Selecting for Sex

My first kiss took place beneath a lunchroom table. The object of my affection was Whit Winfrey, a beautiful, blonde boy with striking blue eyes and tan arms adorned with feather-soft, white hairs. I lured him under the table to show off to my girlfriends, who had the audacity to doubt my ability to snag a kiss amidst the glaring gaze of the lunchroom monitor.

I succeeded, Whit was baffled, and I smugly returned to my sandwich as my girlfriends looked on in awe. Such is love among fifth graders.

It amazes me that I can remember such detail about Whit’s beauty, especially since many of my boyfriends have faded into the dark recesses of my memory. Whit was the first in a long line of fair-haired boys (with a few brunettes sprinkled in for variety) and even today, I’m a sucker for the blondes. But why? Why do we prefer certain physical traits over others?

Close your eyes and think about what turns you on (please keep your hands where I can see them). Are you a breast man or is it long legs that float your boat. Ladies, do you like a hairy chest or prefer a baby-smooth landscape? We all have certain physical traits that appeal to us more than others. What you may not have considered during your lustful meditations is the role attraction plays in evolution.

There are three primary elements of evolution. The first is mutation, commonly referred to as “descent with modification.” Without subtle changes in the genetic code, the second element, natural selection, would have nothing to work on. A fixed and unchanging organism wouldn’t last long in the dynamic environment of earth, and it’s the chance mutations that happen to confer an advantage that enables them to take hold in a population.

The third element is sex, or more specifically, sexual selection. Sex is nothing new; it’s been around for about a billion years.

Prior to the advent of sex, organisms reproduced asexually and many still do today: bacteria, protists, some plants and fungi, and even some animals. There are many ways to do it (or should I say, not do it): fission, budding, and spore formation, to name a few. There’s also parthenogenesis, in which the embryo develops without fertilization. If you were an aphid, a water flea, a hammerhead shark, or a komodo dragon, you’d be able to fly solo when it came to procreating. Think of all you’d be missing...

The development of sex was a boon for evolution. It is believed the recombination that occurs when organisms reproduce sexually, and therefore exchange genetic material, may purge bad mutations from their DNA. Recombination also provides a buffer against harmful mutations, since you have a fifty-fifty chance of getting a “normal” copy of the gene from one of your parents (which is why inbreeding is not such a good idea). Sex may also help fight disease by promoting the evolution of new genetic defenses. So to state the obvious: sex is good.

But a big part of sex comes down to choosing a mate. Here’s where things get really interesting.

How and why we choose whom we choose is based on what we find attractive in a mate. For the most part, it’s all about “fitness.” Fitness, in the biological sense, refers to an organism’s ability to leave behind offspring. Fitter individuals, be they moose or mollusks, will leave behind more moose or mollusks than their less fit counterparts and, in many cases, it’s the females who will do the choosing. As you can imagine, fitness has a broad range of expression, depending upon which species you belong to.

Take that moose, for instance. A female moose is wise to choose a male who’s muscular (and therefore can outrun predators) and one who sports a large rack (bet you never thought you’d hear that in reference to a male). That large rack will enable him to out-compete rival males as they vie for females.

But here’s the conundrum: the wild and whacky world of sexual selection appears in many ways to conflict with the basic premise of evolution. Natural selection is supposed to favor those who are better adapted to survive, yet many physical attributes that crop up as the result of sexual selection actually reduce chances of survival by encumbering their owner with extraneous or physiologically expensive accoutrements (the peacock’s tail is the typical example) .

A moose may develop an enormous rack, which gives him an edge in combat displays, but it’s also pretty darn heavy, making it more difficult to outrun a predator. Same with that peacock. He may strut around and display his tail to lure a prospective hen, but try evading a coyote while dragging that feathery aphrodisiac. My money’s on the coyote.

Natural selection has come to terms with this predicament. If an individual can sport such elaborate ornamentation (be it a giant rack or a monstrous set of tail feathers) and still survive and reproduce successfully, that individual passes the ultimate fitness test and will usually go on to leave more offspring.

As for humans, fitness is still defined by physical traits that represent mating potential, whether it be a beefy, masculine male or a voluptuous, fertile female. But we are also cultural beings, and today, culture dictates much of what we consider desirable in a mate.

And among us westerners, seems all you need is a flashy car or enormous breasts and you’re in like Flynn.

Happy hunting!

Since you now understand the fundamentals of selection, next week we'll delve further into the evolution of sex itself. Stay tuned and have a great week.








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