Finally wrangling with the complexity of female bodies benefits us all

Women are not just “little men.” And yet, medical science has long been comfortable acting as if they are, focusing research on male rodents and men because they lack the complex hormonal cycles of females, and then transferring any results to women. Fortunately, in recent decades there has been widespread recognition that neglecting to study the female body in this way is harming women's health by creating treatments that do not work as well for them as they do for men.

Now the study of how sex chromosomes shape our immune system has brought another twist to the story: ignoring the complexity of the female body has harmed not just women, but everyone (seeWomen have a stronger immune system, and now we know why“).

Much of the problem comes from the strength of averages. Statistical tools give us the ability to smooth out variations and make important discoveries from data. But when used excessively, they erase signals that can teach us a lot. Women generally have stronger and more responsive immune systems than the average man, demonstrating, for example, a more robust response to vaccines and lower mortality rates from infectious diseases in older age.

But by grouping male and female medical research participants together in one place—which is admittedly better than not studying women at all—sex differences in response to antiviral drugs and new vaccines are being erased and lost. Ultimately, this can result in the average woman receiving too high a dose of medication, while the average man is prescribed too little for optimal treatment. Research into how these differences may affect transgender people has received even less attention.

But researchers are finally figuring out how the X chromosome and hormones underlie these sex differences, and the findings from this work should allow us to better personalize treatments for everything from long-term coronavirus infections to cancer—for everyone. We all benefit from abandoning the concept of “little people.”