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defined
a posterior
rather than
a priori
. Beth may have married Bud despite his dandruff, but the genes that caused Bud’s flakes may later, when expressed in Bud’s and Beth’s baby, bestow on that kid immunity to some disease. Bud may have married Beth because of her freckles, but the genes for those winsome flecks may later predispose Beth’s and Bud’s kid to get some illness no one would wish on a friend. The good or bad consequences of a gene, then, are a matter of chance. Accordingly, sex, in Darwin’s theory, has the statistical consequence of quickening chance effects. Were there no sex (or were there sex with only oneself) the opportunity for genetic diversity would be low.
    Sex or, more specifically, competition for mating provides a forum to show off features that, as far as the participants can tell, bode well for survival. 8 In humans, clear skin may signal resistance to infection, a firm butt may signal strength, and a capacity for cool dance moves may signal agility. It’s rare for physical or behavioral features that prospective mates find appealing to be obviously
bad
for survival. They may not be especially
good
for survival once history runs its course except insofar as they are useful for attracting mates. Peacock plumes are the paradigmatic example of sexual attractants with an advantage other than attracting mates. Basso voices in human males may be another. 9 Breasts in human females may also serve that function, for lactation in other mammals comes without swollen mammaries. 10
Some More from Evolutionary Biology
    The Darwinian drama of individuals finding themselves more or less able to spawn offspring is a drama whose future direction no one knows or needs to know. The reason is that it can run its course without a prior plan. Indeed, there may be no plan at all.
    This last point is of inestimable importance for the theory of cognition to come, especially because cognition is so much about predicting and planning. 11 Later in this book I will suggest that what we take to be plans are just activities of neural populations shaped in basically the same way as other biological populations. Believing that we have plans need not imply that plans
per se
exist in our minds. Plans could be internal responses to situations (stimuli) we encounter that in turn trigger behaviors we call voluntary, intentional, or, indeed, planned.
    Returning to evolutionary biology, scholars in that area of study have said much more about natural selection than I have here. My aim has just been to give the flavor of the Darwinian process in simple and, at times, fanciful terms.
    Speaking fancifully is not meant to diminish the sophistication of the tools used by evolutionary biologists and their colleagues to explore the dynamics of natural selection. Those tools include studying fossils, counting organisms with different features in different environmental niches, and developing mathematical models of real and artificial life forms. With such methods, it has been possible to confirm Darwin’s theory or, saying this another way, to show that Darwin’s theory can withstand efforts to disconfirm it. 12 Darwin’s theory has gained so much credibility that it is possible to say it is no more speculative than Newton’s theory of gravitation. 13
    Evolutionary biologists have also uncovered some phenomena of special interest for what’s to come in this book. I will discuss three of them here: (1) the founder effect, (2) punctuated equilibrium, and (3) niche opportunities.
The Founder Effect
    The
founder effect
is the tendency of initial, successful occupants of a niche to have an exceptionally strong effect on succeeding generations. The effect holds when the rate of interbreeding among first settlers and their seed exceeds the rate of breeding with newcomers. 14
    One illustration of the founder effect concerns the Amish, who live in Central Pennsylvania, where I happen to reside. The Amish live in insular communities. They