What is it about the cliché, Mr. Tall Dark and Handsome that rings true for some, but not all, women? What contributes to our desires and sexual attractions? Might they be simply picked up through culture, possibly biological or a mix of both? Many of the things that people find attractive in a potential partner can be linked to fertility and reproductive health. That's right -- some of the physical characteristics, even the scents, that turn you on may be an indicator of future amorous success.
Like olive oil, sperm also come in different grades of quality. Extra virgin olive oil, the priciest first press of unblemished olives, is just like sperm with less aneuploidy. In an average, healthy man, one to four percent of his sperm has aneuploidy, that is, sperm that has more or less of the usual number of 23 chromosomes. Besides affecting fertility, higher percentages of paternal aneuploidy have been linked to miscarriage, birth defects and congenital disorders like Down syndrome.
Like all of the hard work it takes to produce extra virgin olive oil, men's bodies spend a considerable amount of energy and time trying to make healthy sperm which is free of aneuploidy. That's why it's used as an important benchmark of sperm quality.
Most people have heard of folate or folic acid and its importance in preventing neural tube defects during pregnancy. But when it comes to men, the truth is, little is yet known about men's nutritional status and how that affects the quality of their sperm.
New research is now suggesting the possibility that one of the contributing factors to sperm quality is folate, an important nutrient found in leafy greens, like spinach, which is already known to promote reproductive health in women. Folate plays a critical role in the production of new cells. When you consider that men normally churn out new sperm cells at the incredible rate of around 100 million a day, you can see why folate is important. Sure enough, a recent study showed that men who consumed much more folate, through diet or supplements or a combination of both, had as much as 30% less aneuploidy.
Okay, but what does all this have to do with skin tone? Well, ultraviolet rays, specifically UVA, destroy folate. Skin tone is created by special cells that produce different types of melanin, such as eumelanin, which are naturally occurring pigments that absorb ultraviolet radiation and release it as heat, protecting the body from its harmful effects. The darker a man is, the more protection he has from ultraviolet rays and the less folate is destroyed. And possibly, the healthier his sperm. So if you're hoping to be a father, it can't hurt, eat your spinach.
Now, none of this means that culture, upbringing, sexual orientation and all kinds of other factors don't play a significant role in attraction. They do.
The reason not all men are dark-skinned has to do with a classic evolutionary compromise. Turns out that if all men were on the darker end of the skin tone spectrum, they would end up lacking vitamin D. Besides getting vitamin D through our diet, we normally need the help of sunlight to produce adequate amounts. Having enough vitamin D also keeps us from getting rickets and other possible immune related disorders.
If you have dark skin today and live in places that don't get enough sun, such as the northeastern United States, your folate may be protected, but the lack of vitamin D can affect your health. It may even put you at an increased risk for certain types of cancers.
Of course attraction, especially across the sexual orientation landscape, is much more complicated than just looking for partners with ample sperm. Sex plays a much bigger role than just reproduction, as almost everyone can attest, and there an incomprehensible amount of processes go into selecting a partner and maintaining a relationship. Sometimes we are aware of them and other times these processes are occurring subtlety, seemingly beyond our control.
I've spent the last few years peeking into a bedroom or two (only upon invitation) and working in the lab to study and write about how sex works. We may never know for certain why we find ourselves attracted to one specific person and not another.
But it's the incredible fascination of trying to understand our unique preferences, by exploring the cultural, biological and historical facets involved in and surrounding our own sexuality, that in the end can make sex all the more pleasurable.
Sharon Moalem is the author of the new book "How Sex Works: Why We Look, Smell, Taste, Feel, and Act the Way We Do"