THUMBS, TOES, AND TEARS

Walter (Science Writing/Carnegie Mellon Univ.) celebrates Vive la différence—not so much between the sexes as between us and other primates.

The author recaps early hominid history on African savannas, detailing how a change in the position of the big toe (facing forward and not sideways) enabled not only upright posture but facility in movement. The opposable thumb in turn was the nifty mutation that led to a tool-making tradition. Now add neoteny, the delay in development so that adult forms of a species retain some infantile characteristics. In the case of Homo sapiens, neoteny means that babies are born highly immature, a painful compromise made necessary to allow the baby’s head to pass through a birth canal narrowed by the change to upright posture. These are twice-told tales, which Walter narrates with flair and enthusiasm, often relating the anatomical change to behavior. In the case of babies, there is a need for extended periods of parental care and nurturing, with all that implies about social bonding, securing a helpful mate and so on. For the rest of the book, Walter embarks on less familiar, more speculative ground. Clearly, language is a distinguishing human characteristic, which depends anatomically on a unique change in the position of the larynx in relation to the pharynx and the tongue, but whether gestures or grunts or both were precursors is not clear. Then it’s on to laughter, self-consciousness, tears and kissing: Here, Walter trots out numerous behavioral studies, brain imagings, evolutionary psychology research and anthropological lore to illustrate theories of why the behaviors developed. In general, Walter sees these activities as means of strengthening communication in a species dependent on social interaction. Alas, by the end, he is all too ready to spout arguments on sex differences that parrot ex–Harvard president Lawrence Summers, as well as the bits about males sowing their seed whenever they can, while choosy women look for male power and support.

Lively writing throughout—just take some of it with a grain of salt.