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

by Richard Dawkins

This is the ‘anthropic’ notion that the very laws of physics themselves, or the fundamental constants of the universe, are a carefully tuned put-up job, calculated to bring humanity eventually into existence. It is not necessarily founded on vanity. It doesn’t have to mean that the universe was deliberately made in order that we should exist. It need mean only that we are here, and we could not be in a universe that lacked the capability of producing us. As physicists have pointed out, it is no accident that we see stars in our sky, for stars are a necessary part of any universe capable of generating us. Again, this does not imply that stars exist in order to make us. It is just that without stars there would be no atoms heavier than lithium in the periodic table, and a chemistry of only three elements is too impoverished to support life. Seeing is the kind of activity that can go on only in the kind of universe where what you see is stars.

Perhaps, argue some physicists such as the Nobel Prize-winning theorist Steven Weinberg, the fundamental constants of the universe, which at present we treat as independent of one another, will in some Grand Unified fullness of time be understood to have fewer degrees of freedom than we now imagine. Maybe there is only one way for a universe to be.

The theoretical physicist Lee Smolin added an ingenious Darwinian spin which reduces the apparent statistical improbability of our existence. In Smolin’s model, universes give birth to daughter universes, which vary in their laws and constants. Daughter universes are born in black holes produced by a parent universe, and they inherit its laws and constants but with some possibility of small random change—‘mutation’. Those daughter universes that have what it takes to reproduce (last long enough to make black holes, for instance) are, of course, the universes that pass on their laws and constants to their daughters. Stars are precursors to black holes which, in the Smolin model, are the birth events. So universes that have what it takes to make stars are favoured in this cosmic Darwinism.

cannot find a physicist to condemn the theory as definitely wrong—the most negative thing they will say is that it is superfluous. Some, as we saw, dream of a final theory in whose light the alleged fine-tuning of the universe will turn out to be a delusion anyway. Nothing we know rules out Smolin’s theory, and he claims for it the merit—which scientists rate more highly than many laymen appreciate—of testability. His book is The Life of the Cosmos and I recommend it.

In a backward chronology, the ancestors of any set of species must eventually meet at a particular geological moment. Their point of rendezvous is the last common ancestor that they all share, what I shall call their ‘Concestor’:

If every fossil were magicked away, the comparative study of modern organisms, of how their patterns of resemblances, especially of their genetic sequences, are distributed among species, and of how species are distributed among continents and islands, would still demonstrate, beyond all sane doubt, that our history is evolutionary, and that all living creatures are cousins. Fossils are a bonus. A welcome bonus, to be sure, but not an essential one. It is worth remembering this when creationists go on (as they tediously do) about ‘gaps’ in the fossil record. The fossil record could be one big gap, and the evidence for evolution would still be overwhelmingly strong.

the DNA alphabet is a four-letter alphabet. Many vital sections of DNA spell out three-letter words from a dictionary limited to 64 words, each word called a ‘codon’. Some of the codons in the dictionary are synonymous with others, which is to say that this genetic ‘code’ is technically ‘degenerate’.

The dictionary maps 64 code words onto 21 meanings—the 20 biological amino acids, plus one all-purpose punctuation mark.

A ‘sentence’ of codons specifying one protein molecule is an identifiable unit often called a gene.

the great statistician and evolutionary geneticist Sir Ronald Fisher anticipated these startlingly recent dates. He wrote the following, in a letter dated 15 January 1929 to Major Leonard Darwin (Charles’s second youngest son): ‘King Solomon lived 100 generations ago, and his line may be extinct; if not, I wager he is in the ancestry of all of us, and in nearly equal proportions, however unequally his wisdom is distributed.’

You’d have to be barking mad to think that ‘selfish’ genes really have deliberate intentions to survive! We can always translate back into respectable language: the world becomes full of those genes that have survived in the past. Because the world has a certain stability and doesn’t change capriciously, the genes that have survived in the past tend to be the ones that are going to be good at surviving in the future. That means good at programming bodies to survive and make children, grandchildren and long-distance descendants.

an individual organism can be a universal ancestor of the entire population at some distant time in the future, yet without passing on a single bit of her DNA to that population!

For any piece of DNA (‘gene’), you are equally likely to pass on the version you inherited from your father or that from your mother. Just by chance, you could happen to give all your mother’s versions to your child, and none of your father’s. In this case, your father would have given no DNA to his grandchild.

if you have any European ancestors at all, you can probably trace at least one line back to Charlemagne, 40 or so generations ago. On average, only one trillionth (2 to the power 40) of your genome will have come through that particular line. But there are only 3 billion actual letters in your genome! The average amount of DNA inherited via this route would appear to be only a tiny fraction of a single DNA letter.

