Darwin's Island Page 5
The loss of our native nudity was an early hint of the evolutionary talent that made us unique - the ability to respond to a challenge not with bodies but with brains. Clothing allowed us to spread across the world, for with its help we take the tropics with us wherever we go.
Adam and Eve, in their sultry paradise, were unashamed, but after the first (and least original) of all sins they made aprons to hide their nether parts. When did they first put them on? Lice hint at when garments were invented. Chimps and gorillas have lots and spend many hours grooming as a result. When humans emerged on to the sunny savannahs they lost their hair. The lice had a hard time and evolved to live in the few patches of habitat left. We now have three kinds, the head and the body louse, plus the pubic louse. The body louse is the only one that hangs on to clothing. The pubic version is closest to the lice found on gorillas and may have joined us from there. DNA shows that the other two evolved from a chimpanzee parasite which began its intimate acquaintance with our own bodies six million years ago. The body and head forms, in contrast, separated more recently - perhaps no more than fifty thousand years before the present. That may mark the moment when we first donned our vestments and gave a resourceful louse a new place to live. Men, their parasites prove, dressed themselves as they took their first steps towards the icy north.
Since then we have learned to cope with external parasites with insecticides, with cold with central heating and with noxious foods with kitchens. Each talent is a product of the contents of the skull, which are - like Adam’s underpants - unique. Darwin noted that ‘There can be no doubt that the difference between the mind of the lowest man and that of the highest animal is immense’, and he was right. To understand human evolution we need to know how and why our brain, the most human of organs, is so different from that of any other primate and why and how our behaviour is even more so.
The structure is three times as big, and the cortex, the thoughtful bit, five times larger than that of the chimpanzee and the modern skull is several times roomier than that of three million years ago. Chimps are born with a brain almost as big as that of an adult animal while babies, whose brains are already larger than that of a chimpanzee, continue to invest in grey matter until they are two. Genes active within the human cranium have multiplied themselves when compared with those in other primates and one such, which when it goes wrong leads to the birth of infants with tiny heads, has evolved particularly fast. The nerves within the human skull are more connected to each other, and their junctions more sophisticated, than are those of the chimp and the structure is also busier at the molecular level. Even so, much of the DNA most active in that part of the body has changed no more rapidly than that at work in liver, muscle or scrotum.
The brain is expensive, for by weight it uses about sixteen times more energy than does muscle. That represents a quarter of the entire budget of the body at rest and means that we expend twice as much effort on the intellect as do chimpanzees. How can we afford such a luxurious appendage? Humans eat no more than other primates of comparable size but have a richer diet, with more meat and fewer roots and leaves, than do our relatives. As a result we need smaller intestines to soak it up. We also invest less in muscle than other apes and the enzymes that burn food are more efficient than theirs. All this began, like black skin, a million and more years ago, when people moved from forests to savannahs, travelled in larger groups and became better hunters with a meatier diet. The way to man’s brain was through his guts.
Even so, today’s organ of thought is no bigger than that of the Neanderthals. Fossils of their newborns show that they were born with a brain as large as our own, which grew even faster during infancy, but those creatures acted far more like apes than we do. Something more than an extra dose of grey matter has made us what we are. To quote Darwin: ‘of all the differences between man and the lower animals, the moral sense or conscience is by far the most important’. A glance at our relatives shows how right he was.
Chimpanzees are nastier than many people like to think. They kill monkeys and are pretty unpleasant to each other too. Their sex lives would shock Queen Victoria and their ethical universe, if they have such a thing, is far darker than our own. They live in groups, but the groups break and reform as their members quarrel. Terror makes the world go round. Set up a task in which two chimps need to pull a rope to get a tray of food. They will, but only if they are out of reach of each other. Otherwise, the dominant animal attacks its subordinate even if neither then gets anything. Anger and greed destroy the hope of reward. What makes humans different is a loss of fear, odd as that sounds in a world where that emotion seems to be everywhere. When anxiety goes, society can emerge.
Our social skills begin early. A group of two-year-olds asked to find a piece of food after they saw it moved to a new place or turned to a new position or put in a box with a beep were pretty good at each job - but no better than adult chimpanzees, for both babies and chimps succeeded at about two trials out of three. When it came to the need to learn from others the babies won hands down. They became far better at each problem when they saw someone else solve it, or when an adult pointed to or gazed at where the food was hidden or made noises that told them they were getting warm. Each response demands an insight into another’s inner sentiments. We have a lot more of that talent than do our relatives. The chimps took no notice of those who tried to help.
Chimpanzees can learn, but do not teach: like all apes, they ape but do not educate. In some places, adults fish for insects with a stick or bash nuts with a stone, and the young emulate them. Even so, the grown-ups make no effort to show the infants how to do the job, do not change their ways when youngsters are around and never check to see how well they are doing. Birds, with their bird brains, can do what a chimp does, for a budgie will pull out the stopper of a bottle of food if it sees another do the job, and crows are even smarter.
