The Ancestor's Tale: A Pilgrimage to the Dawn of Evolution

by Richard Dawkins

John Reader in his fascinating biography of Africa, suggests that upright posture minimises exposure to the sun, limiting it to the top of the head which is consequently furnished with protective hair. Moreover, when the body is not hunched close to the ground, it can lose heat more rapidly.

Kingdon visualises something similar in our ape ancestors in the forest, turning over stones or leaf litter for insects, worms, snails and other nutritious morsels. To do this effectively they would have had to undo some of their adaptations to living up trees. Their feet, previously hand-like for gripping branches, would have become flatter, forming a stable platform for squatting on the haunches. You will already be getting a glimmering of where the argument is going. Flatter, less hand-like feet for squatting are later going to serve as pre-adaptations for upright walking.

In former times it was possible to believe, as respected anthropologists did up to the 1960s, that the decisive evolutionary event that first separated us from the other apes was the enlargement of the brain. Rising up on the hind legs was secondary, driven by the benefits of freeing the hands to do the kind of skilled work which the enlarged brain was now capable of controlling and exploiting. Recent fossil finds point decisively towards the reverse sequence. Bipedality came first. Lucy, who lived long after Rendezvous 1, was bipedal, yet her brain was approximately the same size as a chimpanzee’s. The enlargement of the brain could still have been associated with the freeing of the hands, but the sequence of events was reversed. If anything it would be the freeing of the hands by bipedal walking that drove the enlargement of the brain.

Theory 4. Chimpanzees really could have passed through a more humanoid, bipedal stage before reverting to quadrupedal apehood. As it happens, this very suggestion has been revived by John Gribbin and Jeremy Cherfas, in their two books, The Monkey Puzzle and The First Chimpanzee. Although it is not a strictly necessary part of their theory, they even suggest that chimpanzees might be descended from gracile australopithecines (like Lucy), and gorillas from robust australopithecines (like ‘Dear Boy’). For such an in-your-face radical suggestion, they make a surprisingly good case. It centres on an interpretation of human evolution which has long been widely accepted, although not without controversy: people are juvenile apes who have become sexually mature. Or, putting it another way, we are like chimpanzees who have never grown up.

To summarise, the axolotl is an overgrown larva, a tadpole with sex organs. In a classic experiment by Vilém Laufberger in Germany, hormone injections persuaded an axolotl to grow into a fully adult salamander of a species that nobody had ever seen.

the prudent answer is that Concestor 1 was more like a chimpanzee, if only because chimpanzees are more like the rest of the apes than humans are. Humans are the odd ones out among apes, both living and fossil. Which is only to say that more visible change has occurred along the human line of descent from the common ancestor, than along the lines leading to the chimpanzees.

The especially interesting thing about nut cracking, termite fishing and other such chimpanzee habits is that local groups have local customs, handed down locally. This is true culture. Local cultures extend to social habits and manners.

In the Chimpanzee’s Tale we argued that the average divergence between human and chimpanzee genes traces back further than we once thought, to 10 million years ago or more. Yet at the start of this chapter we quoted a date for Rendezvous 1 of between 5 and 7 million years ago. This apparent contradiction is straightforward to explain. We have already seen that gene copies within a single interbreeding population (in fact even within your own body) can coalesce millions of years into the past. When a species splits into two, the genes in each population will carry with them a pre-existing history. That means splits between genes can predate splits between species by millions of years.

‘The chimpanzee resolves sexual issues with power; the bonobo resolves power issues with sex . . .’ Bonobos use sex as a currency of social interaction, somewhat as we use money. They use copulation, or copulatory gestures, to appease, to assert dominance, to cement bonds with other troop members of any age or sex, including small infants. Paedophilia is not a hang-up with bonobos; all kinds of philia seem fine to them. De Waal describes how, in a group of captive bonobos that he watched, the males would develop erections as soon as a keeper approached at feeding time. He speculates that this is in preparation for sexually mediated food-sharing. Female bonobos pair off to practise so-called GG (genital–genital) rubbing.

