Backwards in time
Until now histories of life, in particular human life, usually start at its far beginnings, and work forward. This produces a certain attitude of mind. From infinitely small humble origins developed the amazing creature which is ourselves. Was it all for us? Was the process divinely ordered? Was it a concatenation of chances? Or was it simply a product of natural selection operating under familiar Darwinian rules? If so, could comparable creatures be found on other planets on similar orbits round similar suns?
The answers to some of these questions can be found more easily if we reverse the process, and work backwards from what we already know. In his lavish new book, Richard Dawkins uses three main methods for tracing life in the past: analysis of fossils, the visible but incomplete and often enigmatic relics of ancient ecosystems; renewed relics, ranging from oral and written records to the DNA in the cells of our bodies; and triangulation by which he means comparing the development of different organisms and their overlapping DNA to establish the measure of common origin.
By these methods Dawkins conducts a pilgrimage into the past. As in the Canterbury Tales, different pilgrims tell different tales at different stages or points in the journey at which their ancestry converges: what Dawkins calls "Rendez-vous" where "concensors" or common ancestors meet. Such pilgrims cover a wide spectrum: from our near ancestor Cromagnon man and Eve herself to lampreys, sponges and even cauliflowers. As the President of the Royal Society reminds us from time to time, we share 40% of our genes with bananas.
It seems well established that we are not descended from the Neanderthal people with whom our ancestors lived side by side until around 30,000 years ago, but we certainly share descent from a concensor. Some of the genes the concensor bestowed went to both sorts of human. I remember once seeing a man on the London Underground the shape of whose head and shoulders seemed classically Neanderthal. I had to quench my curiosity and refrain from walking round and round him. Dawkins makes an important point in this respect. Common evolutionary descent involves gene trees not genealogical trees: in other words it is our genetic composition not our individual ancestry that counts. In his own words:
"An itinerant selfish gene
Said 'Bodies a-plenty I've seen.
You think you're so clever
But I'll live for ever
You're just a survival machine.' "
Dawkins establishes 39 Rendez-vous for his survival machine, each a little less certain than its predecessor. A key one for us as mammals was 65 million years ago when an extra terrestrial object of several kilometres diameter hit the coast of what is now Yucatan in Mexico. The distribution of land and sea world wide was then very different, and of course has changed enormously over the 4 billion years or so of life. By ridding the earth of the long standing dynasty of the dinosaur family, the impact opened the way for the proliferation of mammals deriving from shrews of many varieties into a diversity of niches including that now occupied by ourselves.
Beyond Rendez-vous 8 some 70 million years ago the pilgrims' tales have a fairy tale quality. As Dawkins puts it, our 150 million greats-grandmother might have looked something like thrinaxodon (an early vertebrate of the cynodont family). Then he goes further back beyond the first multicellular creatures to eukaryotes, thence to prokaryotes, thence to eubacteria, archaea and eukarya, and finally to the still mysterious first living cell.
A fundamental issue is why living organisms evolved the way they did. The late Stephen Jay Gould saw it as a series of contingencies. If we wound back the tape of life, and changed, even slightly, the starting conditions, then the results could have been very different. As Andrew Knoll once put it, "travel another path, and life's history is a gripping tale of cyanobacterial survival, a cautionary tale of trilobitic fall, or the inspirational story of yeasts finding sustenance in rotting fruit".
Against this is the view that the development of organisms, however different in origin, tends to converge in response to their environment: thus the resemblance between ichthyosaurs, fish and whales. Dawkins gives a particularly good account of these arguments. He quotes Mark Twain: "history doesn't repeat itself, but it rhymes". As for life elsewhere, or indeed its possible origin from elsewhere (for example in the panspermia ideas of the late Fred Hoyle), we do not know and may never do so. What we do know is the incredible interlinked interdependent complexity of living creatures which has caused some to see the earth as a kind of superorganism.
In this book Dawkins brings together many of the ideas he has put forward elsewhere into a coherent and elegant whole. The device of travellers' tales enables him to branch out in many directions. He looks at racism among humans, pours happy scorn on creationists, has a crack at the turpitudes of Bush and Blair, and like a true pilgrim brings fun as well as learning to the journey. Evolution may have no foresight, but its manifestations have rarely been better explained. Read about the vulnerability of the dodo, the different size of chimpanzee and gorilla testicles, the peculiarities of the monotreme, the neoteny of the axolotl, and the growth of what he calls "eukaryocracy" or lordship of the eukaryotes (although the bacteria in and around us may have the last laugh).
The book with its big shiny pages is beautifully illustrated with imaginative reconstructions by Malcolm Godwin, and helpful graphs throughout. It is not a book to read in bed. It weighs a lot and almost needs a desk for easy reading. Its central philosophy is well stated on the last page. Pilgrimage implies reverence. Such reverence should go to "the sublime grandeur of the real world".