Real education asks for more. A good pedagogue can teach almost any subject as long as he keeps a few pages ahead of his charges and they respond to his efforts. Teachers also have insight into the mental lives of their pupils, into who understands the lesson and who does not, and know how to encourage them without their becoming bored.
The chimp’s negligence about the next generation is a reminder that the minds of our hairy relatives are not much like our own. A competent teacher needs to understand what his students are thinking - and chimps do not: they have no more than a rudimentary ‘theory of mind’, as psychologists put it. We have lots, and it helps those on both sides of the lectern. Teenagers might doubt the fact, but no ape could ever become a schoolmaster.
The best way of reading a mind is to chat to it. Thomas Love Peacock invented a character called Sir Oran Haut-Ton, who learns to play the French horn but not to speak (he is elected to Parliament, where his silence gives him an air of wisdom). Homo sapiens is the eloquent ape. Even deaf children left in groups babble with their hands. Speech is the scaffold upon which society is built. No other primate can speak and all attempts to persuade them to do so have failed (Noam Chomsky, the theoretician of language, noted that it was ‘about as likely that an ape will prove to have a language ability as there is an island somewhere with flightless birds waiting for humans to teach them to fly’).
The origin of language is a cause of endless dispute which, given that just one creature can speak, may never be resolved. Darwin thought that perhaps it began with imitation: that ‘some unusually wise ape-like animal should have thought of imitating the growl of a beast of prey, so as to indicate to his fellow monkeys the nature of the expected danger’. The Descent of Man also suggests that it could have started with love songs, and that speech was in part a side-effect of sexual selection. Perhaps it was; or perhaps it grew instead from the simple fact that we are social animals. Apes groom each other because the constant pacification calms them all down and cuts down the conflict that is never far from the surface. Big groups demand too much scratching time but reassuring sounds can placate lo
ts of individuals at once. The savage breast might first have been charmed in that way; possibly, indeed, with song - which could be why some stutterers can sing a sentence when they cannot say it.
However it began, language makes us what we are. The ability to speak is coded for on the left side of the brain and plenty of primates have a brain almost as lopsided as our own. Even so, chimp tongues fill their mouths while ours are dainty in comparison. The human tongue has retreated down the throat. The language of Shakespeare is a complex set of sounds made as the space above the larynx flexes and bends. The anatomical changes leave evidence in the shape of the skull. Neanderthals had chimp-like mouths and could do little more than grunt. The first skull capable of speech emerged no more than fifty thousand years ago - not long before the explosion of technology that led to the modern world.
One British child in twenty has some form of speech disorder. A certain rare inborn abnormality makes it impossible for those who inherit it to cope with grammar. Baby mice with the same damaged gene make fewer squeaks than usual when removed from their mothers, and people with a version impaired in a different way are at risk of schizophrenia; of, like Saint Joan, hearing voices that are not there. The normal version found in humans differs in two of its amino acids from that in all other primates. It is foolish to speak of a gene for language but if the transition from animal to human turned on speech it may have involved rather few molecular changes. The situation is confused by the discovery that Neanderthals have the human version of the gene, which must hence date back to our inarticulate joint ancestor.
Wherever they came from, words are the raw material of a new kind of genetics, in which information passes through mouths and ears as well as through eggs and sperm. It moved us on from our status as a rare East African ape to the most abundant of all mammals. Ideas, not genes, make us what we are. Our DNA is not very different from those of our kin, but what we do - or say - with it has formed our fate.
Even so, the famous ‘indelible stamp’ is without doubt imprinted into the human frame. Modern biology shows that chimpanzees are even more like us than Charles Darwin imagined - but in no more than the most literal way. The strengths and the limitations of his ideas in deciphering what makes us human have become ever clearer as knowledge advances. His theory is powerful indeed but enthusiasts need to be reminded where its power comes to an end.
In 1926, the Soviet government sent an expedition to Africa. It was directed by Ilya Ivanovich Ivanov, famous for his work on the hybridisation of horses and zebras by artificial insemination. The Politburo hoped to do the same with men and apes, for the experiment would be ‘a decisive blow to religious teachings, and may be aptly used in our propaganda and in our struggle for the liberation of working people from the power of the Church’. In Guinea, Ivanov obtained sperm from an anonymous African and inseminated three chimps - but none became pregnant. He then planned to fertilise women with chimpanzee sperm, but was not allowed to do so. Back in Russia he set out to do the same with a male orang-utan and a woman who had written that ‘With my private life in ruins, I don’t see any sense in my further existence … But when I think that I could do a service for science, I feel enough courage to contact you. I beg you, don’t refuse me … I ask you to accept me for the experiment.’ The orang, alas, died before its moment of glory and Ivanov was arrested and exiled to Kazakhstan, where he, too, met a childless end.
Americans anxious to stop research in human genetics once attempted to patent the idea of a human-chimp hybrid in order to whip up protest. The application was denied on the equivocal grounds that the US constitution does not allow the ownership of human beings (whether the cross-breed would have that status was not discussed). Artificial fertilisation of chimpanzee egg with a man’s sperm may now be feasible (although claims to have produced a ‘humanzee’ are fraudulent) but is universally seen as beyond the pale. The problem is not one of biology, but of what it means to be human. A hybrid between a chimp and Homo sapiens makes too ready an equation between our apish bodies and our immortal minds.
