I find that women look for a deeper meaning in any comment (from men or women). Men normally are not that perceptive, and are likely to ignore anything. Of-course nothing applies universally. I believe this difference makes the biases keep on growing.
If a field is not considered good for girls, the girls will not ignore the comments made by other people, and avoid going into the field, while boys will mostly ignore all comments and go head on with it. I guess it goes with our bone-headedness.
I believe that initially women were among the pioneers because there was no such perception. But when somehow this misconception has come about, and it will make it difficult to improve their participation.