The obvious evolutionary psychology hypothesis behind the imbalanced gender ratio in the iconoclastic community is the idea that males are inherently more attracted to gambles that seem high-risk and high-reward; they are more driven to try out strange ideas that come with big promises, because the genetic payoff for an unusually successful male has a much higher upper bound than the genetic payoff for an unusually successful female. ... a difference as basic as "more male teenagers have a high cognitive temperature" could prove very hard to address completely.

You ask evo-psych why we have a problem, and evo-psych provides the answer. The gender that has a biological reason to pursue low risk strategies - shockingly! - tends to not show much interest in weird, high-risk, high-payoff looking things like saving the world.

Ask evo-psych how to solve the problem then. We already know that women tend to like doing highly visible charitable activities (for signaling reasons). Maybe we should provide a way for people to make little sacrifices of their time and then make it visible over the web. I am thinking of a rationalist social network that allowed people to very prominently (perhaps even with a publicly visible part here on LW) show off how many hours they had volunteered next to a picture of themselves. I once attended an amnesty international letter writing group that was 90% female, for example.

However, remember that association with any radical sounding idea is high-risk compared to association with a less radical but equally charitable sounding idea. Thus I would predict that women will, on average, tend to not get involved with singularitarianism, transhumanism, existential risks, etc, until these ideas go mainstream.