Donald Griffin coined the word philosopause to describe those innumerable texts written by scientists towards the end of their careers to explain how their research has enlightened our understanding of the human condition. I have always been surprised how rather mundane lifetime contributions are dressed up in this way. I say this because it is important to emphasise that Paul Ehrlich's often anecdotal and very personal analysis of the human condition is not of the philosopause genre. Instead, it is the beautifully crafted work of a gifted scientist and proven communicator of science.
The aim of the book is to describe and analyse the roles of genes, environments and cultural transmission on how we have come to be and what our prospects are for the future. Paul Ehrlich was the ace doomsayer of the 1970s when, decades ahead of his time, he and Anne Ehrlich portrayed a miserable future of over-population, depleted resources and environmental degradation. That same zeal permeates this book, though the message is less despairing. He is willing to admit that even his own guarded pessimism for the future may be unjustified: cultural evolution might just take a new turn so that we are able to live in harmony with our environment for the foreseeable future.
The thrust of the book is to teach its reader those basics of evolutionary biology that are necessary to understand human genetic and cultural evolution and then to apply that imparted knowledge to unravel the past and paint scenarios for the future. Teaching genetics, the commonalities and differences between humans and other primates, and the determinants or degrees of cultural diversity can be dull. However, Ehrlich employs his experiences as a writer and as a scientist to make it a story that flows with captivating charm and unerring accuracy.
One trick he uses is to take three short experiences in his life to which he returns time and again as he weaves his tale. The first is how as a young evolutionary biologist he artificially selected fruit flies so that they became resistant to the insecticide DDT. The second is the summer of 1952 that he spent among the Inuit, who used a language and culture so different from his own. Finally, there is the trip he made to Gombe Stream Reserve, where he was privileged to watch Jane Goodall's chimpanzees acting naturally though habituated to the presence of human observers. Necessarily anecdotal, these experiences of genetic evolution in action, of cultural diversity and of the behaviour of our close living relatives illustrate many of the more general points that he needs to make. But Ehrlich's personal approach does not stop there: stories of his colleagues, friends, grandchild, wife, back pain and vasectomy are used freely to entertain and instruct.
What then of the book's substance? Put simply, the book is one long argument explaining why, when analysing humans from a biological and hence sociological perspective, we should do better to think in terms of human natures rather than human nature. The reasons for drawing that conclusion are not so very straightforward. After all, as we are instructed (or reminded), only a tiny proportion of known genetic variation among humans is restricted to particular geographic regions. The situation was sound-bitten by American population geneticist Richard Lewontin, who pointed out that 90 per cent of human genetic variation is present in native Africans. Indeed, if all humans were wiped out except one small cultural group, the Xhosa people who inhabit the tip of South Africa, 80 per cent of human genetic variation would be preserved. Another perspective on this same issue comes from our repeated failure to obtain an objective criterion for defining human races. The major problem is that features such as skin colour, hair structure, head shape and height do vary regionally, but they do not co-vary. In other words, moving from areas where skin colour is dark to where it is light tells us virtually nothing about how the other features change.
Even if genetic variation is not demarcated strictly among geographic regions, surely genes do influence behaviour? Ehrlich points out that the remarkable shortage of genes argues against a simplistic matching gene-for-behaviour model. The problem is that there are about 1 billion nerve connections per gene and, since nerve connections or synapses ultimately control behaviour, the genetic reductionist approach to explaining human behavioural responses is doomed. Nobody doubts that our genes influence our looks and behaviour one way or another, but accumulating evidence can leave us in no doubt that behavioural variation among humans is determined largely by variation in the cultural milieu experienced by individuals. That is the background against which Ehrlich embarks on his quest to bring us up to date on what scientists have learnt about the human condition.
True to his training, Ehrlich's perspective is unashamedly evolutionary. He takes us through a course on genetical evolution through natural selection, and how one or a few ancestral species give rise to adaptive radiations of many species such as the cichlid fishes of African lakes, or the Galapagos Island finches that were first recognised by Darwin. Given the necessary biological background, we learn with astonishing simplicity and economy of language exactly what is known about the ancestry of modern humans. Our family tree from 5 million years ago to the present is described in the context of the reasons why we were probably selected to look different from our forebears. I say "probably selected", because, while the bones exist in situ, the behavioural characteristics are lost to inference.
Ehrlich's text of a little over 300 pages is supplemented with a further 100 pages of detailed notes and references that provide the pros and cons of particular arguments, and refer the reader to more specialist literature. And in his role as a populariser of science, Ehrlich is quite unusual in keeping up to date with research advances over the vast span of human sociobiology covered by this book.
From morphological evolution, we are led to cultural evolution. We learn how stone tools and other components of culture evolved as we migrated around the world (from diagrams in the book, I identified an Acheulean stone axe I excavated last summer). We find out what is special and what is ordinary about the human brain. We are introduced critically to the reasons why religion and incest are thought to be so near to human universals, while chance historic events or contingency mean that so many other behavioural beliefs and practices have arisen sporadically during human history. We may be shocked by what we learn about human sexual practices. We may even come to believe that evolution has something to tell us about the origins of ethics, football hooliganism and mass murder. But most of all, any one of us reading this book will start thinking in new ways about things we had neatly packaged in our mind as either solved or insoluble.
Ehrlich's wit recurs throughout to give unanticipated but refreshing breaks in the narrative. Rather than spoil the fun in store, let me recount a typical Ehrlich moment. A friend of mine realised that Ehrlich had been in Sweden when the population changed from driving on the left side of the road to the right. When asked what happened, Ehrlich replied that it was all rather unexciting: one week you were driving on the left and the next you were driving on the right, with just a tricky transitional few days in between when you could drive on either side. As his book explains, the ways our minds evolved probably have set limits to cultural practices.
Paul Harvey is head of zoology, University of Oxford.
Human Natures: Genes, Culture and the Human Prospect
Author - Paul R. Ehrlich
ISBN - 1 55963 779 X
Publisher - Island Press
Price - £25.50
Pages - 531