How would someone explain the evolution of adaptation through being social?

The topic is on the chapter summaries below explain the kinds of evolutionary processes involved in the rise of different kinds of primates? What is unique about primate adaptations in general? What are the kinds of variation we see?

think beyond the Latin names. Think about processes and relationships among the species we’re discussing.  Latin names can be confusing. But remember the key point: the first word is the genus and shows you which species are related to each other; the second name is the species.

How would someone explain the evolution of adaptation through being social? After all, caring for helpless infants is time-consuming and uses energy. A female animal could spread more of its genes by laying eggs and leaving them, but primates tend to have one birth per pregnancy and then put a lot of work into raising the infant for several years. What is the adaptive advantage of that?