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A Pilgrimage to the Dawn of Life
The Ancestor’s Tale
By Richard Dawkins
Phoenix Press, 2005, £9-99
ALONG DAWKIN’S pilgrimage we meet our ancestors, as other pilgrims join the journey. All life alive today gradually meets up. Each "most recent common ancestor" is welcomed and a tale is told.
Starting with humans we meet chimpanzees, apes and eventually fish, insects, fungi, plants and bacteria. There are 39 ‘rendezvous’ points (forks in the tree) at which point there is an ancestor (‘concestor’) common to both forks. A recurring theme is that starting with humans is only interesting because we are human. The journey could have started anywhere and we would have ended up in the same place at the same time about four million years ago. Life started once (but this will be qualified later).
Dawkins uses the opportunity to discuss recent work being done in the field of molecular biology. New methods and techniques are revealing sometimes surprising additions in our knowledge of evolution. Even if you are familiar with the ideas of evolution and natural selection there is plenty to interest you. It is fascinating to see how much progress has been made in deepening our understanding and is, at times, almost amusing to see that this can often lead to more disagreements not less. Previous certainties have to be revisited and reassessed. At the same time, there are still intriguing areas of uncertainty, especially the further back you go.
Dawkins is not neutral; he takes sides; he has opinions. He also sees no reason to ‘dumb down’. While accessibly written there is a considerable amount of detail which, on occasion for this reader, can be quite heavy going. His passion, enthusiasm and his genuine excitement about recent developments are infectious, however, and he takes you with him. It is a book you can read cover to cover but also go back to and read in parts. It would be useful as a reference. There are pointers to authors and books on the various questions if you need further information.
The "most recent common ancestor" does not mean the first. For humans it may not have been African. It may only be a few tens of thousands of years ago and it is also possible that none of her genes will have come down to us. Dawkins is sympathetic to the idea that humans did most certainly come out of Africa but may have done so two or even three times (see Out of Africa, Again and Again, by Alan Templeman). There is even evidence to suggest migrations back to Africa in between.
Different ‘tales’ raise questions about evolution. For instance, as we meet the different apes Dawkins asks: "Why do we walk on two legs?" "How did we lose our tail?" The Howler Monkey Tale includes a discussion on colour blindness and considers whether, in some circumstances, it may be an advantage.
Rendezvous eight is The Great Cretaceous Catastrophe, 65 million years ago, separating the age of mammals from the much longer age of dinosaurs – the last but not the biggest ‘mass extinction event’. We do not actually meet any dinosaurs as there are no surviving descendants. We do meet birds, a distant relative, but much later. Instead, we meet shrews and mice which were able to survive both the dinosaurs and the cataclysmic meteorite.
Here Dawkins delights again in pointing out that the mouse genome is, indeed, roughly the same size as the human genome, 30,000 genes, and is in many ways identical. Some people, he says, seem to find this "an offence to human dignity". Tackling the human-centric view of life ("the conceit of hindsight") is a theme he returns to again and again. It is the reason he started the journey in the present and worked backwards. Any special uniqueness of the human species is rapidly undermined. The concepts of higher or lower forms of life, primitive life-forms, dead ends and side branches are all firmly rejected and he quotes from the late Stephen J Gould who was well known for arguing this point. If it’s alive and wriggling, it works.
Sex frequently enters into the discussion. The Seal’s Tale addresses dimorphism, the relative size of the sexes. A male southern elephant seal can weigh in at four tonnes (heavier than a cow elephant) and four times the weight of the much smaller female. When the males fight, females and young pups can be crushed. How did this arise? What effect does it have on evolution? Who gets to mate with whom and how many? How do these factors affect humans? What are the effects of evolution on sex ratios? Many theories about why human beings "lost our hair" are linked to sexual attraction.
It seems that the question, Why sex? is still unresolved, with many competing and varyingly satisfactory theories. More worryingly, for some at least: Why males? The 160 species of bdelloids (microscopic freshwater worms) have managed asexually (only females – it can’t work for men) successfully for millions of years. The bdelloids raise another question. If species is defined as ability to mate successfully (in the wild) how does an asexual species evolve into other species?
The Salamander’s Tale (a newt) reveals one of the mechanisms of how species can evolve into another, a ring species. In California there is a valley with mountains along each side and across the top. At the bottom of the valley there are two species, one on each side of the valley. They cannot mate. While at the extreme ends of the valley they cannot mate, there is a succession of hybrids around the ‘ring’ (up one side, across the top and down the other) which can.
The answer to the question, can a female of one species give birth to another? The answer is no. Can you tell where one species ends and the other starts? Again, no, you can’t. There are two species of seagull where the same process can be seen but in their case the ‘ring’ stretches half way around the world and the gulls at each end of the ‘line’ look completely different.
Among many other questions, we are asked: Why did some fish leave the water and some other animals, like dolphins, ‘go back to the water?’ The closest relative of the hippo is the whale. This leads Dawkins to speculate that evolution may be quicker and a lot easier without the effects of gravity.
Dawkins rails against the seemingly innocuous phrase: "The whole is greater than the sum of the parts". He complains that, "the rhetoric of holistic harmony can degenerate into a kind of dotty, Prince Charles type mysticism. Indeed, the idea of a mystical ‘balance of nature’ often appeals to the same kind of airheads who go to quack doctors to ‘balance their energy fields’". Religion, religious people (especially bishops) get the same short shrift. He has said, "religious education is a form of child abuse".
The grand finale is, of course: how did life begin? Precisely how and when, obviously, cannot be known. We are given a review of the various work that has been done (starting in the 1920s) on the question. Laboratory experiments recreating the conditions on earth four billion years ago, plus some ‘lightning’, produce promising results. Dawkins argues that the key is not only reproducing, say, a cell but producing one that can reproduce a cell similar to itself – a cell that can be inherited from. But clearly there is a long way to go.
How many times did life start? Possibly more than once but only one life-source has left any descendants. Could it start again? Again, possibly, but it would most likely be eaten by bacteria! If life started again would it evolve the same way? Would we evolve? Not ruled out, but Dawkins thinks it unlikely it would get past the ‘complex cell’ stage.
Will we continue to evolve? He does not know – and is tired of being asked! He helpfully points out that 99% of all species that have evolved have become extinct – we may be the first species to arrange our own mass extinction!
This is an excellent contribution to the debate. A sometimes tough, but gripping read. This is not a dry academic work but a lively and at times impassioned polemic. There is plenty here for everyone to have a good argument about.