Comments

This study actually is consistent with much primate behavior that seems to be 'altruistic'. Primates live with many relatives, and even the individuals in their groups who aren't relatives are long-term members of the group who interact with each other over and over every day. It turns out that helping your relatives helps yourself, in that you share lots of genes with your relatives, so you end up passing your genes on to the next generation through helping your relatives reproduce. And helping individuals who you know you'll see in the future (relatives or not), can turn out to be helping yourself as well, because primates are smart enough to remember who they 'owe' and who 'owes' them. This is the 'tit for tat' or 'you scratch my back I'll scratch yours' logic of an exchange of favors. It only works if you're reasonably confident that you'll see each other again, and primate groups meet that requirement. So, the 'sharing' monkeys are actually behaving in a self-beneficial manner by choosing to feed themselves AND their relative or 'friend'. More impressive, and unexpected, would be if they chose to feed the relative or friend if that meant sacrificing their own piece of apple.