Under the microscope, the sperm would have looked perfectly normal by any modern standard. They had a nicely shaped head and long tail; they swam normally. And yet, as the Japanese reproductive biologist Masahito Ikawa had discovered at his lab in Osaka in 2003, this particular sperm could not fertilize an egg. It looked healthy. Any fertility clinic would have pronounced it good to go. But this sperm was broken.

For Ikawa, this discovery sparked a career-long obsession. Suddenly, he was dreaming of testing every sperm gene imaginable. He saw his research as having the potential to completely recast how sperm is viewed.

There is a pervasive idea out there about sperm: That the best of them are fast and powerful, the epitome of masculinity boiled down to a single cell. The strongest swimmer gets the girl. Scientifically speaking, though, that isn’t quite how it works. And this misconception has cost men a basic understanding of their own health. While female fertility has been a subject of intensive research for decades, male fertility is often treated as an afterthought.

Consider, for example, that most men seeking fertility treatment are first seen by doctors trained to treat women. There is no US body that routinely collects information about male reproductive health. There are just 406 urologists focused on male infertility in the entire US, according to a recent survey by the American Urological Association. “We don’t think of men as reproductive beings,” says Lisa Campo-Engelstein, the chair of the department of bioethics and health humanities at the University of Texas Medical Branch. “We conflate reproduction with women.”

But that misconception is finally starting to change. A worldwide decline in birth rates, reports of falling sperm counts, advances in technology, and a commercial boom in men’s health have all converged to drive a new interest in understanding how sperm actually works. Scientists around the world are now studying in detail everything from how sperm move to how they burn fuel. Some are even trying to grow them from stem cells. The work is urgent: Not only could it help the roughly one in six people worldwide who struggle to conceive, but it could also unlock an overlooked and poorly understood signal for overall men’s health.

In an orderly research lab on the lush suburban scientific campus of the University of Osaka, Ikawa has been deciphering the many mysteries of sperm for over 35 years, long before Silicon Valley start-ups were hosting sperm races or Elon Musk was giving away his own spunk in a one-man effort to stop population decline. Ikawa’s approach is simple and systematic: One by one, he is working to create model mice that lack each of the 1,200 or so genes thought to be key for sperm production, and then observing what happens when that gene is deleted. Twenty years ago, for example, he and colleagues discovered the critical role of IZUMO1, a gene that encodes a protein on sperm’s surface that’s essential in order to fuse with an egg. (It’s named for a Japanese shrine dedicated to marriage.) The mice missing this gene had normal-looking and behaving sperm, but were infertile.

Ikawa’s mice helped to challenge the basic assumption that a normal-looking sperm is a working one. And that assumption is nearly as old as the discovery of sperm itself. After Antonie van Leeuwenhoek first saw sperm under a microscope in the 1670s, many scientists became convinced each one contained a fully formed miniature human, the female egg merely a vessel. Even after that theory was debunked, for a long time many scientists assumed that sperm work the way we learned in high school sex ed: Legions of sperm race to the finish line, the strongest and fastest winning the prize. By the 1980s, researchers began undermining this idea. Sperm, for example, actually have a relatively modest forward propulsion, and they stick to an egg thanks to the adhesive properties of both sperm and egg. The feminist anthropologist Emily Martin refers to the myth of the virile sperm as a “scientific fairytale,” likening our ideas of sperm and egg to the same sort of gender dynamics you might expect in a classic rom-com.