the evolving mind

In some circumstances the application of evolutionary-psychology thinking can be as silly as trying to find the primate precursor to the behavior of a piloting an airplane. Did swinging from trees help prepare humans for steering a Boeing 747 through 3-dimensional skies? Isn’t it obvious that peeling a banana is the antecedent to opening a flight log?

In future posts I will address questions about just how scientific evolutionary psychology is and can be (section titles: “Science and the Educated Guess,” and “Indirect Evidence and Possible Tests”). But putting that very-important issue aside right now, there is an essential question begging to be asked: Why the heavy focus on chimpanzee behavior?

There are a couple reasons for this.

First, chimpanzees are the most and best studied of the non-human primates. Second, DNA analysis has found that of any species, Pan troglodytes is most genetically similar to Homo sapiens.

But wait. The bonobo, or Pan paniscus, is as closely related to us as are chimps. It seems. While chimps and humans have a between 1 and 2% dissimilar genetic material, chimps and bonobos — a cousin species of the chimp, previously called the “pygmy chimp” — have approximately .3% non-shared genes. Because bonobos are usually lumped in with chimps, it is difficult to determine whether one or the other is a closer genetic kin to us. At least one biologist, Alison Jolly of the University of Sussex, has concluded that the bonobo is “no closer” to the human than is the chimpanzee.(1) Triglodyte or paniscus: Will the truer proto-human please stand up?

It is my present belief that chimpanzee behavior provides greater insight into human behavior. The late Roger Gould saw it this way, too:

“Inasmuch as morphologies can be interpreted correctly as reflections of behavior, therefore this suggests that the common ancestor was likely to have been more chimpanzee-like than bonobo-like in aspects of its behavior that were correlated with cranial development.” (2)

Of course, human beings are ultra-adaptive, if ultra-anything. I have previously argued that human nature could be compared to a Swiss Army knife. What is our true nature? Well, it depends upon the task at hand. Under some conditions we may be more triglodyte-like, in others, paniscus-like.

But wait. Recent research has suggested that the better primate to use as a guide to human nature is . . . the orangutan.

Rather than relying on genetic analysis, researchers John Grehen and Jeffrey Schwartz looked at physical characteristics of primates to draw conclusions about our family tree and the nearness of the branches of other species.

Schwartz and Grehan scrutinized the hundreds of physical characteristics often cited as evidence of evolutionary relationships among humans and other great apes-chimps, gorillas, and orangutans-and selected 63 that could be verified as unique within this group (i.e., they do not appear in other primates). Of these features, the analysis found that humans shared 28 unique physical characteristics with orangutans, compared to only two features with chimpanzees, seven with gorillas, and seven with all three apes (chimpanzees, gorillas, and orangutans). Gorillas and chimpanzees shared 11 unique characteristics. (3)

Physical characters that our kind more closely share with orangutans include thickly enameled teeth.

Should the orangutan now stand out as the go-to species for evolutionary psychologists? Probably not. More research is needed. But the orangutan-hypothesis clearly exposes the sketchy state of our current knowledge.

Back to the chimp-bonobo face-off. The greatest challenge to using chimp behavior as the best source of clues to human primate evolution comes from the bonobo. A number of experts have been arguing for some time that the relatively pacifist, “make love not war,” seemingly egalitarian bonobo is a better psychological match to our kind.

By focusing on the chimp am I thus painting an inaccurate picture? Maybe so, even with the proviso provided by my Swiss Army knife analogy. But maybe not. One thing is for sure: the bonobo question is important enough to further explore.

—

(1) Jolly, A. Lucy’s Legacy, Harvard University Press, Cambridge, MA, 1999.
(2) Gould, R. V. Collision of Wills: How Ambiguity About Social Rank Breeds Conflict, University
of Chicago, Chicago, 2003, p.6
(3) John R. Grehan and Jeffrey H. Schwartz, “Evolution of the second orangutan: phylogeny and biogeography of hominid origins,” Journal of Biogeography, 2009

Technorati Links: evolutionary psychology, primatology

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