D. K. Belyaev and his colleagues took captive silver foxes, Vulpes vulpes, and set out systematically to breed for tameness. They succeeded, dramatically. By mating together the tamest individuals of each generation, Belyaev had, within 20 years, produced foxes that behaved like Border collies, actively seeking human company and wagging their tails when approached.

Molecular evidence clearly shows that all modern breeds of dog are descended from the grey wolf, Canis lupus.*

Perhaps initially, wolves took to scavenging around human encampments. Humans may have found such scavengers a convenient means of refuse disposal, and they may also have valued them as watchdogs, and even as warm sleep comforters.

From the wolf’s point of view human camps provided rich pickings for a scavenger, and the individuals most likely to benefit were those whose serotonin levels and other brain characteristics (‘propensity to tameness’) happened to make them feel at home with humans. Several writers have speculated, plausibly enough, about orphaned cubs being adopted as pets by children.

Lactose, the sugar in milk, requires a particular enzyme, lactase, to digest it. (This terminological convention is worth remembering, by the way. An enzyme’s name will often be constructed by adding ‘-ase’ to the first part of the name of the substance on which it works.)

around 50,000 years ago. Here human society, entirely consisting of hunter-gatherers, underwent what may have been an even larger revolution than the agricultural one, the ‘cultural Great Leap Forward’.

50,000 years. Something happened then—many archaeologists regard

After the Leap, all these things suddenly appear in the archaeological record, together with musical instruments such as bone flutes, and it wasn’t long before stunning creations like the Lascaux Cave murals were created by Cro-Magnon people

It can mean lots of things to different people, but when I talk about genes in the context of ‘gene trees’ I mean a distinct sequence of DNA that has been passed intact down the generations.

Whenever we have two types, the rarer of which is favoured because it is rare, it is a recipe for polymorphism: the positive maintenance of variety for variety’s sake.

In fact, the genes responsible for the A and B blood types probably diverged before our split with the Old World monkeys, around 25 million years ago. This feature of evolution is called trans-specific polymorphism, and it shows conclusively that differences between humans can trace back to before humans themselves existed.

We can make an even more stunning deduction.

For certain genes, you must be more closely related to some chimpanzees than to some humans. And I am closer ...

It has been suggested that human/Neanderthal offspring, especially males, may have experienced fertility problems, which could also explain why we see less Neanderthal ancestry among genes that are mainly switched on in the testis. If this is true, our Neanderthal ancestry traces back mostly through hybrid women, not men.

A modern European contains on average about 1.2 per cent Neanderthal DNA, a modern Asian about 1.4 per cent, and Africans have almost no neandergenes.

They are named after the Denisova Cave in the Altai mountains of Siberia,

We might expect a similar pattern to Neanderthals, who are known to have lived in Siberia too. Modern Eurasians, remember, have inherited a small but significant fraction of Neanderthal DNA. In contrast, apart from one group, modern humans show very little Denisovan DNA. The exception lies way to the south-east in . . . Oceania! Yes, thousands of miles from Siberia, and in a radically different climate, today the greatest density of Denisovan DNA is found in native Australians, New Guineans and Filipinos, and to a lesser extent in Polynesians and west Indonesian islanders. We’re not just talking tiny quantities either: it can be up to 8 per cent of the genome.

It emerges that deliberately built campfires magnetise the soil in a way that distinguishes them from bushfires and from burnt-out tree stumps—I don’t know why. But such signs provide evidence that Ergasts, both in Africa and Asia, had campfires nearly one and a half million years ago.

All considerations of the origin of language begin by citing the Linguistic Society of Paris which, in 1866, banned discussion of the question because it was deemed unanswerable and futile. It may be difficult to answer, but it is not in principle unanswerable like some philosophical questions.

A family codenamed KE suffers from a strange hereditary defect. Out of approximately 30 family members spread over three generations, about half are normal, but 15 show a curious linguistic disorder, which seems to affect both speech and understanding. It has been called verbal dyspraxia, and it first shows itself as an inability to articulate clearly in childhood. Some authorities think the problem largely stems from co-ordinating rapid movements of the face and mouth. Others suspect the problem lies deeper, since it affects comprehension and written language too. What is clear is that the abnormality is genetic. Individuals either have it or they don’t, and it is associated with a mutation of a gene, present in all vertebrates, called FOXP2. This gene encodes a ‘transcription factor’: a protein which binds onto other DNA and switches on and off other important genes, in this case in various parts of the brain. The particular mutation in the KE family disrupts this binding. It is fortunate that the affected individuals have a second, normal copy of FOXP2 inherited from their other parent. Fortunate, because experiments have shown that mice which have two similarly mutant copies die very young, probably as a result of brain, lung and movement defects. This clearly shows that FOXP2 is not simply a ‘gene for language’, as it is sometimes touted in the press. Nevertheless, the evidence of the KE family suggests that in humans FOXP2 is important for the development of some par...

