In Europe, the winters are very very very cold. wild pigs (or maybe pigs in general) have spikes/prickly things in their skin. now in order for them to gain some warmth in the cold european winters, these pigs huddle so they can share their body warmth. now the pigs notice that being too close together creates warmth but also means that other pigs' spikes are penetrating their skin and so blood trickles down these pigs. being too far apart means they can't get much warmth. these pigs then found out the right combination of being close enough for maximum warmth without being hurt by other pigs.

the moral of this story? well you figure it out. but i must say, i've NEVER fought with my friends and this is the reason. by the way, this story is quite fitting as it is **** cold right now where i am.