it possibly have happened that, even over hundreds of millions of years, primitive and relatively simple animals - to leave out other types of life - could have evolved to produce the extraordinary wild fauna of a hundred thousand years ago? And who could have predicted that in only a short stretch of geological time, almost all the great mammals of that period would have disappeared, in a world totally dominated on land and sea by - of all things - a primate!
And is it not even more extraordinary that this primate has developed ways of researching the past and (within limits) understanding what has happened? Let us not stretch probability even further by claiming that the primate has also discovered exactly why it happened.
Professor Thomas Alerstam ends his fascinating book Bird Migration with these words:
We are compelled to resign ourselves to continuing uncertainty and confusion over how birds find the right migration route...
So, this book ends with an unsolved mystery. Actually I do not think that this is any major shortcoming. It might be hoped that we humans would gain a greater degree of inspiration from unsolved mysteries than from what we believe we know - in great things as in small. May the birds continue to fly over the earth, and may mankind wonder and investigate.
Perhaps there will always be "unsolved mysteries" and the true scientist, like a good historian, recognises them and does not pretend to an understanding which he does not have.