Because fields like mathematics are not very attractive to women, it carries the social stigma of "geek" and "loser" and we know that women buy into stupid things like what other people think. So if we look at how many women go in and how many women come out, if the numbers are the same then we can say that yes, women are just like men when it comes to sciences, at least for the few that make it through the grinder.
Unfortunately, I have found information that proves YOUR point, not mine.
https://womenandmath.files.wordpress.com/2008/01/proportions.jpg
The chart summarizes this information:
http://ec.europa.eu/research/science-society/pdf/she_figures_2006_en.pdf
If we look at this chart we see that although more women get accepted into the sciences, they don't make it when it comes to the workplace by a massive margin. As the level of difficulty increases, the less women you will see in that field.
Therefore women can't cut it when it comes to pure logic, or there is something else that makes them unreliable. Maybe they just can't meet the demands on them when it comes to actual work.
There's still more to look into. That's only the situation in Europe which is more influenced by men. America, the world's shopping mall, will have different statistics. Looking for those.