There's a lot of evolutionary processes that don't have to do with having more offspring, but increasing the viability of less offspring. Having kids, no matter the species, is a very costly affair. You could argue that mate selection generally reduces the number of offspring, but increases the viability.

I've read a hypothesis (very much unproven) that having some gay members of a species increases the viability by having more people to care for the offspring without being in mate competition. It's called the gay uncle hypothesis