Over 70 per cent of our genes argue that chimps and bonobos are our closest relatives, not gorillas. And over 90 per cent of our genome affirms that common chimpanzees and bonobos are our equal cousins.

We say ‘daughter’ rather than son because of ‘Haldane’s rule’. The polymath J. B. S. Haldane, whom we shall meet at several points in this book, pointed out that in interspecies hybrids, if one gender is infertile, it is invariably the one with two different sex chromosomes. Thus in mammals, where the male has X and Y sex chromosomes, hybrids such as male mules are always infertile, whereas female mules (XX) can sometimes have normal babies. In birds and butterflies this pattern is reversed, because males are defined by their two Z chromosomes, whereas a W and a Z define a female. This pattern has long intrigued evolutionary biologists, particularly those interested in the origin of new species.

The Asian ape Gigantopithecus, a sort of giant orang utan, would have stood head and massive shoulders over the largest gorilla. It lived in China, and went extinct only recently, about half a million years ago, overlapping with Homo erectus and archaic Homo sapiens. This is so recent that some enterprising fantasists have gone so far as to suggest that the Yeti or Abominable Snowman of the Himalayas . . . but I digress.

Gorillas are entirely vegetarian. The males have harems of females. Chimpanzees are more promiscuous, and the differences in breeding systems have interesting consequences on the size of their testes

The Descent of Man that monkeys ‘smoke tobacco with pleasure’.

Nowadays, scientists not only think we resemble apes. We include ourselves within the apes, specifically the African apes. We emphasise, by contrast, the distinctness of apes, including humans, from monkeys.

tribes in both South East Asia and Africa have traditional legends suggesting a reversal of evolution as conventionally seen: their local great apes are regarded as humans who fell from grace. Orang utan means ‘man of the woods’ in Malay.

Perhaps we have been too ready to assume that our links with Africa go back a very long way. What if, instead, our ancestral lineage hopped sideways out of Africa around 20 million years ago, flourished in Asia until around 10 million years ago, and then hopped back to Africa?

The positive evidence in favour of the theory depends upon ‘parsimony’: an economy of assumptions. A good theory is one that needs to postulate little, in order to explain lots.

Parsimony is always in the forefront of a scientist’s mind when choosing between theories,

Any organ which is not used will, other things being equal, shrink for reasons of economy

In evolution, whether of animals or manuscripts, the most parsimonious explanation is the one that postulates the least quantity of evolutionary change. If two texts share a common feature, the parsimonious explanation is that they have jointly inherited it from a shared ancestor rather than that each evolved it independently. It is very far from an invariable rule, but it is at least more likely to be true than the opposite. The method of parsimony—at least in principle—looks over all possible trees and chooses the one that minimises the quantity of change.

Differences that are unique to a single manuscript, or a single species of animal, are uninformative.

since all genes are present in all cells, the difference between a red cone and a blue cone is not which genes they possess, but which genes they turn on. And there is some kind of rule that says that any one cone only turns on one class of gene.

The genes that make our green and red opsins are very similar to each other, and they are on the X chromosome (the sex chromosome of which females have two copies and males only one). The gene that makes the blue opsin is a bit different, and lies not on a sex chromosome but on one of the ordinary non-sex chromosomes called autosomes (in our case it is chromosome 7).

There are anecdotes of bomber crews in the Second World War deliberately recruiting one colourblind member because he could spot certain types of camouflage better than his otherwise more fortunate trichromat comrades.

Turning now to heterozygous advantage, the classic example—cliché almost—is sickle-cell anaemia in humans. The sickling gene is bad, in that individuals with two copies of it (homozygotes) have damaged blood corpuscles that look like sickles, and suffer from debilitating anaemia. But it is good in that individuals with only one copy (heterozygotes) are protected against malaria. In areas where malaria is a problem, the good outweighs the bad, and the sickling gene tends to spread through the population, in spite of the adverse effects on individuals unlucky enough to be homozygotes.

Although smaller than the size of your fist, a tarsier can jump more then 3 metres horizontally and 1.5 metres vertically.