Back another million years from Homo ergaster, 2 million years ago there is no longer any doubt in which continent our genetic roots lie. Everyone agrees, ‘multiregionalists’ included, that Africa is the place.

Habilines mark the place in our history where the brain, that most dramatic of human peculiarities, starts to expand.

This distinction, indeed, is the rationale for placing the Habilines in the genus Homo at all. For many palaeontologists, the large brain is the distinguishing feature of our genus.

It is true that when we look at living species, we expect members of different genera to be less alike than members of different species within the same genus. But it can’t work like that for fossils, if we have a continuous historical lineage in evolution. At the borderline between any fossil species and its immediate predecessor, there must be some individuals about whom it is absurd to argue, since the reductio of such an argument must be that parents of one species gave birth to a child of the other. It is even more absurd to suggest that a baby of the genus Homo was born to parents of a completely different genus, Australopithecus.

The strength of a muscle is proportional not to its volume but to its cross-sectional area. This is because muscular movement is the summed movement of millions of molecular fibres, sliding past each other in parallel. The number of fibres you can pack into a muscle depends upon the area of its cross-section (second power of linear size).

The main conclusion is that, as animals get larger or smaller in evolution, we positively expect their shape to change in predictable directions.

Plot the logarithm of brain mass against the logarithm of body mass for lots of species of different sizes. The points will probably fall around a straight line, as indeed they do in the graph here. If the slope of the line is 1/1 (brain size exactly proportional to body size) it will suggest that each brain cell is capable of servicing some fixed number of body cells. A slope of ⅔ would suggest that brains are like bones and muscles: a given volume of body (or number of body cells) demands a certain surface area of brain. Some other slope would need yet a different interpretation. So, what is the actual slope of the line? It is neither 1/1 nor ⅔ but something in between. To be exact, it is a remarkably good fit to ¾. Why ¾? Well, that is a tale in itself, which will be told, as you will no doubt have guessed, by the cauliflower (well, a brain does look a bit like a cauliflower). Without pre-empting the Cauliflower’s Tale, I will just say that the ¾ slope is not special to brains, but crops up all over the place in all sorts of living creatures, including plants like cauliflowers. Applied to brain size, and with the intuitive rationale that must wait for the Cauliflower’s Tale, this observed line, with its ¾ slope, is the meaning we are going to attach to the word ‘expect’ as it was used in the opening paragraphs of this tale.

The human brain is ‘too’ big, even by the standards of primates, and the average primate brain is too big by the standards of mammals generally.

Harry Jerison, the father of fossil brain size studies, proposed an index, the Encephalisation Quotient or EQ, as a measure of how much bigger, or smaller, the brain of a particular species is than it ‘should’ be for its size, given that it is a member of some larger grouping, such as the vertebrates or the mammals. Notice that the EQ requires us to specify the larger group which is being used as the baseline for comparison.

turns out that the modern human brain is about six times as big as it should be, for a mammal of equivalent size

I think inflationary evolution demands a special kind of inflationary explanation. In Unweaving the Rainbow, in the chapter called ‘The Balloon of the Mind’, I developed this inflationary theme in a general theory of what I called ‘software-hardware co-evolution’. The computer analogy is with software innovations and hardware innovations triggering each other in an escalating spiral. Software innovations demand an escalation in hardware, which in turn provokes an escalation in software, and so the inflation gathers pace. In the brain, my candidates for the kind of thing I meant by a software innovation were language, spoor-tracking, throwing, and memes.

Could the enlarged human brain, or rather its products such as body painting, epic poetry and ritual dances, have evolved as a kind of mental peacock’s tail?

Reminding people that we didn’t evolve from chimpanzees can be tediously repetitive. It is actually rather a relief to find evidence indicating that, in a few important ways, our common ancestor need not have resembled either a chimp or a gorilla.

did our ancestors benefit from the skill of walking on two legs because it freed their hands for carrying food—perhaps back to a mate or children, or to trade favours with other companions, or to keep in a larder for future needs?

Incidentally the latter two possibilities may be closer to each other than they appear. The idea (I attribute this inspired way of expressing it to Steven Pinker) is that before the invention of the freezer the best larder for meat was a companion’s belly. How so? The meat itself is no longer available, of course, but the goodwill it buys is safe in long-term storage in a companion’s brain. Your companion will remember the favour and repay it when fortunes are reversed.* Chimpanzees are known to share meat for favours. In historic times, this kind of I.O.U. became tokenised as money.

Any male who feeds a nursing female accelerates the weaning of her current child and brings her into receptiveness earlier. When this happens, she might make her receptiveness especially available to the male whose provisioning accelerated it. So, a male who can bring lots of food home might gain a direct reproductive advantage over a rival male who just eats where he finds. Hence the evolution of bipedalism to free the hands for carrying.