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Biology 103
2003 Second Paper
On Serendip

Sexual Selection: Fact or Fiction

Natalya Krimgold

Darwin's theory of sexual selection is an intriguing one because it offers an explanation of human striving and cultural value systems. The theory is that humans who are more sexually desirable will have more offspring and thus their traits will be passed on to future generations to a greater extent than those of less sexually desirable humans. As opposed to Darwin's other theory, natural selection, those who are the best adapted to their environment will be more likely to pass on their genes, or, "survival of the fittest", you might call sexual selection "survival of the sexiest." The theory is intended to in part explain why, when humans diverged from other primates, the human brain tripled in size in just two million years. At first glance, this theory also seems to explain much of the motivation behind human culture and achievement. Upon closer inspection, there are some fairly conspicuous problems with it, especially when it is extended to describe not only human evolution in the distant past but it the present, but it may still be the most plausible explanation available to explain why humans mental capacities have expanded so far beyond those of our primate relatives.

It makes complete sense that we would be biologically driven to prove our sexiness. At the most basic level, this could explain the plenitude and popularity of fashion magazines for young women and the emphasis on being good at sports in school for both genders. Beyond this, it could also explain why men and women are driven to succeed at their various careers, or to be perceived to be successful, smart, witty, fun-loving, good-looking, responsible, or any of a number of things that human aspire to be which are also sexually attractive. The drive for achievement could be rooted in their biology - and their desire to be considered sexually desirable.

What is interesting is that while it seems logical that the desire to succeed is rooted in the desire to appear sexually desirable, (and by that standard, many people are trying very hard to be sexually desirable), in this day and age, sexual desirability bares little or no direct correlation with the number of offspring one produces. In fact extremely sexually desirable people, supermodels, billionaires, sports stars, and affluent people in general, tend to have fewer children than those who are less sexually desirable by this definition. Even so, many of us are highly motivated to prove our sexual desirability, but the purpose of doing so, if it ever existed, seems to have been lost or distorted.

Was it ever really true that the more sexually desirable people had more offspring, or is this theory only speculation? According to Geoffrey A. Miller, a senior research fellow and University College London, anthropological data show that in our hunter/gatherer days good hunters had more extra-pair copulations than poor hunters, but that is hardly concrete evidence that good hunters actually produced more children than poor hunters (4).

Miller rejects both the rapacious male/helpless female and the choosy female/displaying male models of sexual selection. (Studies done with primates suggest that male and female hominids exercised mate choice and followed a pattern of serial monogamy, and that rapists would have been ostracized or killed.) Instead he believes that over the course of evolution, both sexes have had substantial choice in sexual partners, and even in the case of arranged marriages, the parents have exercised choice of sexual partner for their children based on certain desirability standards.

If the theory does hold, and, in the past, at least, those who were more sexually desirable did indeed have more offspring, that would imply that, over the course of human history, humans generations were getting sexier and sexier, meaning that whatever traits were valued in terms of sexual selection were becoming magnified in the human population over time.

Some of the diverse traits that Miller suggests as possible factors in sexual selection are art, morality, language, and creativity. In the case of art, his argument is that it acts as an extended phenotype, basically demonstrating the biological fitness of the creator. The argument for morality is based on modern (unsubstantiated) sexual abhorrence of selfishness, lying, and cheating, and a study by David Buss (1989) which found kindness to be the most desired trait in a mate across 37 cultures (4). In addition, traits like conspicuous magnanimity are good fitness indicators. The language argument is predicated on the belief that there are more words in most languages than are necessary for survival so they must serve some "self-advertisement" function. In addition, he claims that today, vocabulary is more influential than any other mental trait in mate choice. In terms of creativity, with the assumption that courtship entails a great deal of conversation, Miller concludes that there would be plenty of time before the probable time of conception for either lover to decide to dump the other on the basis of speaking, listening, thinking, remembering, storytelling or joke-telling ability. (He cites Cyrano de Bergerac as an example of these sexually desirable abilities at work.) In addition, he theorizes that early humans, as humans today, would become bored with predictable mate, so unpredictability, a form of creativity, was probably a sexually selected trait. (4)

The problem with this theory is that it is largely speculative. You could claim sexual selectivity for any trait that humans today possess, and I see no reason why positive traits like creativity and morality should come before negative ones like unimaginativeness and immorality, which are also in abundant supply today. Sometimes the positive and negative are even inextricably linked.

