This is in reference to the large number of girls working in my laboratory? 😉
Generally speaking, the numbers of males and females in science, or at least studying science, are fairly equal. There tend to be slight differences between disciplines, however, so arguably in some areas of physics there are more men than women – though there is no physical reason why this should be the case.
It happens that certainly from what I’ve seen, there appear to be slightly more girls doing microbiology. I’m also not sure why this would be? Perhaps my observations are not enough in this, and I would need to look at some national league-tables to be sure that this fact is correct.
Where differences tend to arise between numbers of males and females is as you go up the career ladder to the most senior scientists. On the whole there do seem to be slightly more males than females, but this is something that will hopefully continue to change over time, as the nature of science careers make increasing allowances for women to choose to have children, and also return to good science positions afterwards.