ALMOST CHIMPANZEE

If humans and chimpanzees share a 99 percent genetic similarity, why are we so different?

Science magazine correspondent Cohen (Coming to Term: Uncovering the Truth About Miscarriage, 2005, etc.) isn’t on an anti-evolution jag. He’s simply curious that a nearly identical molecular makeup doesn’t result in more identical organisms. Since Robert Yerkes’s Almost Human (1925), the similarities between humans and chimpanzees has been scrutinized, and for good reason—chimpanzees needed all the goodwill they could muster, or they would go extinct. Though chimpanzees still need protection, Cohen suggests that they would not be imperiled by exploring our genetic and behavioral differences to see what current chimpanzee research can tell us about that divergence. Thus starts a worldwide quest to witness that research at close range, from laboratories to the wild. The author’s enthusiasm is communicable and his writing is crystal clear. Even readers who have forgotten their biology will follow, for instance, his explanation of how the quantity of gene expression helps differentiate the two apes or the possibilities attendant upon non-coding ribbons of DNA regulating that expression. There is a jaw-dropping chapter on hybridization and how it could have played a part in the human-chimpanzee split as a bridge for genes across the species divide. (Much here is speculative, in a hard-science sense.) Cohen wades into work on sialic acid that may explain why a long list of infectious cancers and heart ailments more often afflict humans than chimpanzees. The author also examines how memory quality, sexuality and diet helped drive the behavioral wedge deeper between us. There is much conflict and turf-staking. A respected cognitive evolutionist says, “evidence has forced me to seriously confront the possibility that chimpanzees do not reason about inherently unobservable phenomena,” while a few pages earlier Cohen describes experiments with chimpanzees that “demonstrated that they could understand—to a degree—the psychological states of others.” Such is the “theater for intellectual daring” of chimpanzee behavioral theory that the author so ably delineates.

A lucid, entertaining synthesis of current research providing plenty of food for thought on why we took a different road from our kissing cousins.