While the others record disputes and debates, Dawkins opts for a detached, empyrean tone. Like the Pope on Catholic dogma, Professor Dawkins decrees ex cathedra (with overtones of infallibility) that biology is as he describes it. Each fossil has to be placed in context and milked for maximum information. Although astonishing information can be gleaned from the slightest specimens, there are gaps in the fossil record as there are in the historical record. These gaps offer ample space for personal interpretation - and therefore for dispute and contention.Oddly, virtually none of this appears in Richard Dawkins's account of evolution, Climbing Mount Improbable (Viking, pounds 20). Evolutionary biology in general does not depend on the fossil record - Darwin's "origin of species" does not rely on arguments deriving from fossils - but it does require the mute testimony of the rocks and the fossils, just as the historian requires written historical records.

A chemist or a physicist can go back to the laboratory to repeat and refine an experiment; a biologist cannot replay the evolution of Homo sapiens. Like cosmology, that other surrogate religion, evolutionary biology has more in common with history than with conventional experimental science. It is a strength of Shreeve's book that it displays this human side of science rather well.For the truth is that there is room for doubt, opinion and polemic in science - in evolutionary biology perhaps more so even than in other scientific disciplines. Wolpoff, however, believes that the transition proceeded in parallel right across the planet. Both sides have defended their view not just by appeal to "objective" evidence, but also by partisan showmanship far removed from the lay understanding of how science is conducted. What is at issue is how Homo erectus evolved into Homo sapiens. Did it happen in Africa all over again, but this time a few hundred thousand years ago, rather than a few million?According to this idea, promulgated by Chris Stringer, anatomically modern humans originated in Africa and migrated out to populate the entire globe.

No one now disputes that Homo erectus was the transition between ape-like creatures and the human lineage, and that Homo erectus spread out of Africa to populate the entire globe. He presents a fascinating insight into the intense personal animus that can develop between scientists as they passionately debate the origins of modern humans.The point at issue is the "Out of Africa" hypothesis. In the late 20th century, passions fly between Chris Stringer, of the Natural History Museum in London, and Milford Wolpoff, of the University of Michigan, as Shreeve's book shows. The Dutchman Eugene Dubois discovered the first evidence of the missing link in Java towards the end of the 19th century, but no one would believe him, and Dubois's passionate intensity turned almost to paranoia.

Only after all this has been done it is possible to address the intellectual puzzle of what it all means.Both books are good, too, on the human passions and human failings of science and scientists. The Nariokotome Boy lacked not just the capacity to speak, but to think.Part of the excellence of these two books lies in the way they show science in the making. Walker's book, co-written with his wife Pat Shipman, details the sheer physical labour involved in shifting tonnes of rock and earth to uncover fragmentary scraps of bone. Once the fragments are prised from the soil, a different sort of labour ensues as researchers struggle to piece them together like some frustrating jigsaw puzzle.