"Do we assess others based on similarity, on their devotion to the same political beliefs, TV shows and sports teams [Twitter]? Or do we focus instead on their closeness to us, on whether or not they’re a sibling or a third cousin or a distant friend [Facebook]? This might seem like a minor mystery, but it has some major implications for social cognition. Are we clannish creatures, obsessed with bloodlines and kinship? Or are we more interested in finding a group that shares our peculiar passions and opinions?" Jonah Lehrer at The Frontal Cortex says our primate past causes us to be a rather clannish species.