There's been a male tilt to biomedical research for a long time.
The National Institutes of Health is trying to change that and is looking to bring gender balance all the way down to the earliest stages of research. As a condition of NIH funding, researchers will now have to include female and male animals in their biomedical studies.
As late as the 1990s, researchers worried that testing drugs in women who could be pregnant or become pregnant might lead to birth defects, so experimental drugs were mainly tested in men. Research in animals followed the same pattern.