Concestor 7 ran, hopped and scrambled in the trees, spending its small life in pursuit of insects. Of its two descendant lineages, one stayed in the light and blossomed into the anthropoid monkeys and apes. The other reverted to the darkness and became the modern tarsiers.

When I was a child of three in Nyasaland (now Malawi) we had a pet bushbaby. Percy was brought in by a local African, and was probably an orphaned juvenile. He was tiny: small enough to perch on the rim of a glass of whisky, into which he would dip his hand and drink with evident enjoyment. He slept during the day, clasping the underside of a beam in the bathroom. When his ‘morning’ came (in the evening), if my parents failed to catch him in time (which was often, because he was extremely agile and a terrific leaper) he would race to the top of my mosquito net and urinate on me from above. When leaping, for example onto a person, he did not exhibit the common bushbaby habit of urinating on his hands first. On the theory that ‘urine washing’ is for scent-marking, this would make sense given that he was not an adult. On the alternative theory that the urine improves grip, it is less clear why he didn’t do it.

Whut?

I don’t remember much from the discourse on lemurs that Harold Pusey—wise and learned warhorse of the lecture hall—gave to my generation of Oxford zoologists, but I do remember the haunting refrain with which he concluded almost every sentence about lemurs: ‘Except Daubentonia.’ ‘EXCEPT Daubentonia!’ Despite appearances, Daubentonia, the aye-aye, is a perfectly respectable lemur,

Aye aye

At Duke University, which surely has the largest collection of lemurs outside Madagascar, I have seen an aye-aye, with great delicacy and precision, insert the long middle finger up its own nostril—in quest of what, I don’t know.

Rendezvous 8, where our pilgrims meet the lemurs 65 million years ago, is the oldest rendezvous that takes place this side of the 66-million-year barrier, the so-called K/T boundary, which separates the Age of Mammals from the much longer Age of Dinosaurs that preceded it.* The K/T was a watershed in the fortunes of the mammals. They had been small, shrew-like creatures, nocturnal insectivores, their evolutionary exuberance held down under the weight of reptilian hegemony for more than 100 million years. Suddenly the pressure was released and, in a geologically very short time, the descendants of those shrews expanded to fill the ecological spaces left by the dinosaurs.

The Big Bang Model, in its extreme form, sees a single mammal species surviving the K/T catastrophe, a sort of Palaeocene Noah. Immediately after the catastrophe, the descendants of this Noah started proliferating and diverging. On the Big Bang Model, most of the rendezvous points occurred in a bunch, just this side of the K/T boundary—the backwards way of viewing the rapidly divergent branching of the Noah’s descendants. 2. The Delayed Explosion Model acknowledges that there was a major explosion of mammal diversity after the K/T boundary. But the mammals of the explosion were not descended from a single Noah, and most of the rendezvous points between mammal pilgrims predate the K/T boundary. When the dinosaurs suddenly left the scene, there were lots of little shrew-like lineages who survived to step into their shoes. One ‘shrew’ evolved into Carnivores, a second ‘shrew’ evolved into primates, and so on. These different ‘shrews’, although probably quite similar to each other, traced their separate ancestry deep into the past, eventually to unite way back in the Age of Dinosaurs. Those ancestors followed, in parallel, their long fuses into the future through the Age of Dinosaurs to the K/T boundary. Then they all exploded in diversity, more or less simultaneously, when the dinosaurs disappeared. The consequence is that the concestors of modern mammals long predate the K/T boundary, although they only started diverging from each other in appearance and way of life after th...

Doubt and uncertainty may seem rather unsatisfactory as the moral for a tale, but it is an important lesson that must be taken on board before our pilgrimage to the past proceeds much further.

Capybaras are prized for meat, not just because of their large size but because, bizarrely, the Roman Catholic Church traditionally deemed them honorary fish for Fridays, presumably because they live in water.