Creativity, which Miller credits partially for the rapid evolution of the human brain, has also been linked with mental illness and attention deficit disorder (Evolution, Creativity, and ADD ). Thus creativity can often be detrimental to the individual who has it or the society in which they live, but on other occasions, it can lead people to create great inventions and works of art. Because of the potential detrimental effects of creativity, it would not be useful for everyone in a society to be extremely creative, because this would probably mean that a large proportion of people would also be mentally ill or have ADD, and pandemonium would ensue (2). Conversely if a small portion of the population possesses these traits, the detrimental effects remain manageable, and the rewards are still great. In this case, the theory of sexual selection might not be applicable, because it would not be beneficial to the species to produce such unstable elements in greater and greater numbers.
Furthermore, who is to say that everyone is attracted to the same characteristics. Some people may value kindness in a mate, but others may consciously or unconsciously like to be treated cruelly. In addition, I see no reason why people who are more sexually desirable would have more offspring, even in earlier stages of evolution. Sure they might have a greater choice of potential mates, but does that mean they would necessarily have children more often than ugly, unsuccessful cavemen and women did with each other? After all, just because they are more sexually desirable does not necessarily mean they enjoy sex more or have more children, and just because they have more choices in terms of sexual partners does not mean that undesirables were left without anyone with whom to copulate.

In more general terms, I see no reason to believe that the human race was or is becoming more creative, ethical, or verbal, with each passing generation. Instead, it seems much more logical that as a species, we maintain a stable proportion of people with varying creative and verbal capacities, and that ethics are only marginally, if at all, genetic. The one instance in which this theory makes any sense at all is over the course of the two million years when human brain size tripled. However, even then, natural selection, not sexual selection, or perhaps a totally different force was responsible for this dramatic change. Maybe certain traits were considered unacceptable culturally and so no one was allowed to mate with people baring these characteristics, even if they were sexually desirable - one could call this cultural selection.

On the other hand, what other way is there to explain the importance most people attach to being sexually desirable: beautiful, smart, sociable - successful. What other biological reason is there for us to be so driven not merely to survive, but to succeed, to prove ourselves, and why else would we have so much of our emotional well-being wrapped up in whether we succeed or not? According to the theory of sexual selection we care about success because success makes us sexy, and reproduction is the biological purpose of life. Still, it is clear that if sexual selection ever did function, it has become completely perverted (no pun intended) now; the most successful people do not have the most offspring. It is difficult to judge whether or not sexual selection functioned in the distant past because there is only patchy data to support or give evidence against it.

The other problem I have with this theory is that it is too deterministic. It attributes too much to genetics and not to human striving. Vocabulary, for example, is acquired, not inherited. If it is highly heritable, as Miller suggests, this is probably because children generally learn to speak from their parents, not necessarily because they share a similar language learning ability. Ethics are even more difficult to attribute to genes. Decisions, in general, ethical ones should be no exception, tend to be based on past experience not DNA.

The perspective that our genes are the only thing attracting us to each other is fundamentally depressing. What is the point of human striving if everything is predetermined by our genes? Or is the only point of all of our striving to prove to society and potential mates the genetic capability we had all along: is success an extended phenotype? The truth may be that even we don't know the true extent of our genetic capability until we try to test it out in the real world. Still, true ability always remains ambiguous because there can always be barriers to success even if you do have the genetic capability for it. Certainly one can't achieve things without a certain innate ability. Perhaps we all strive to achieve in order to reach our full genetic potential so that others will know the full extent of our genetic desirability. We are frustrated when we fail because it either means we aren't living up to our potential or we don't have the potential at all. Luckily, we can give ourselves the benefit of the doubt because as of yet, there is no way to measure to absolutely measure "potential", or our genetic make-up. Luckily, as well, if we don't have certain sexually desirable traits, like physical attractiveness or intelligence, we can always have others like kindness and magnanimity.

Humans are relatively more creative, verbal, artistic and ethical (by our standards) than other primates and the theory of sexual selection does provide a plausible explanation for this. Early humans probably did select mates who had relatively greater capacities in these areas. This would explain why brain size increased so rapidly. However, the theory does not necessarily extend to recorded history. Even if this theory was once true, it does not appear to hold true anymore, because those who we consider the most successful and desirable are not producing the greatest number of offspring, and so, the traits that are being selected for future generations may be entirely different. Ironically, we may be spending our lives trying to prove we have traits which evolution is actually selecting against.


1) Creativity, Evolution and Mental Illnesses

2) Evolution, Creativity, and ADD

3) Sexual Selection and the Mind: A Talk with Geoffrey Miller

4) The Mating Mind: How Sexual Choice Shaped the Evolution of Human Nature

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