In 1970 Chris Stringer was a young graduate hoping to find a post to work for a Ph.D on the Neanderthals, but was having no luck in getting funding and was thinking of giving up his temporary job at the Natural History Museum to go to a teachers' training college. At the last moment a Medical Research Council post came up at Bristol University. Still impecunious, and desperately anxious to see Neanderthal skulls, he set off in July 1971 to drive through Europe in a battered old car and visit museums. This book is, in a sense, the outcome of that journey, for it led Stringer to become one of the leading advocates of the theory that modern humans emerged fairly recently from Africa and replaced the existing types of Homo they found in the rest of the world.
The book starts by summarizing the present state of knowledge about human evolution. The authors emphasize the existence of major puzzles. Fossils found in China, tentatively dated about 350,000 years old, have much large brain cases than Homo erectus. These are either individuals who evolved locally and rapidly from H. erectus or are examples of archaic H. sapiens who migrated into the region, in which case wide population dispersals must have been occurring. Even more puzzling is the 1936 discovery at Ngangdong of H. erectus bones that may be only about 100,000 years old. Finally, there is the enigma of the Neanderthals, on whom much of the discussion focuses.
Although Stringer is a firm advocate of the Out of Africa hypothesis for the origin of modern man, he acknowledges certain difficult questions. If there were primitive modern humans in Africa 100,000 years ago, why did they take so long to reach Europe, Asia, Australia, and the Americas? We know very little about this crucial period. There seems to have been a bottleneck, when only a small number of our ancestors survived, but what caused it? And what drove the subsequent expansion in populations?
Another set of questions concern our relatively wimp-like physique. Why are we so gracile? Probably we were beginning to replace brawn with brain for the first time in human evolution, but there is much here that is guesswork. One curious observation is that there has been a trend towards smaller body size since the time of the Cro-Magnons (even our brains are smaller). This change is often attributed to the invention of agriculture, which supposedly made it unnecessary for us to be so robust; but the trend is already evident in Australian hunter-gatherers. Indeed, it isn't just humans who were getting smaller; in Europe, both hunter and prey have been shrinking over the past ten millenia. Probably the explanation is climatic change, although one researcher has suggested that the position of the Earth in its elliptical orbit may be responsible by causing alterations in gravity and electromagnetism.
We also need to find explanations for our present physical appearance. Why do we have head hair; why do men have beards; why do both sexes have axillary and pubic hair? The authors suggest adaptational explanations for these features, and only hint at sexual selection, which seems to me likely to have been important.
The evidence for the African origin of modern humans does not rest entirely on fossils. As is well known, it also depends on mitochondrial DNA, and this is discussed. Another chapter takes up the theme and claims that we are all 'Africans under the skin'.
This is a fascinating and very readable exposition of the African hypothesis. It is in some ways a sequel to Stringer's previous book (In Search of the Neanderthals); if you enjoyed that book you will like this one as well.