Women were first allowed to compete in marathons in 1972. In 1972 the men’s record was 2:10:30. The current record is 2:00:35 which is about an 8% difference. Pretty close to the difference between men and women currently.
The first women’s record was 3:40:22 and the current women’s record is 2:11:53.11 which is 40% faster.
Once funding for women’s athletics reaches parity and once girls are encouraged into athletics as much as boys, then we will see if the ladies catch up. So far they’re doing a pretty good job catching up, and you can’t look at one current window in time and say you have the answer, you need to look at trends.
That’s not my theory. That’s the data.
One interpretation could be that women were constantly engaged in strenuous endurance activities and so through evolution built up tolerances against exhaustion that at least rivals if not exceeds that of men. And one historical activity that used a lot of stamina and took a lot of tolerance against fatigue was the way in which ancient humans hunted.
That’s not what a theory is, it’s a hypothesis at best, hope that helped.