> the things people are willing to do in order to fit into a group

Given our evolutionary history as social animals, this is expected. The genes (and memes, in the Dawkinsian sense of the word) for alienating oneself from the tribe and going solo were less successful than the those for remaining in the tribe. We can reasonably expect such adaptations to include sucking up to alphas to avoid being banished from the tribe, being distressed when outside a group, and feeling good when in a group.