I’m not the first one to wonder why in humans, it’s often the females who adorn themselves. It’s not natural and you need to look no further than newly discovered Eresus hermani

to see yet another example of this.  Which one do you think is the female?

You guessed it. The one on the left. According to biologist Paulina Mena “Evolutionarily speaking, sexual selection has to do with investment in reproduction. The mode in nature is that females invest more in making gametes and in many cases in parental care than males. This means that females maximize their reproductive success by being choosy. This is what leads to the elaborate adornments, bird songs, dances, etc. in males. They are trying to be picked.”

Of course, as my anthropologist/sociologist friends point out, not all human cultures put an emphasis on female adornment. In some cultures, males and females are equally adorned or not and in others, the men are the fancy ones.  Jeff Bass points out that “There is a general observation that there tends to be less gender equality (or more female dis-empowerment) in societies based on intensive agriculture.” This possibly comes as women are less central to economic production, and is less of a factor in industrialized countries where there’s plenty of work for women to do. In this case, adornment is less important.

When males and females look different, it’s called sexual dimorphism. (Sexual dichromatism is the term for different coloration between males and females.) As far as humans go, we don’t have exaggerated sexual dimorphism. Some studies have suggested that when males and females look similar to each other, there is less fighting and competition among males. Is grooming oneself, trying to look different, encouraging competition? If we were a gender neutral society, would we be more peaceful?

Ever since Darwin brought it up in 1871, there’s been debate on WHY certain mates are chosen over others. Sometimes, it depends on parental involvement. If the female invests more, she’s the picky one. If males invest more (as in seahorses), it’s the male who is picky. Evolutionary biologist Paulina Mena says, “Biologically speaking, it’s not so clear-cut where humans stand in this spectrum. We see females adorning themselves but the fact that males don’t wear makeup doesn’t mean they aren’t trying to get females to choose them by showing something off. They just do it in a different way. Working out to have a very athletic body could be considered the equivalent. For example it has been proposed that even intelligence and artistic expressions like music may have evolved as a way to impress females and be chosen as mates. This offends some people because they don’t want to think that cultural expressions may have its origin in sexual selection. But then again, the idea that females are driving evolution through being choosy was also something that upset people until kind of recently. They had a hard time accepting that.”

Like many animals without distinctive dimorphism, white storks are monogamous–for a while.

Monogamy is the primary type of pair bond for humans, and this is prevalent across societies. When looking back at our ape ancestors, monogamy is more prevalent when the males and females have less physical differences. To quote: in primates, minimal levels of sexual dimorphism in body weight and canine size are generally associated with monogamy and low rates of male antagonistic competition (e.g., gibbons; Harcourt, 1981) Gorillas on the other hand, where males are twice as big as females, are not monogamous.

Smaller testicles related to body size is also correlated with monogamous species.

There’s been speculation on the driving factor behind some of today’s weirder cosmetic surgery trends. One theory is that the participants are trying to enhance sexual dimorphism and have taken it to the extreme. It could follow then, that those who take their procedures seriously would be more antagonistic and less faithful.

As an author, I sometimes have to make a choice for my characters: settle down or be libertine. Most readers of novels do not like unfaithfulness. The idea of romance especially is to successfully pair bond. I will make sure to avoid having any heroes with big balls or surgery and take it from there.

For more discussion, go here.