Nathan Lents on the Evolutionary Lessons of Sex and Gender Diversity

Nathan Lents, a professor of biology at John Jay College of Criminal Justice, has spent years studying genome evolution, tracing how the DNA of humans, Neanderthals, and apes has changed over time. But alongside this research, he has also devoted nearly 15 years to teaching a course on the biology of sex and gender. Those classroom discussions accumulated into a wealth of examples showing how animals in the wild defy neat binaries of male and female, masculine and feminine. His new book, The Sexual Evolution: How 500 Million Years of Sex, Gender, and Mating Shape Modern Relationships, takes these lessons beyond the classroom. In it, he argues that diversity is not an exception in the animal kingdom but a rule, and that accepting this truth reshapes both biology and culture.

Nature Doesn’t Stick to Boxes

One of the first points Lents makes in his interview with Scientific American is that sexual and gender variation is not only widespread but natural. “What I show in the book,” he explains, “is that, especially with behaviors, there’s actually a variety within both of those [‘masculine’ and ‘feminine’], and that variety tends to overlap quite a bit.” In other words, nature doesn’t stick to strict boxes. Behaviors often cross boundaries, undermining the idea of “male” and “female” roles as clearly defined opposites.

The Binary Is the Real Problem

That leads to a second insight: the real problem is the binary itself. “The binary is really the problem, that these strict categories are not really upheld,” Lents says. He emphasizes that biology shows us continuums rather than neat divides, and when scientists force observations into categories that don’t reflect reality, they end up distorting the picture. Recognizing variation for what it is doesn’t just challenge stereotypes; it sharpens science.

Hidden Variations Can Save a Species

Perhaps the most striking example of this comes from a case study in crickets. A parasitic fly once devastated a population of singing males, leading to the rise of silent males who survived by avoiding detection. As Lents recounts: “Silent males always existed in crickets. … standing variation means you can adapt much, much quicker because you don’t have to wait around for a mutation.” That hidden variation became a lifeline, showing how traits dismissed as unusual can suddenly prove essential.

There’s More Than One Way to Be Male or Female

This connects with another theme in his work: there’s never just one “right” way to be male or female. “There’s not just one type of male out there; there’s not just one type of female,” he explains. Different strategies, even unusual ones, can succeed simply because they diverge from the norm. What looks odd in one context may be precisely what helps individuals or populations survive in another.

Scientific Bias Has Long Overlooked the Unusual

Yet history shows that scientists have often ignored such strategies. The silent male crickets, known since the 1970s, were once dismissed as “defective.” But, as Lents points out, if these traits were truly maladaptive, “natural selection would’ve eliminated them, but they haven’t.” Instead, they persisted, waiting for the moment when their difference became an advantage. The story is a reminder that bias, assuming one form of behavior is “better” or “normal,” has blinded researchers to valuable insights.

Culture Resists Change, Even When Science Pushes It

Finally, Lents acknowledges that these discoveries are not just about biology; they challenge deeply held cultural norms. “This area of sex and gender … it’s so tied up with gender stereotypes and a social order that we’ve constructed for ourselves that we all [feel] very committed to,” he reflects. That social resistance, he admits, means his arguments won’t land easily with everyone. But he hopes that by presenting the evidence with honesty, he can open minds: “That’s the only way … we’ll get to the truth.”

Lents’s interview shows how science often advances by looking again at what we’ve dismissed. The variety of sex and gender strategies in nature isn’t a side note: it’s central to survival, evolution, and resilience. In shining a light on that diversity, he not only broadens biology but also asks us to reconsider the human stories we tell about identity and belonging.