This book should be read by anyone with an interest in human evolution but especially by those with an interest in human uniqueness. Dr. Hrdy writes beautifully, is vigorous in her attention to empirical evidence, but she is also willing to speculate about the conditions that fostered uniquely human traits. Among the most obvious of these traits are our extended lifespans, prolonged childhoods, big brains, perspective taking (mind reading) or intersubjectivity, language use, cumulative culture, mutual understanding, norm formation and enforcement, altruistic punishment, and moral judgment. The list could of course go on but what concerns Professor Hrdy more than these individual traits is describing the conditions or preconditions fostering these co-evolving traits. As she notes, the most common explanation for our pro-social traits is group competition but, as she argues, such competition is common among other primates, especially the Great Apes, and the question becomes "why us and not them?" She does not discount completely the role of group competition but argues that by far the most important reason that humans display their uniquely pro-social suite of traits is that "novel [child] rearing conditions among a line of early hominins meant that youngsters grew up depending on a wider range of caretakers than just their mothers, and this dependence produced selection pressures that favored individuals who were better able at decoding the mental states of others, and figuring out who would better help and who would hurt" (p 66).Hrdy argues that cooperation more than competition accounts for our unique traits, although the two are hardly incompatible.
Dr Hrdy speculates that within the genus Homo, Homo erectus may well have exhibited cooperative breeding--that is, groupmates or alloparents other than mothers tended to children, including nonkin--and that they may have been emotionally modern. By 1.8 million years ago Homo erectus was almost as large and as large brained as Homo sapiens, and, although male australopithecines were twice as large as females, males and females among Homo erectus were only slightly more dimorphic than Homo sapiens. Whatever the precise date for the emergence of cooperative breeding within our line, humans, unlike any of the Great Apes, have cooperative breeding and this fact Dr Hrdy maintains is the precondition that made the remarkable human suite of traits possible.
In these brief comments I have stressed the speculative features of Dr. Hrdy's argument because they are both the most novel and interesting elements. Let me stress in conclusion, however, that the author attends scrupulously to data and evidence, so even if one is less convinced than I am about the theoretical claims she makes, the book will instruct the reader on every page, especially if it is read slowly.
Brad Lowell Stone