It's possible.

Why are you bringing it up, though? As an aspiring rationalist, I believe it should be possible in principle to discuss whether one sex is more rational than the other, on average. However, it makes me feel uncomfortable that a considerable number of people here feel the need to inject the topic into a conversation where it's not really relevant. If I were a woman, I can imagine I would feel more hesitant to participate on Less Wrong as a result of this, and that would be a pity.