For a long time, for most aspects of brain function, sex influences hardly mattered to the neuroscience mainstream. The only sex differences that concerned most neuroscientists involved brain regions (primarily a deep-brain structure called the hypothalamus) that regulate both sex hormones and sexual behaviours.
Neuroscientists almost completely ignored possible sex influences on other areas of the brain, assuming that the sexes shared anything that was fundamental when it came to brain function.
Conversely, the neuroscience mainstream viewed any apparent sex differences in the brain as not fundamental – something to be understood after they grasped the fundamental facts. By this logic, it was not a problem to study males almost exclusively, since doing so supposedly allowed researchers to understand all that was fundamental in females without having to consider the complicating aspects of female hormones. To this day, neuroscientists overwhelmingly study only male animals.
To make matters worse, studying sex differences in the brain was for a long time distasteful to large swaths of academia.
Regarding sex differences research, Gloria Steinem once said that it’s “anti-American, crazy thinking to do this kind of research.” Indeed, in about the year 2000, senior colleagues strongly advised me against studying sex differences because it would “kill” my career…
h/t hbd* chick