Sexual selection and novelty

(written by lawrence krubner, however indented passages are often quotes). You can contact lawrence at:, or follow me on Twitter.

There is a whole lot of good books coming out about Darwin. The Times gives the longest treatment to the one that focuses on sexual selection. Richard Dawkins apparently makes an idiot of himself again. He was on the cutting edge in 1976, when he wrote The Selfish Gene. Have you read it? It’s a great book. It’s really more about game theory than genes, or perhaps I should say it is about applying game theory to genes. He’s got some great examples though, about insects and fish and birds and other kinds of life. But a lot has changed since 1976, in math and game theory. Back then it was thought possible that you could use a utility function to model natural selection. And you can. But you can’t use a utility function to model evolution. That natural selection can not model all of evolution has become more and more clear over time. I forget who, but some mathematician was able to prove that as a search space gets wider, it becomes more and more likely that a utility function will get stuck in a local optimum, rather than the global optimum. When a search space is infinite, a utility function becomes useless — you would have sort through infinite data to find the global optimum. And what is the search space of all life, and everything life has faced, over 4 billion years on Earth? It is a damn big search space, which limits the usefulness of utility functions. Lately game theorists have been obsessed with novelty functions, and how they get incredibly better results if they combine a novelty function with a utility function. To my mind, there is a close link between the combination of novelty-function/utility-function and the combination of sexual selection and natural selection.

This is a bit from the article:

Bowerbird males provide Prum some of his most convincing examples. These remarkable birds woo their potential mates by constructing circles, cones, or maypole-like structures out of twigs, then ornamenting both the structures and the ground within and around them with stones, shells, beetle cases, colorful fungi and other found art. Both the architecture and the male’s behavior invite the female to observe and consider while leaving her both the space to do so and a clear escape path. In some bowerbird species the male laboriously arranges and rearranges his display, examining it from various angles and making small fixes, writes Prum, with the care of a “fussy florist.” The males of several species observe the female examining their work while half-hidden behind a tree or some fencelike part of the bower. If she likes what she sees, she stretches her neck and raises her tail in invitation, and the male comes to mate. (This takes only seconds, and the two will never meet again.) If she doesn’t, she leaves.

Prum believes these and similar courtship appeals in other species have arisen from a long, multigenerational, co-evolutionary conversation between mating partners. The male’s aesthetic and social qualities are repeatedly tested, judged and (through selection) modified according to whether they please potential mates. Thus the females’ individual preferences, says Prum, help drive evolution.

Like all selection, this is not intended to reach any particular goal; it just unfolds according to the demands of either fitness, or in this case, beauty. A trait selected for its beauty, of course, might create problems by selecting for ornaments that work against fitness. But, most crucially in the end, and often offsetting these problems, this “aesthetic” courtship, says Prum, creates an environment, temperaments and rituals — a sort of culture — that give the female sexual choice, autonomy and safety. (As noted, she doesn’t get everything; once she and the male mate and part, she raises the offspring by herself.)

Prum sees such aesthetic choices as driving a gradual “aesthetic remodeling” — an evolutionary reshaping of mating behavior, and even of male social behavior more widely, by the civilizing pressure of female preference. Prum stresses this is not about emasculating males, or dominating them; it’s simply about selecting for males who allow females autonomy and choice.

By this point in the book, Prum, having made his case so well in birds, turns to the implications of sexual selection for Homo sapiens. He nimbly mines both the animal and human literature to show how, for one human trait after another, adaptationist explanations miss the mark while aesthetic explanations hit home. His catalog of Things Natural Selection Can’t Explain but Sexual Selection Easily Can includes homosexuality, a tendency toward monogamy, both sex’s taste and capacity for sex outside of female fertility periods, the deweaponization of the human male through the evolutionary shrinkage of almost every body part except the brain and the evolution of human paternal care, which is highly unusual among our fellow apes and close primate cousins. To name just a few.

Consider, for instance, this handful of well-known distinguishing human traits: our constant interest in sex, permanent breasts, big penises, and, last but hardly least, women’s orgasms. Except for constant sexual interest (and possibly female orgasm) in bonobos, none of these traits evolved in our fellow ape species. Prum argues that they evolved in humans because they help women evaluate men’s prosocial-pleasure potential. When sex offers orgasm at relatively low pregnancy risk, it provides a way not just to reproduce but to assess potential mates’ attention to female desires, tastes and choices. Essentially, Prum says, humans evolved to negotiate and have sex as a sort of display ritual. The boudoir is our bower.

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