Women tend to act heroically within their own moral universe, regardless of whether anyone else knows about it - donating more kidneys to nonrelatives than men do, for example. Men, on the other hand, are far more likely to risk their lives at a moment's notice, and that reaction is particularly strong when others are watching, or when they are part of a group.
Sebastian Junger, Tribe: On Homecoming and Belonging
genders, men, women