Science: Chaucer's 'Canterbury Tales' are the inspiration for an exploration of mankind's connections with other species, writes Dick Ahlstrom.
Many people still have a problem with the notion, irrefutable given modern science, that we are related in the distant past to chimps and gorillas. How disconcerting for these same people to read Richard Dawkins's latest book, in which he highlights our common ancestry still further back with amphibians, tube worms and single-celled organisms.
The Ancestor's Tale is an audacious book, a monumental work that takes us back in time to the origins of life on this planet. He provides us with a time machine that winds back the clock and brings us to the dawn of life and the first organisms to arise in the primordial soup that fostered them.
As a Renaissance man, and in common with his earlier writings such as Unweaving the Rainbow, Dawkins imposes a literary theme on the book, this time Chaucer's Canterbury Tales. Like Chaucer's pilgrim characters who depart in the April showers, Dawkins brings the reader on a pilgrimage to the past, passing milestones along the way.
His, however, are junctions of a different sort, the points in the distant past where one species's family tree joins that of another. The beings found at these points of common ancestry he renames using the word "concestors", a term he generously acknowledges to Nicky Warren.
About six million years ago (mya) it was the chimps and 14 mya the gibbons. We have to retrace our steps to 75 mya to reach the concestor linking us to rodents, a point, he notes, that is perhaps 15 million generations ago or a concestor equivalent to our "15- million-greats-grandparent".
This is Dawkins's pilgrimage, a march back through time to the source. Along the way we collect other pilgrims, concestors also in search of their origins. "If we retrace our own ancestral steps, we shall inevitably meet these other pilgrims and join forces with them in a definite order, the order in which their lineages rendezvous with ours, the order of ever more inclusive cousinship," he writes.
This is his mission, to show us our connections with other species on this planet, using just about every scientific discipline available to tell his story. There is biology, genetics and biochemistry of course but also botany (yes we are also related to plants), microbiology (and germs), and virology (and viruses). Yet there is also geology as he describes plate tectonics and how species can become genetically isolated, and archaeology, as he piles up the evidence for his arguments about evolution and how it works. He even takes on explanations about weather and how climate affected species as they lived out their lives on this changing planet.
As ever, Dawkins writes in a most lucid and accessible style, always understandable and engaging. He doesn't preach, he just tells the story and the reader benefits from the wealth of information provided.
Weighing in at almost two kilos, the book has the look and feel of a coffee table book. Yet while it does offer lavish illustrations that are pleasing to the eye, this book is really all about the words and the story and how scientists, using DNA and other evidence, have demonstrated our kinship with the organisms with which we share this earth.
Of particular note are the wonderful full-page colour plates that grace the beginning of each "chapter", defined by Dawkins rather as "rendezvous" with each concestor grouping. They show an artist's impression of what our concestor of the time might have looked like in its natural habitat.
There is also a useful graphic showing the branches of the tree of life as they merge to form larger limbs and common paths. The upward end of each limb sports thumbnail pictures indicating the variety in each concestogrouping.
Rendezvous 17 is with the amphibians, 340 mya, where we have a common "175-million-greats-grandparent". Here, a variety of creatures join including frogs, toads, salamanders and caecillans.
At Rendezvous 26, more than 500 mya, it becomes more difficult to find fossils to help make the scientific case. Not so, says Dawkins, who describes how "molecular rangefinding" provides a technique to help establish kinship.
In keeping with Chaucer, Dawkins allows species all along the route back in time to have a say and state their case. Rendezvous 26 includes the Grasshopper's Tale, which "treats the vexed and sensitive topic of race", he writes. "The Grasshopper's Tale is about races and species, about the difficulties of defining both, and what all this has to say about human races." Grasshoppers are loathe to breed across species, he points out, yet humans readily breed across what we erroneously define as species as indicated by skin colour. He makes his point using recent photos of President Bush and members of his administration including Condoleezza Rice, Colin Powell and Donald Rumsfeld. We all recognise Powell and Rice as "black", yet Powell is as "white" as Bush and somewhat whiter than Rumsfeld in the same picture.
Zoologists define a species as a group whose members breed with each other, he says. "We might dispute whether this is the only sensible definition of a species, but it is the definition that most biologists use." Genetics also shows us that the human species, whatever the colour, is "especially uniform" so what sense can be made of our powerful sense of race?
Eventually we reach the last Rendezvous, with concestor 39. We see this single-celled prokaryote organism floating with its neighbours in a non-descript world, the soup mentioned above. We have marched back an astonishing 3.5 billion years in a pilgrimage well worth the taking.
The Ancestor's Tale: A Pilgrimage to the Dawn of Life By Richard Dawkins. Weidenfeld & Nicolson, 528pp. £25
Dick Ahlstrom is Science Editor of The Irish Times