The Pequod Review:
Richard Dawkins’s eighth book, The Ancestor’s Tale, is a tour de force that traces the evolutionary history of human existence in a Chaucer-like way — beginning with the present day and proceeding backward through our common ancestor species (“concestors”) over the past four million years.
Backward chronology in search of ancestors really can sensibly aim towards a single distant target. The distant target is the grand ancestor of all life, and we can’t help converging upon it no matter where we start — elephant or eagle, swift or salmonella, wellingtonia or woman. Backward chronology and forward chronology are each good for different purposes. Go backwards and no matter where you start, you end up celebrating the unity of life. Go forwards and you extol diversity.
It works on small timescales as well as large. The forward chronology of the mammals, within their large but still limited timescale, is a story of branching diversification, uncovering the richness of that group of hairy warmbloods. Backward chronology, taking any modern mammal as our starting-point, will always converge upon the same unique ur-mammal: shadowy, insectivorous, nocturnal contemporary of the dinosaurs. This is a local convergence. A yet more local one converges on the most recent ancestor of all rodents, who lived somewhere around the time the dinosaurs went extinct. More local still is the backward convergence of all apes (including humans) on their shared ancestor, who lived about 18 million years ago. On a larger scale, there is a comparable convergence to be found if we work backwards from any vertebrate, an even larger convergence working backwards from any animal to the ancestor of all animals. The largest convergence of all takes us from any modern creature — animal, plant, fungus or bacterium — back to the universal progenitor of all surviving organisms, probably resembling some kind of bacterium…
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': the focal rodent or the focal mammal or the focal vertebrate, say. The oldest concestor is the grand ancestor of all surviving life.
The book’s structure is sometimes a bit awkward (the opposite direction may have worked better) and the discussions of each specific species often become repetitive, but in many ways this is Dawkins’s most detailed and complete work.