Death… It's A Living

In the previous post, I wrote about how the female of the species is the choosier of the two sexes. The reason for this is simple: She, unlike her male counterpart, can becomes pregnant. Because pregnancy requires a significant investment of physical and social resources, females should be careful with their mating opportunities. Males do not require such care when choosing a partner because they do not produce and release a limited number of gametes in their lifetimes, nor do they become pregnant.

We see this fact of nature played out when modern humans seek out dating partners. In a now classic set of behavioral study that began in the late 1970s, a group of young, attractive adults were trained to proposition unsuspecting undergraduates on an American college campus. People my age might even be familiar with this study without knowing it, as the script found its way into a top-10 dance track in the 90s. The study confederate approached a potential partner and asked,

“Um. I’ve seen you around. I find you very attractive. Would you go to bed with me?”

The research question asked whether the men and women propositioned would have different responses. To absolutely no one’s surprise, they did, and it wasn’t close. In fact, nearly all of the men approached by an attractive female said ‘yes’, whereas none of the women agreed to sleep with a strange man.

Of course, this does not mean that the female of the species is completely unavailable for sex, but it does mean she is careful. She has the biological imperative to be choosey. As such, she must know what she is looking for. And although some of what she is looking for is fairly predictable (more on that later), much of it is far more idiosyncratic and must be viewed through the lens of individual differences.

The Power of Female Choice

Before writing much more, I confess that I often find the study of individual differences frustrating. I became a behavioral scientist so that I could ultimately learn why people do the things they do. As a result, I gravitated toward social developmental psychology because the theories that comprise this subfield attempt to answer various aspects of that broader question. Of course, no theory (at least no theory in psychology) always predicts the behavior of individuals with 100% accuracy. This is not because people have free will and can choose to become whatever they want to be (though wouldn’t that be nice to believe?); rather, it is because there is a randomness that exists in all closed systems, and not all outcomes can always be foreseen. Specifically, evolution has ensured a degree of randomness across our genetic codes. This randomness presents as individual differences, which—from a psychological perspective—often means personality. Parents who are conscientious are more likely to have children who are conscientious, but there is no guarantee. In other words, I find the study of individual difference frustrating because it feels like an additional, unexplainable alchemy is being added on to an otherwise predictable science of behavior. We know a lot about why people do the things they do in general, but we will never understand—at least not in my lifetime—why each individual behaves in specific ways in each environment.

To come back to where I began in the previous post, individual differences matter when it comes to choosing who or what is most attractive. This is one of the most basic (and oldest) ideas of Darwinism. In fact, for Darwin, it was the individual differences in attractiveness preferences present in all mating species that best explain species differentiation over deep time. In his excellent book The Evolution of Beauty, ornithologist Richard Prum gives added evidence and revives Darwin’s (likely accidental) feminism. Prum provides a convincing case that although Darwin’s Big Idea forever changed all of the life sciences, one of his most important ideas was mostly lost to history because it was not in keeping with the (even more) patriarchal times of Victorian England. In short, Prum argues that Darwin believed it was not just individual differences but individual differences in female choice that leads to successful mating and species differentiation.

Both Darwin and Prum studied birds, so let’s use birds as the best example. Even non-birders like me know that many species of bird (though not all) show extreme forms of sexual dimorphism; that is, the males looks radically different from the females. In all of those cases, the males compete with each other to be noticed by the females. In many cases, they work incredibly hard to win even the opportunity to approach a female. During mating displays, the male performs some action (depending on the species) to convince the female he is worth her time. Some males dance, some display their full plumage, some sing, some collect shiny stones—there are probably hundreds if not thousands of uncatalogued mating displays across the tens of thousands of bird species.

Following his display, the male waits.

The female may find herself swept off her talons by her suitor’s presentation. Or she might fly away. The male’s chance to mate may have to wait until next season… if it ever comes. His only chance to ensure his genetic survival is due to a not insignificant amount of random chance: Do I have what this female wants? In this way, Prum—by way of Darwin—argues that it is females (across all species) that determine whose genes will survive and whose will become evolutionary dead ends.

History failed to emphasize the power of female choice. This is unsurprising considering that even 70 years after On the Origin of Species, the Catholic Church’s official position on the parity between men and women was that it was “against nature”. Many might still argue this is the church’s official position, given that no woman can serve in the roles reserved for men. Thus, female choice was reduced and considered as a fickle whim. Today, we should recognize that those fickle whims are why all life is as it is today.

Specifically, female choice influenced male appearance by giving it extreme variability across the species. Importantly, the same is not true of female appearance. Again, only thinking of birds, many females are relatively drab and boring in appearance. Female mallards and peahens certainly cannot compete with their male counterparts in terms of raw beauty. Female birds don’t need physical beauty to be sexy to males, they simply need to be fertile. If sexual attraction is a cue toward a mating partner, then there should be only one thing that drives male attraction: signs of fertility. Thus, there should be less variation in female appearance. Females who fit a prototype should be preferred, and the fickle whims of what their males want to see in an ideal partner are of little importance to the future of the species.

The Whims of Humans

Although humans are slightly more complicated when it comes to mating displays (more on this in a bit), female choice has nevertheless played a significant role in shaping human appearance. As with many species of birds, there is greater variability in male appearance than female appearance. Although this seems like a subjective statement, it is supported by work in forensic anthropology. Scientists working in this field have examined the skulls of men and women over the last 400 years and have found that variability in female skulls is reducing; that is, over time, women have started to look more and more like other women. The same is not true of male skulls: There continues to this day to be a significant amount of variability in male (human) facial appearance. Another way of saying the same thing is that there are far more extremely unattractive men than there are extremely unattractive women. This fact should not be surprising if we remember that men are attracted to females who display signs of fertility: A certain waist-to-hip ratio is important, but so are specific facial cues brought on by puberty. Regardless of culture, men find young women with full lips, clear skin, and high cheekbones to be attractive. These traits are highly correlated with a high degree of estrogen, a marker of female fertility. Thus, the females who have the power to choose their mates are the most fertile, and the most fertile females all look a certain way. Male attractiveness, on the other hand, is driven by the fickle whims of the individual female. Thus, over time, male faces have retained their variability.

Incidentally, we gain more circumstantial evidence of this finding when we look at Renaissance art. Look at the faces of the men and women painted by the Italian and Dutch masters. Note how the men tend to look like the men of today, whereas the women tend to look less attractive than real 21^st women (or those painted 300 year later). Female faces are getting more average (and therefore more attractive!) though the forces of evolution. Men, not so much.

To recap thus far, human beauty and our preferences for beauty are intimately related to our ability to detect specific genetic survival cues from the environment as well as our willingness/ability to invest resources in any potential offspring that should result from interactions with that beauty. Perhaps the most important but mysterious driving force in all of this is female choice. As I suggested above, however, much of female preference for the attractiveness of potential mates is predictable. That’s where I’ll start in an upcoming post.

-The Plague Doctor