Before we can make much sense of evolutionary psychology we need to review some of the basics of evolutionary theory.

Darwin proposed during his life two evolutionary mechanisms. The first and central mechanism is natural selection. People often describe natural selection as "survival of the fittest." But this is not quite right. More precisely, fitness is defined as reproductive success (or, the differential survival of offspring). That is, you might be the smartest, fastest, or strongest animal on the savanna but if you have no offspring all that genetic talent dies with you. Generally, however, being smart, fast, or strong does tend to correlate with reproductive success, but, technically, those factors don't define Darwinian fitness.

What this means, and this will prove important throughout this series, is that natural selection is sexy. It's all about sex and children. That is the game. As I tell students, we are here today because each of our forebears got lucky.

But evolution is even sexier than this. There is a lesser known evolutionary mechanism which Darwin proposed in The Decent of Man, his follow-up to The Origin of Species. In The Decent of Man Darwin outlined the mechanism of sexual selection. If natural selection is the differential survival of offspring then sexual selection is differential mate choice.

Darwin posited sexual selection to explain odd features in the animal kingdom. Two prime examples are flamboyant coloration and the peacock's tail. Both of these traits appear to make the animal more vulnerable to predators. Flamboyant coloration compromises camouflage (think of the male cardinal) and the male peacock has to carry around that huge tail. In short, these features seem like handicaps. Why would natural selection not punish these frivolous traits?

Darwin posited that these features may persist because they are functioning as sexual signaling devices. That is, in species where males compete for mates, female choice exerts an adaptive pressure upon the males. If females lock on to a sexual signal (like bright coloration or a larger more colorful tail) this trait explodes creating a sexual ornament, a trait that attracts mates and signals genetic fitness.

It should also be noted that sexual selection does not just affect the morphology (i.e., bodies) of the species. It can affect behavior as well. Consider Ptilonorhynchidae, the bowerbird. You will recall that male bowerbirds build elaborate nests to attract female mates. The males with the better nests are selected, on average, more than others which amplifies the nest-building behavioral trait. Due to this amplification, sexual selection can move much faster than natural selection, quickly selecting and amplifying morphological and behavioral traits.

Let's apply some of these ideas, for the sake of illustration, to humans.

One of the great mysteries of human evolution is why we are so smart. We know when we became so smart. We just don't know why.

Specficially, the hominid fossil record shows that brain evolution exploded starting about 3.5 million years ago. That is, within about 3.5 million years we went from upright chimps (Australopithecus afarensis) to Homo sapiens. So that is the when. What about the why?

Well, for that kind of rapid growth SOMETHING powerful had to be selecting for increasing brain size. What was that thing? Most answers point to natural selection, suggesting that some environmental pressure selected for behavioral and cognitive flexibility which called for bigger brains. Most scenarios point to the fluctuating climate conditions during the last two million years. But it is hard to see how advancing or retreating ice sheets would create unique pressures upon on the human brain.

In contrast, some have speculated that the SPEED of brain evolution bears all the hallmarks of the trait amplification seen in sexual selection. That is, our brains grew in size because intelligence became the target of female mate choice. In this view, our brains are sexual ornaments. Like the color of the male cardinal or the peacock's tail, our brains are sexual signaling devices, informing potential mates of our genetic and behavioral fitness. Smart is sexy.

This is the thesis of Geoffrey Miller in The Mating Mind. I'd recommend the The Mating Mind as one of a handful of nice popular primers on evolutionary psychology. I don't know if Miller's thesis is wholly compelling, but it is very interesting.

And before we dismiss Miller's thesis too quickly, let us consider a new study out in the APA Journal of Personality and Social Psychology by V. Griskevicius, R. Cialdini, and D. Kenrick from Arizona State. Their study is entitled Peacocks, Picasso, and Parental Investment: The Effects of Romantic Motives on Creativity. This is a study on what the authors call the muse effect, an increase in creative display to attract or maintain the attention of a potential mate. Overall, across four studies this effect was observed (with some interesting differences between men and women). These findings are consistent with the The Mating Mind thesis: Creative displays (artistic and intellectual) are used as sexual ornaments. Think of Ptilonorhynchidae.

So perhaps this is why humans engage in so much exciting creative activity, artistically, kinetically, and intellectually. Creative intellectual acts may help signal fitness to potential mates. If so, the ability to create deep and rich theological structures may be a sexual ornament.

Maybe this is why theology is so sexy.