Charles Darwin was well aware of the limits of his own theory. As he points out in the famous last sentence of The Descent of Man, men and women possess noble qualities, sympathy for the debased, benevolence to the humblest and an intellect which penetrates the solar system. All that does not change the fact that in our bodily frames, most of all when reduced to chemical fragments, we bear the indestructible mark of our humble ancestry.
Some people despise his science as a result, because it appears to destroy man’s special place in nature, but they fail to understand what evolution is all about. Biology, in its proof of our kinship with chimpanzees, underlines its irrelevance to ourselves. The double helix does not diminish Homo sapiens but sets him apart on a mental and moral peak of his own. The theory of evolution does not render us less human than we were before. Instead the insight it provides into man’s place in nature has made us far more so than we ever realised. A century and a half after Queen Victoria’s disagreeable visit to Jenny the orang-utan, I gave a talk at London Zoo which pointed this out - and most of the apes agreed.
CHAPTER II
THE GREEN TYRANNOSAURS
Soaring above southern Venezuela is a hidden landscape: the sandstone plateau of Mount Roraima, an inaccessible peak that is most of the time shrouded in mist. Arthur Conan Doyle used the place, or one very like it, as the location for his 1912 book The Lost World, a tale set in a land of evolutionary imagination, a place of dinosaurs, ape-men and primitive humans, ready to be explored by the irascible Professor Challenger. It was a fearsome spot but the bearded Englishman lambasted the lizards and saved the savages, as any Edwardian reader would expect.
Conan Doyle was born in the year of The Origin. By his fifty-third birthday, the theory of evolution had become so widely accepted that a literary hack could use it as the centrepiece of a work of fiction. Conan Doyle, who had read the reports of the British explorer who discovered the unique island in the sky, seized the chance and his book sold hundreds of thousands of copies to a well-primed public.
In reality the dinosaurs had gone from Roraima millions of years before and the local ‘savages’ never made it to the top. Even so, its remote summit is a genuine lost world, not of giant anthropophagous lizards or man-eating apes but of unobtrusive plants with the same dietary habits. Those green carnivores turn for food not to human flesh, but to insects. They must do so or starve.
Their habit is widespread. Almost six hundred insect-eating species, from all over the world, and from a wide variety of groups, have now been discovered. Their way of life has evolved on many occasions, and the tactics used to trap and digest prey are varied indeed. Separate lineages, from quite different places in the evolutionary tree, have taken up an identical diet and have come to the same solutions to find, digest and absorb their food. Charles Darwin had used such convergent evolution, as the process is known, as evidence for natural selection in The Origin of Species. The similarity of certain Australian marsupials to true mammals elsewhere in the world, or of wings in birds and bats, was, he saw, powerful proof of its action. Unrelated creatures faced with the same challenges adopt structures and habits that look similar but have different roots. As he pointed out, life can reach the same end through quite different pathways: ‘in nearly the same way as two men have sometimes independently hit on the very same invention, so natural selection, working for the good of each being and taking advantage of analogous variations, has sometimes modified in very nearly the same manner two parts in two organic beings, which owe but little of their structure in common to inheritance from the same ancestor’.
Now we know many such examples - flight not just in birds and bats but in squids, fish, dinosaurs, flying squirrels and the marsupial sugar-glider of Australia (not to speak of the flying snake whose flattened body allows it to glide for many metres from a tall tree). We ourselves are not immune to convergence, for plenty of creatures have lost their hair, grown their brains, or even
- as in the meerkats of Africa, who instruct their infants how to eat poisonous insects - stood upright and gained some simulacrum of the ability to educate.
Evolution in response to a common challenge has been so effective that certain creatures once assumed to be close relatives because they are so much alike in form are in fact not real kin: the vultures of the Old and New World, similar as they appear, do not have a recent common ancestor, for the former are eagles and the latter storks. Anteaters and aardvarks, lions and tigers, moles and mole-rats - all hide a bastard ancestry beneath their shared appearance. The process goes further. On Roraima itself, for unknown reasons, melanism is rife among unrelated organisms, and the rocks harbour black lizards, black frogs and black butterflies. The mutation responsible for black melanin pigment is the same, or almost so, in zebrafish, people, mice, bears, geese and Arctic skuas (and perhaps even in lizards and frogs), and has been picked up by natural selection in each. Within the cell, too, shared evolutionary pressures have produced enzymes with distinct histories that have settled on an almost identical DNA sequence in the active parts of the molecule. On a more intimate scale, the complicated chemical used as a sexual scent by certain species of butterfly also does the same job for elephants (which is riskier for one partner in the relationship than for the other). Evolution towards a common plan is just as rife among plants. The cactuses of the Americas - spiny, thick-skinned and globular - resemble the Euphorbias of South Africa, but have no more than a distant affinity to them.