By Deborah Blum
Sunday, September 12, 2010; B06
Searching for What Makes Us Human, in Rainforests, Labs, Sanctuaries, and Zoos
By Jon Cohen
Times. 369 pp. $27.50
During the early 1920s, the pioneering primatologist Robert Yerkes kept two young chimpanzees -- cleverly named Chim and Panzee -- at his home to observe them in a human environment. He became particularly attached to Chim (later identified as a bonobo), admiring the animal's obvious intelligence and generous nature. When Panzee became ill, Chim actively tried to comfort and care for her. Yerkes described this behavior in a 1925 book he titled "Almost Human," although he admitted that he worried about "idealizing an ape."
It has been years, decades really, since researchers worried about idealizing chimpanzees or emphasizing their similarities to ourselves. The shift is largely credited to the fieldwork and educational activism of another pioneering scientist, Jane Goodall. Indeed, as Jon Cohen points out in his gently provocative new book, "Almost Chimpanzee," the conservation-minded Goodall deliberately dwelled on people-parallels. "She believed that a critical mass of humans would most likely come to her cause if they imagined their own hands reaching for the curl of a chimpanzee's finger."
But today, Cohen suggests, it may be time to dwell again on our differences. Chimpanzees are well established as our closest cousins on Earth; some research sets the genetic difference at a mere one percent. On the other hand, even that slight deviation set us on widely divergent evolutionary paths and, in the end, provided only one species with real power over life on Earth. "Humans will determine the fate of chimpanzees," Cohen notes. "Chimpanzees of course will have no say in the fate of humans."
Cohen's book, then, is a meticulous exploration of how both small quirks and large kinks in biology and culture led to such different destinations. He searches for the best evidence of when human and chimpanzee ancestors first separated -- usually fixed at about five million years ago -- and whether it was a genuinely dramatic break. He mulls over why small genetic variances have such enormous impact, leading him into a wonderfully weird discussion of whether human-chimpanzee hybrids are possible -- a notion dubbed "humanzees" by some researchers.
In a chapter called "Carnal Knowledge," Cohen delves further into human vs. chimpanzee reproduction, comparing everything from essential body parts to fertility issues. For instance, while healthy human males produce an average of 66 million sperm per milliliter, chimpanzees apparently clock in closer to an average of 2.5 billion. "Logically enough, higher sperm counts require larger testicles," he writes, citing evidence that the ratio is 3:1 in favor of chimps.
A long-time correspondent for the journal Science, Cohen has a gift for unearthing small and telling details. At the same time, he occasionally falls into a research-publication style of storytelling which undermines his effectiveness. When I read a sentence such as "Surface molecules on chimpanzee erythrocytes, in contrast, have loads of Neu5Gc and a sprinkling of Neu5Ac," I tend to look for my science dictionary rather than marvel over the facts in question.
But "Almost Chimpanzee" is not intended as a literary meditation on our place in the natural world (I had somewhat expected that based on the searching-for-ourselves implication of the subtitle). It is, instead, a briskly told, clear-headed survey of research that looks at the innate differences between two closely linked species, never forgetting that one of those species -- at least for now -- stands as the most successful primate in the planet's history.
There's a terrific section on life expectancy built around the evolutionary biology work of University of Utah anthropologist Kristen Hawkes that neatly connects everything from chimpanzee menopause to the role of elderly females in hunter-gatherer societies. And there's a fascinating look at the importance of cooking food, which allowed early humans to spend less energy sleepily digesting their dinners and more, apparently, devising a route to world domination.
All of this leads to the ever-troubling question of what comes next. Many scientists working with chimpanzees in labs find their studies restricted or too expensive to maintain over the long term. And many conducting field research wonder how much longer the animals will last as a wild species, because of habitat loss, poaching and the notorious African bush meat trade. One scientist whom Cohen interviewed predicted that within 50 years only captive chimpanzees will be left alive, almost entirely due to the activities of their human cousins.
Out of this gathering cloud of dismay comes one of my favorite quotations in the book, a description of a dedicated and cynical conservationist. "He's seen so many disgusting people," explains one of his friends, "and so few disgusting chimps." It's not meant to be a measure of all humans, but it definitely works as a measure of how far we've come from the time of Yerkes, when a scientist might hesitate to idealize apes but never ourselves.
Deborah Blum is a Pulitzer-Prize winning science writer and the author of two books about primate research, "The Monkey Wars" and "Love at Goon Park."