When it comes to biological and medical research, women's bodies have long been overlooked. Researcher and author Cat Bohannon says there's a "male norm" in science that prioritizes male bodies over female bodies — in part because males have fewer "complicating" factors.

"The majority of studies that use mice are only studying the males," Bohannon explains. "Because in all [female] mammals there's an estrus cycle, ... a decision was essentially made by many different people in biology a long time ago that, well, maybe we just won't study the females, because the guys don't have that."

In her new book, Eve: How the Female Body Drove 200 Million Years of Human Evolution, Bohannon begins in the Jurassic era and moves into the current day, exploring everything from why menstruation happens to why female humans are more likely to get Alzheimer's disease.

Bohannon notes that historically, many clinical drug trials involving human subjects omitted female patients who were of child-bearing age, out of concern for the impact on a potential fetus.

"But unfortunately, being of reproductive age is anywhere from, like, 12 or 13, to in your early 50s," Bohannon says. "So that's the majority of our lives. That's a big gap."

Bohannon says that though regulations have shifted in recent years, pharmaceutical companies are not required to go back and redo past experiments — which means "the vast majority" of prescription medicines currently on the market may not have been tested female bodies at all. This could have implications for how well they work for women, trans men and some nonbinary people.

"So effectively, we've been guinea pigs," she says.

Interview highlights

On how female bodies process opioids differently

We now know that opioid drugs are now famously processed different in typical female bodies. It often takes us longer to recover from side effects, or we clear it from our systems too soon and then we feel like we need more. Opioids are common prescription painkillers. ... So while it's true that more men are addicted to opioids because that's a general addiction pattern, women are especially vulnerable and it can really, really, really influence things like pregnancy and postpartum recovery and anything in our lives, really.

On a 1999 study that revealed a difference in how female bodies process anesthesia

They actually had a bunch of men and women included in the study. So that's great. But they didn't set out to test sex differences. They just wanted to know: Is this new special EEG machine ... Is it usefully influential in monitoring anesthesia effectively? And it turned out. Yeah, sure. The machine was kind of fine. But what they really found out is that women come out of anesthesia faster, even if they're the same weight as the guy. They still need a different profile of treatment in anesthesia. And it's actually true that women are more likely to wake up on the surgery table.

On why more women die of heart disease

One of the main reasons that heart disease can be such a killer for so many women is that our symptoms can be different. And that's something that thankfully has gotten some more airtime lately because awareness saves lives. So when you have what we would call a heart attack, in women, it may instead of feeling like that pressure on the chest, that classic model, it may feel more like severe indigestion. Some women report just feeling weirdly anxious with no history of anxiety in their lives.

There are some ways in which most women's cardiovascular systems are slightly more vulnerable. We're slightly more likely to get stroke. That's tied to how we live longer. But for the most part, what's going on, I think, and how vulnerable women are to heart disease today is absolutely that disparity in studying sex differences.

On human menstruation

There are only a handful of species that menstruate the way we do, in other words, that start building up this lining, whether or not there's an incoming potential baby. The thing that's common among all of those is that all of these species, like us, have incredibly invasive placentas. Some placentas are kind of shallow. They kind of sit on the top of the lining of the uterus. Some of them are medium. Ours are the most deeply invasive kind. They penetrate all the way into the mother's bloodstream in that uterine wall. And having it like that has massive impacts throughout the female body.

On the differences between male and female brains

If you manage to have two cadaver brains in your hands, you actually will not be able to tell which is male and which is female. And that's true by almost any measure. Even if you are using microscopes, even if you are using the most careful instruments, the only way to actually do it is to sluice the whole thing down in a blender and sequence the DNA and look for the Y chromosome, because the brain is actually made of many, many different regions. And there are some typical sex differences in some features in some regions, but the differences are so subtle, and even a brain that might have a so-called female typical region would then end up having a male typical other region. You end up with a mosaicism and that means that what human brains really evolved to be is remarkably similar, more similar in many ways, both in structure and in overall functionality than they are for other mammals.

Sam Briger and Seth Kelley produced and edited this interview for broadcast. Bridget Bentz, Molly Seavy-Nesper and Carmel Wroth adapted it for the web.