Understanding the elemental foundation of evolutionary psychology is as simple as pondering this question:
Why do we ride horses, but not zebras?
One of the tricky parts about evolutionary psychology research is that we don’t have a surviving species to which we can compare Homo sapiens in a closely analogous way. With the divergence between us and the rest of the extant primate species dating to 6 million years ago, comparisons to our closest relatives effectively suffer from 12 million years of divergent evolution. Of course, comparisons with species as far away from us as fruit flies yields insight, so there’s still a lot to work with. Obviously, comparisons of brain development and function between humans and fruit flies is… um… lacking. The best tool we have for studying evolved human psychology is the difference between males and females. Besides the political resistance associated with this approach, it’s limited in that human males and females faced the same ecological pressures. Indeed, even when comparing humans to other apes over evolutionary time, we’re still making comparisons to species which evolved in Africa. The worst thing to happen to evolutionary psychology was the extinction of Homo neanderthalensis.
To the best of our knowledge, modern humans were confined to the African continent until 40K-50K years ago. As such, most of our unique evolution was influenced by a “tropical” (in the geographic sense, not the balmy islands stereotype) ecology. The numbers aren’t concrete, but estimates of the divergence between humans and Neanderthals have been placed in the range of 800K years. We know that interbreeding took place much later than that, and it appears that Neanderthals were a distinct species at 300K years ago. The reason their extinction is unfortunate for the study of evolutionary psychology is that they were bipedal primates with a very similar brain size who likely evolved for hundreds of thousands of years in the more northern climates Europe and western Asia. Thus, we had an almost perfect speciation experiment for comparison of the African Homo line to the Euro/Asian Homo line during Middle-Upper Paleolithic. Ironically, it’s been hypothesized that humans are responsible for the extinction of Neanderthals. Whether that was an ancient conspiracy by nurture biased social scientists to make evolutionary psychology more difficult to study… we may never know. 😉
Fortunately for the quick and easy analogy applicable to evolutionary psychology, the zebra (H. sapiens analogue) did not drive horses (H. neanderthalensis analogue) to extinction. Modern horses and zebras diverged earlier (by millions years) from their common ancestors, but it was still during the ecologically relevant Pleistocene (paleolithic). Another component of the Homo – Equus analogy is that modern horses evolved in northern latitudes while zebras evolved in Africa. What were the results?
Casting aside discussions of differences in stripes, speed, size, et cetera, we have one huge difference between zebras and horses: Horses can reliably and predictably be domesticated, zebras cannot. They evolved different temperaments which influence their behavior at the species level. In fact, there are nearly a dozen species of African zebra, all of which share the characteristic of being resistant to domestication. Something about the environment in which they evolved drove natural selection toward a skittishness that didn’t evolve in modern horses. The common hypothesis for this difference is the difference in predators between the horse’s evolutionary environment and the zebras’ evolutionary environment. The constant and intense pressure on zebras by numerous big cats (and that’s only the beginning) put them on constant alert. It’s no surprise that being on constant alert would have been evolutionarily advantageous. Zebras with slow reaction times were ancestors to Fancy Feast®. While predation of horses certainly existed as well, climate and its impact on food sources applied different pressures on them. For the sake of the hominid – equine analogy, it isn’t necessary (though it is an interesting question) to draw parallels between predation and temperament. Indeed, the extinction of Neanderthals makes it difficult to test this hypothesis. What is important for a fundamental understanding of evolutionary psychology is that evolving within a different ecology will lead to different strategies being imprinted in the brain; differences that will show through in behavior.
From a human aesthetics and psychological battlefield intimidation standpoint, it’s interesting to ponder why “send in the cavalry” doesn’t evoke images of boldly striped beasts. If anyone tries to tell you that psychology can’t evolve in a way that impacts behavior, implore them to go ride a zebra.