Arunas L. Radzvilavicius, writing for The Conversation:
Even initially uncooperative societies in which everyone judged each other based mostly on their own selfish perspectives, eventually discovered empathy – it became socially contagious and spread throughout the population. Empathy made our model societies altruistic again.
An interesting study, and a terrific resource on the topic of empathy. So many rabbit holes to go down.