Why is Sex Fun? summary

Although men’s and women’s dedication to their children will differ immensely across relationships and contexts, most fathers will at least play some role in a child’s life. But funnily enough, when we look at human fertilization, it’s not immediately obvious why.

One main factor underpinning the commitment of each parent to a child is the investment in the fertilized embryo or egg. Just as we would hesitate to quit an ongoing project that we put a lot of effort into, a female producing an egg is normally more committed than the male that supplied the sperm.

Another way in which our sexual practices support monogamy is through our oddly-timed attempts at fertilization.

Most animals have sex only when fertilization is likely. But we are different. Humans have sex regardless of where the female is in her menstrual cycle, and even during pregnancy and menopause, when fertilization is impossible. Why? Because human males have no natural way to know when their partner is most likely to be fertilized.

Considering that they mostly distance themselves from the mothers of their offspring and the offspring themselves, most male mammals aren’t particularly useful, aside from injecting sperm. They leave after they copulate, shirking any fatherly duties thereafter.

But human males are different: they often stay with their mate and offspring after sex.

Not all species display expected male and female roles. For instance, male seahorses, not females, are the ones that get pregnant. As we’ve seen, there are surprising ways in which our own sexuality and our bodies have evolved over time, and lactation is a prime example.

You may not know that lactation can occur in most mammals independently of pregnancy. In fact, repeated mechanical stimulation of the nipple is enough for milk to begin secreting. It’s also been found that, starting from one month prior to bringing a child home, adoptive mothers can use breast pumps every few hours in order to simulate suckling – and actually produce milk.

Another of nature’s curious creations is menopause – the ceasing of a woman's egg supply which leads to sterility.

Human menopause doesn’t fit into the animal world. If natural selection is about promoting the genes of a species to increase its chances of producing descendants, then menopause is a paradox, especially since most animals are fertile until they die, including human males.

Let’s take a look at another trick we’ve developed through evolution: body signals. These are instantly identifiable cues that tell others about our biological attributes, such as our sex and age, as well as our intentions, like aggression.

Indeed, all animals rely on different ways of communicating various information, like auditory or visible signals. In the case of birds, they use song to attract mates, or plumage to communicate their sex.