Sex fascinates us; it makes or breaks marriages, ruins political careers, and is the backbone of the internet entertainment industry. And yet it is something hidden, as if we were ashamed at its fascination. In my work, I always ask people who come to see me what they do for fun. Of thousands of replies to this question over the years, I have had exactly one person list sex. Surely there are a lot more people than that who find sex something to do for fun. And besides being fun, sex is interesting. It is one of those universal activities that you can never learn everything about or participate in all its variants. There are many enthusiastic guides about how to have sex (the best of them is _The Guide to Getting It On!_), but if you are more interested in why we have sex and why people do the sexual things they do (including yourself), you are bound to gain insight from _How Sex Works: Why We Look, Smell, Taste, Feel, and Act the Way We Do_ (Harper) by Dr. Sharon Moalem. The author is a neurogeneticist, evolutionary biologist, and physiologist, but he is used to writing for a popular audience, and this book gives lots of facts, from trivial to essential, about a topic that is always interesting. If you had a good sex ed. class (bet you didn't), many of the subjects in Moalem's book may be familiar, but there is new research in many aspects of sex and new ways of understanding its evolutionary importance, and Moalem has incorporated much of it in a readable and amusing fashion.
Sex is pretty costly, and that isn't just because of the price of dinner and a movie. It takes energy, and putting two half-cells together to make a new starter cell for a new individual is enormously complicated and can go wrong in countless ways. On the plus side, it jumbles the genes every generation, which not only makes it hard for parasites and viruses to ride along, but also allows variation in every new individual, enabling evolution to make its changes. Jumbling the genes may be something we are programmed to do. Moalem reviews studies that show how olfactory and visual cues may help us have the best chance of sending good DNA to our progeny. There are also studies to show how sex works internally. The more attracted a woman was to her partner, for instance, the easier and more intense were her orgasms; good orgasms produce more of the hormone oxytocin, which is thought to increase bonding. It's a nice positive feedback system, and indicates how essential good sex is to a good relationship. It would be a sorry sex book that didn't have pages on penis size. Guys, it's time to relax: although only 55% of you are happy with the size of your penis, 85% of women were quite satisfied with their partner's penis size (and though Moalem doesn't say so, some of the remaining 15% must have had dissatisfaction with too big, not too small). But size does matter: condoms have to fit, especially non-latex condoms, which don't have the stretch of the typical rubber. Moalem describes working for an agency in Thailand where western visitors to brothels reported that condoms were breaking. The problem was that local Thai condoms were smaller than those fit for men from the West.
There are controversies even in science about the dimly-lit biology of coitus. Moalem agrees (despite some studies to the contrary) that there is a physiological G spot. The ancient Greeks and plenty of other observers have been telling us there is such a thing as female ejaculation, and Moalem cites modern experts who say it isn't just a myth, though perhaps not every woman can do it and no woman should feel she is missing something without it. Focusing in one chapter on homosexuality, he points out that it seems to be programmed into the behavior of literally hundreds of species, part of a bonding mechanism between social animals. There is research that in at least some cases in humans, there is a gene that directs women to like men, and thus have more children; the same gene in men can cause them to like men. It's not all that simple; there are studies to show that a baby's fetal environment might play a role, and then of course there's all that post-birth nurture stuff. Moalem is interested in how technology is helping us overcome medical problems of sexuality, but also mentions "teledildonics" which is sexual remote interaction through the internet. There is little moralizing here. Connected to his review of male circumcision (which might have originated as a health practice but certainly took on a life as its own, including wrongly being thought to reduce masturbation), Moalem is strongly condemnatory of female circumcision. That's not the typical tone of his book, though, which in many chapters is a jaunty review of the most modern research on an old, old topic. Improved understanding can't hurt; one in five American high school girls, for instance, has no idea how HIV is transmitted. Moalem says that sex is one of evolution's greatest gifts; but so, too, is our intelligence to understand things scientifically. His book is an invitation to apply that intelligence in order to understand sex better, and what is strongly linked, to enjoy it more.