Henry Gee’s big beef in The Accidental Species is with a common and popular narrative in which the evolution of man is a steadily unrolling tale of progress. Think of the classic image of a knuckle-dragging, ape-like creature giving way to a hunched, primitive man who in the following frames becomes taller and bolder until finally he looks like a Premier League football player minus the shorts. The truth, Gee argues in this amusing but baggy book, is much more complex and surprising.
Exhibit A is Homo floresiensis, a miniature woman whose fossilised remains were discovered in 2003 on the Indonesian island of Flores. Gee, a senior editor at Nature, sides with those scientists who judge “Flo” to be a direct descendant of the Australopithecus line rather than a shrunken form of a more recent member of our genus. If this view is right then a picture established over several decades in which only much more modern humans left Africa has to be cast aside. The case of Flo, says Gee, is his book in microcosm: “It shows how new discoveries often challenge deeply held notions of how we think evolution really ought to have happened.”
Gee stresses that the gaps in the fossil record are vastly bigger than the data points. This applies to the rest of life as much as to the history of our own species. “It is possible,” he writes, “that entire groups of unimaginably strange creatures have lived on this planet for millions of years but died out leaving no trace at all in the fossil record.” (Even creatures close to us, such as gorillas, have left no trace at all in the fossil record: had they been driven to extinction sooner than now looks likely, we might never have known of their existence.)
Recent discoveries continue to support Gee’s argument. The human family tree turns out to be very tangled indeed. Denisovans, only identified in 2010, mated not only with both our ancestors and Neanderthals but (scientists determined just this year) another mysterious population of archaic humans that lived in Asia more than 30,000 years ago that was neither modern human nor Neanderthal. “It begins to suggest that we’re looking at a Lord of the Rings-type world – that there were many hominid populations,” says Mark Thomas, an evolutionary geneticist at UCL.
“Nothing in biology makes sense except in the light of evolution.” You may never have heard of the Ukrainian-American geneticist and evolutionary biologist Theodosius Dobzhansky but it’s quite likely you have heard those words, and for good reason: the more evidence accumulates, the more firmly established his insight becomes.
This does not mean, however, that there are no puzzles left in evolution, and it is to many of those in the case of man, that strangest of creatures, that David Barash turns his attention in Homo Mysterious, out now in paperback from OUP USA (RRP £12.99, available from the Telegraph Bookshop for £11.99). These mysteries, to be clear, are not ineffable matters beyond the reach of understanding but rather aspects of our being for which a scientific explanation has not yet been agreed but where, following Dobzhansky’s dictum, one is surely possible.
The first half of Homo Mysterious focuses on physiological mysteries that are largely or entirely peculiar to humans among mammals. Why do women menstruate? Why do they have prominent breasts when they are not giving milk to young? Why is ovulation not displayed by a swollen bottom seen in many other primates? What purpose does female orgasm serve? How to explain homosexuality?
Barash, a professor of psychology and biology at the University of Washington, Seattle, explores the many and various answers proposed to these questions. By and large he succeeds admirably in explaining both the pieces of the puzzles and the strengths and weaknesses of solutions to date.
He also explores the evolutionary psychology underlying art, religion and human intelligence itself. Barash dissects various claims with clarity and wit. It is likely, he says, that natural selection, whether acting at the level of individuals or of groups (where tight social bonds promote survival), has been responsible for the existence and preservation of religion, and that religion has been adaptive for human beings, at least in the past.
Both Gee’s and Barash’s books are worth attention even though neither addresses the biggest mystery and challenge facing humanity: what sort of world are we making today?
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