"Hate often comes and can be triggered by an actual experience of love," said Epley. "When you feel most hate toward somebody else or some 'out' group, it's typically when your 'in' group is feeling really threatened. So people are willing to die, to put their lives on the line, to try to save the life of somebody who's part of their 'in' group. It's really a tight brotherhood with others that seems to inspire the most hatred for others."
To hear more about how love and hatred connect in the mind, watch the full HuffPost Live clip in the video above.