I do think it's primarily cultural. As so many gender differences are, though, it's hard to get to nature versus nurture dimensions definitively with every trade. But certainly, girls and young women want to have every skill that's required for a particular position before they will volunteer for it.
If you have a team sitting around a table, and there's a project put out, we so often see young men, if they know about 60% of what needs to be done, putting up their hands and saying, “I'd like to try it”, whereas women are sitting there wanting to feel they've got 100% or 120% of the required skills before they volunteer for it. It goes right through youth into maturity.
I think we obviously need to have intervention. Some of it is probably happening in the classroom; some of it is happening at home. We need to be extremely aware of this gender-based tendency and need to start intervening at a very young age to encourage girls to take risks and to try things they're not necessarily certain they can succeed at.