What's the real reason for the gender gap in STEM fields?

I am continuously fascinated by research about why so few women are in engineering. It is a perplexing issue. Here is a new look at why women & men make different career choices.

"The survey data showed a notable disparity on one point: That men, relative to women, prefer to work with inorganic materials; women, in general, prefer to work with organic or living things. This gender disparity was apparent very early in life, and it continued to hold steady over the course of the participants' careers.

Benbow and Lubinski also found something else intriguing: Women who are mathematically gifted are more likely than men to have strong verbal abilities as well; men who excel in math, by contrast, don't do nearly as well in verbal skills. As a result, the career choices for math-precocious women are wider than for their male counterparts. They can become scientists, but can succeed just as well as lawyers or teachers. With this range of choice, their data show, highly qualified women may opt out of certain technical or scientific jobs simply because they can."

I personally believe that because engineering jobs developed in a male-only environment and women were not clamoring to get in (because of the above sited reason), women often feel like they are not a good fit and therefore it continues to be a male dominated environment.