Unlike the case of mice and men, this is not a genetic difference, for your cells have essentially identical DNA. The difference is ‘epigenetic’—outside of the genome. This has been known since before the discovery of DNA—the word was coined by Conrad Waddington in 1942—but it has become disappointingly popular to trumpet this as something unexpected, even as a threat to our conventional understanding of genetics. Newspapers state with ill-informed astonishment that ‘new’ research shows the environment can modify which genes are turned on and off. Well of course it can! Embryology depends on it. And it’s not just when switching between different types of cell. Compared to a couch potato, we would expect a body builder to have a different pattern of genes being switched on in his muscles. Responding to environmental cues—be those hormones in embryonic development or external influences in an adult—is exactly what genes do. This has been known since Jacob and Monod’s investigations of bacteria in the early 1960s. And wasn’t it obvious even before?

Selfishness and co-operation are two sides of a Darwinian coin. Each gene promotes its own selfish welfare, by co-operating with the other genes in the sexually stirred gene pool which is that gene’s environment, to build shared bodies.

Genes in every cell of a beaver behave as if they ‘know’ what kind of cell they are in. Skin cells have the same genes as bone cells, but different genes are switched on in the two tissues.

Any consequence of a change in alleles, anywhere in the world, however indirect and however long the chain of causation, is fair game for natural selection, so long as it impinges on the survival of the responsible allele, relative to its rivals.

have seen a remarkable film of captive beavers imprisoned in a bare, unfurnished cage, with no water and no wood. The beavers enacted, ‘in a vacuum’, all the stereotyped movements normally seen in natural building behaviour when there is real wood and real water. They seem to be placing virtual wood into a virtual dam wall, pathetically trying to build a ghost wall with ghost sticks, all on the hard, dry, flat floor of their prison. One feels sorry for them: it is as if they are desperate to exercise their frustrated dam-building clockwork.

behaviour—the symphony of muscular contractions that is behaviour—this too is a perfectly respectable phenotype.

Differences in building behaviour are without doubt manifestations of differences in genes. And, by the same token, the consequences of that behaviour are also entirely allowable as phenotypes of genes. What consequences? Dams, of course. And lakes, for these are consequences of dams (see plate 9). Differences between lakes are influenced by differences between dams, just as differences between dams are influenced by differences between behaviour patterns, which in turn are consequences of differences between genes. We may say that the characteristics of a dam, or of a lake, are true phenotypic effects of genes, using exactly the logic we use to say that the characteristics of a tail are phenotypic effects of genes.

Conventionally, biologists see the phenotypic effects of a gene as confined within the skin of the individual bearing that gene. The Beaver’s Tale shows that this is unnecessary. The phenotype of a gene, in the true sense...

‘Laurasiatheria’ is as awkward as it sounds. It unites highly disparate mammals which have only one thing in common: their pilgrims all join up with each other more recently than the point at which they join us.

Within the mammals the order Carnivora does appear to be a genuinely monophyletic clade: that is, a group of animals, all descended from a single concestor who would have been classified as one of them. Cats (including lions, cheetahs and sabretooths), dogs (including wolves, jackals and Cape hunting dogs), weasels and their kind, mongooses and their kind, bears (including pandas), hyenas, wolverines, seals, sea lions and walruses, all are members of the laurasiatherian order Carnivora, and all are descended from a concestor which would have been placed in the same order.

Hippos’ closest living relatives are whales.

On their backward journey, the hippo pilgrims and the whale pilgrims unite with each other more recently than the two of them join the ruminants, and it seems that the other even-toed ungulates such as pigs and camels join them yet deeper in time.

suspect that major new departures in evolution often start in just such a way, with a piece of lateral thinking by an individual who discovers a new and useful trick, and learns to perfect it. If the habit is then imitated by others, including perhaps the individual’s own children, there will be a new selection pressure set up. Natural selection will favour genetic predispositions to be good at learning the new trick, and much will follow. I suspect that something like this is how ‘instinctive’ feeding habits such as tree-hammering in woodpeckers, and mollusc-smashing in thrushes and sea otters, got their start.*

If whales are glorified hippos, we are glorified lungfish. The emergence of legless whales from within the middle of the artiodactyls, leaving the rest of the artiodactyls ‘behind’, should not seem more surprising than the emergence of four-legged land animals from one particular group of fish, leaving those fish ‘behind’.

The true cost to a parent of making a child is measured in lost opportunities to make other children.