AFAIK in most (all?) species where females invest more in offspring, males are required to put some extra work in exchange (for example building a nest). It can

AFAIK in most (all?) species where females invest more in offspring, males are required to put some extra work in exchange (for example building a nest). It can't be too much rationality if it happens all over in the nature. The question is whether this carries over to human group/society norms, and I believe it does.