The Sexual Male, Part One: The Flight of the Spermatozoon

In the first of a series of in-depth reports on the science of male sexuality, we track a sperm cell and its delicate payload, the underrated y chromosome, on their fantastic voyage to make a man. You’ll never look at your balls the same way again.

In the time it takes to read this sentence, your testicles will have produced 5,000 sperm. By the end of this page, another 100,000. A billion more wait in reserve. They hope to be released inside a vagina, but if no woman is available, they will find a way out. Your brain will help by providing a fantasy in which the female doesn’t say no. Your brain is generous with these fantasies. You can’t walk down a runway of breeders like Fifth Avenue in Manhattan without judging every woman in an instant as doable or, in more polite terms, as a means to push your genes into the next generation. If you could have a quickie with every five or better without expending any effort besides catching up with her, and she would bear your child without asking you to stick around (with the exception of a few playdates; you’re not heartless) or pay for anything, how many kids would you create? Moulay Ismail the Bloodthirsty, ruler of Morocco from 1672 to 1727, is the official record holder, with at least 867. Because with as much grief as men get for our seemingly boundless sexual appetites, it’s not about getting off. We can do that on our own. At the most basic level it’s about ego: There can never be too many versions of you.

That biological truth drives the conveyor belt in your testicles. It also drives this article, the first of a series that will examine what scientists know about male sexuality. The sperm factory is a natural place to start because the tenacity of a single spermatozoon produced by your father’s factory is (along with his seduction skills) the reason you exist. A man’s sperm factory operates 24 hours a day, seven days a week, from about the third grade to as long as 48 hours after death. The genetic material packed into the head of the first sperm to penetrate an egg—the lone survivor in a sprint that resembles either the Boston Marathon or Death Race 2000—determines whether an infant will be born with a penis or without (with a few notable and fascinating exceptions).

The spermatozoon that created you, the quadrillions you will produce and those made by your sons constitute a brotherhood. Each contains a nearly identical Y chromosome, the trigger that makes the man. We will ride these sperm for the first part of our journey. Saddle up.