People generally write about human evolution with one of two approaches: they aim to explain who we are now, with the past as a support; or they seek to look at that past in detail in its own right, with separate value in each part of the story. Kim Sterelny appears to have started with the first, but in The Pleistocene Social Contract, he seeks explicitly to elucidate that earlier record. Sterelny is a philosopher of biology, but his book could be cast as a thorough evaluation of human evolution by a social psychologist with a deep interest in primatology: the actual labels do not matter very much, because the study of human evolution is so interdisciplinary, and its students must often make their own expertise. Sterelny's focus on free riders, kinship, ritual, and religion certainly places him in the social camp of scholarship on these topics. His exploration centers on two main themes: the building of culture and the development of cooperation. Neither theme is new in the literature, but Sterelny adds to them his central idea of the Social Contract, and in a rapidly changing area of study, there is going to be a great deal to both evaluate and say.
The text provides a straightforward outline of hominin evolution, not textbook style, but full enough that scholars from other areas of social sciences or biology will find their footing. Interestingly, his investigation of a long time depth has an unusual balance. He acknowledges the length of the early phases, and the importance of bipedalism, but he does not discuss Ardipithecus or the bewildering variety of australopithecines or their ecology. And at the later end, dealing with higher levels of cognition and cooperative behavior, he scarcely mentions the symbolism and art that dominate so much writing. He does treat the first building of cumulative culture: he covers issues of hunting in a good deal of detail, the major cultural developments that we see in Oldowan and Acheulean tool kits, and the use of fire. He reads importance into their elaboration step by step over a long period—evidence of the “culture-building” that helps to underpin human distinctiveness. How then does he work a way forward toward later humans, quite refreshingly eschewing the traditional “symbolic” route? He looks at mechanisms of society and the evidence for them, most apparent in scaled-up technologies for hunting; he stresses drive lines and such features as large-scale fish traps in aboriginal Australia. These do not reach deep into the Pleistocene, but they do seemingly go back to Neanderthal times (as shown by La Cotte de St Brelade in Jersey).
Rather than giving site-level details of the paleoanthropological record or other proxies, Sterelny is deeply concerned with forms of cooperation, transitions in behavior, and the importance of communication. Humans have come to occupy an apex predator niche, but this transition would not be possible without a level of cooperation not seen in our great ape cousins. Language is a part of this, treated here as a necessity for more complex adaptations in technology, as well as for ritual or even communication in hunting. One piece of evidence he picks out—among the more extensive networks of cooperation—is that humans recognize far more kin than do any related species. The difficulty, of course, with these lines of argument is that they swing us inexorably toward later times, when we can be surer that language did exist. It is beyond the scope of the book to tease out the detail of tiny things that might tell us that complex language did or did not exist in the more distant past. The different hominins, too, are brought into groups—habilines, erectines, and even Heidelbergensians—with a broad brush. With new finds, such enveloping labels get increasingly difficult for hominin paleontologists, but some simplifications are necessary for telling the story at all.
How did hominin differentiation begin? This working out of beginnings is challenging, and similar issues occur with group size and violence—closed and open groups. Sterelny is more comfortable with ideas set out by Robert Layton and Sean O'Hara, who postulate increased hominin hunting as encouraging cooperation, than those of Richard Wrangham and colleagues, who use interpretations of chimp models of closed groups and violence to help interpret human violence. As Sterelny notes, “The hominin situation is very different from that of chimps, and this reshapes the costs and benefits of permanent hostility” (p. 113), but at some initial point, the hominin situation had to begin to become different, or chimp ancestors to have different behavior. And one irony is that in both humans and chimps the cooperation is sometimes directed toward goals of violence.
Toward the end of his account, Sterelny broaches the topic about which most has been written: the Neolithic Revolution and its consequences. Here, his Social Contract—often implicit rather than explicit in the book, despite its title—comes to the fore. The author grapples with the complexities by listing key points before formulating two key questions: (1) How and why did egalitarian forager communities sometimes become unequal hierarchical societies? (2) Why did cooperation and collective action survive that change? He goes on to explore these at length, but to my mind, he hits the nail on the head immediately when he points out that even in small egalitarian societies, there is a constant need for policing of individuals who yearn for power and wealth.
There are several concise accounts of human nature and evolution in compact books. It is not unfair to make a snapshot comparison with two other recent volumes. Roger Scruton is another philosopher looking at human nature, emphasizing human distinctiveness, and looking at selection (On Human Nature, Princeton University Press, 2017) but not working through the past as Sterelny does. Ian Tattersall gives a bare-bones overview, a physical anthropology with behavioral insights (but no fraction of the social analysis provided by Sterelny) in his book Understanding Human Evolution (Cambridge University Press, 2022). Sterelny notes that his own interests have developed since about 2000, and he carves his way into the issues largely but not entirely as studied in the new century, fully up-to-date on the new “cultural biology.” In sum, this book has a valuable place for all those who want to think hard about the challenges overcome in hominin evolution. Even if this landscape is broadly familiar, one emerges with the feeling of having been given a tour by a very good guide, seeing places from new angles, and having yet more to think about.
