tl; dr: Normally relatives will care for young since they're more genetically related than to strangers, so they are still helping their genes even though it's not their offspring. But here they also find that members of the species will help the group even if not closely related, because the group itself offers survival advantages from predators, thus it benefits the helper enough to be worth it. They note that the former caring-for-relatives occurs when predators aren't as big an issue, and the latter when it's a dangerous world. Ethnocentric nationalism versus diversity and the (((ever-present predator))), basically. > When there is a survival advantage to group living, the study reveals two ways in which natural selection causes subordinate group members to help with caring for the young of dominant breeders. One possibility applies if the young are closely related, e.g. the siblings of the caregivers, as outlined above. In this situation, the care increases the probability that the genes shared between helpers and receivers of help are spread to the next generation (a mechanism referred to as "kin selection"). > > The second way involves what is known as "individual selection," which is not contingent on relatedness levels. When the altruistic brood care provided results in more young animals surviving, the social group expands. In turn, this increases the survival chances of the caregivers, because it reduces their own risk of falling victim to a predator, for example. It hence increases the probability that they will be able to breed successfully later on. Both selection mechanisms interact positively with each other. > > Which selection mechanism prevails depends on the environmental conditions > > "A key finding of our study is that the environmental context determines which of these two selection mechanisms comes into play, i.e. which one is more significant for the evolution of cooperative breeding," says Irene Garcia Ruiz. If the environmental conditions are favorable (few predators), then kin selection is the more important mechanism selecting for cooperative care. If the environmental conditions are less favorable (more predators), then increasing the survival chances of individuals by raising the number of group members is a more important selection mechanism causing non-parental offspring care.