EDGE: Examples?

MILLER: This revival of sexual selection in biology was of course promoted very strongly by people like George Williams, E.O. Wilson, an ingenious Israeli biologist Amotz Zahavi, and many theoreticians working alone in their offices writing down mathematical proofs showing that sexual selection could indeed work, just the way Darwin thought.

Some of the exciting new ideas coming out now are that many of the traits we're selecting when we choose a mate are not just arbitrary traits, they're not random, they're not meaningless, but they're actually powerful indicators of things that matter in reproduction—that a lot of beauty is really an indicator of health and fertility, and a lot of traits that are psychologically attractive to us, like kindness, warmth, creativity, intelligence, imagination, also are not random but actually are indicators of somebody's ability to get along in the world—not just physical world but the social world, and that in choosing a mate for these psychological qualities, we're insuring that we have a partner with whom we can have a constructive relationship, rear successful offspring, and to pass their better than average genes on to our children. What we're seeing here is in studying how people choose their mates, not just for physical appearance but for all these rich psychological traits, it's a wonderful confluence between evolutionary biology, personality theory, and evolutionary psychology. And that to me is very exciting.

One of the great surprises for David Buss, one of the leading evolutionary psychologists studying mate choice, was that when he did his wonderful study in the late '80s of sexual preferences in 37 cultures all around the world, giving questionnaires to 16,000 subjects that just span all sorts of cultures with all sorts of languages with different traditions and different histories, he found that in every culture, the top two most desired traits in a mate, for both sexes, were kindness and intelligence. It wasn't physical appearance, it wasn't money, it wasn't status, it was these psychological traits, and these are universally important. They're also the two traits that Darwin tried to explain about our species—why are we so nice to each other and why are we so smart? Relatively nice, compared to other primates. And that's fascinating, that two of the major traits that distinguish us from other primates are the same traits that we search for in mates—that are currently under the strongest sexual selection. My hypothesis is that they're not just under sexual selection now, but they have been for a very long time, perhaps hundreds of thousands of years, and the reason we're so smart and so relatively kind to each other is that our ancestors who were smarter than average and kinder than average attracted more mates and higher quality mates.

Another interesting question is about language. Language is a really tricky case because, as Steven Pinker has pointed out, language is extremely useful for many functions. You can tell your friends how you're going to hunt an animal and cooperate on tracking it down. Women can tell their friends where the best roots and berries and tubers are growing this season. Parents can tell their kids all sorts of useful information as they're growing up. Of course the principal way that people court each other is through language. Human courtship is largely through conversations. It would be foolish to say that sexual selection was the only force shaping language; clearly survival selection and many other forces were shaping it as well, but I would claim that some of the more mysterious aspects of language can be understood only by thinking about how language is used in courtship.

A project I'm very excited about at the moment is trying to understand why humans have such large vocabularies. The average human knows about a hundred thousand words by adulthood. That requires memorizing arbitrary patterns that relate sound to meaning. It requires memorizing ten words a day every day from age 18 months to age 18 years, and that's a fantastic feat of learning. There's nothing else like it that humans do. The funny thing about that vocabulary is how little of it we use in ordinary conversation. We get by in our day to day speech with just a few thousand words counting for 95% of all the words that we say.

There's are a tremendous number of words we've learned that are not used very often but that we bothered to memorize, that don't seem to be very useful in ordinary day to day life, but that we still sometimes use with each other—and those are the words that I want to explain—not the 5,000 most useful words but the 95,000 ornamental words. My prediction is, people mostly use them in courtship. They use them essentially to show off, they use them to show how bright they are, how good their learning ability is, how good their memories are for words. We know in the brain where these words are remembered, roughly in Werneke's area, in certain parts of the left hemisphere, we know that there's specialized brain machinery for learning these words; we know that vocabulary size is an extremely powerful indicator of intelligence—this is why vocabulary items are used in IQ tests; within a few minutes of conversing with somebody you use the vocabulary that they're producing as a pretty good indicator of how intelligent they are—so it's a extremely useful thing to use in mate choice. The hypothesis here is that vocabulary size itself has been strongly shaped by sexual selection, and that most of the words that we know have been learned not because they're useful for survival, but because they're useful for courtship.

Another mystery is why we enjoy music so much—and this is one of the questions that Nicholas Humphrey has asked in the EDGE forum. Music has such powerful emotional impact, and nobody has ever found a good survival function for it. The very first serious conference on the evolution of music only took place last year at a wonderful little town called Fiesole, Italy, in the hills overlooking Florence. It became abundantly clear to me at this conference that there were amazing parallels between human music and bird song, and whale song, and all the other complicated acoustic signals that animals send to each other-even gibbon song. The most musical apes are gibbons who do wonderful duets, long calls that they give to each other, especially to their sexual mates. Wherever you're looking in nature, if an animal is producing a complex acoustic signal it's almost certainly a courtship signal, it's almost certainly involved in sexual selection. We know this for bird song, we know it for whale song, and we know it for gibbon song.

Darwin thought the same should apply to human music, that human music was largely an outcome of courtship displays. That's a wonderful overlooked theory, and it's surprising that people have scrambled for a century, coming up with all kinds of silly hypotheses about music functioning to make people in a group feel closer to each other and to facilitate group cooperation, for example—that's a favorite idea. If you go to any nightclub in London or New York or Berlin or Tokyo you can see the proper context for understanding music's function. Although it's done in groups the point of it is individual display.

Music combines exactly the features that an evolutionary biologist would predict—for something that indicates an individual's creativity, motor control, self-confidence, and lots of other traits that are important in courtship. Music is a system of basic elements, notes, that are combined according to certain principals of rhythm, tonality, and we know that the basic principals of rhythm and tonality and melody are universal and cross cultures. Even though many of the musical styles are different. And that people can demonstrate their coordination and virtuosity, both as musicians and dancers, by using this system that has stereotyped basic units. The essential thing about rhythm is that you can see whether somebody is rhythmic or not, whether they're coordinated or not. If rhythm didn't exist it would be hard to tell whether somebody was keeping to a regular beat, and whether they could coordinate their body and their musical productions according to a regular beat.

To tell how good somebody is at something there have to be some rules, there have to be some regularities, but for them to demonstrate how creative they are, how innovative they are, they also have to be able to play around with those basic elements, and play around with those rules. Music also provides great scope for that—for melodic innovation, for improvisation, for producing innovative lyrics, for producing unusual timbres when you're singing, or playing an instrument. It's the perfect display, really, for sexual selection theorists. Art and language and many other display forms that we have follow some of the same rules—we combine basic elements that are stereotyped in ways that are innovative, and that's a recipe that you need to indicate your quality to a sexual prospect.