I was watching an anthropology show on early humans and it brought up this big beautiful cave in France where they were suprised to find out that people used to congregate at from all over Europe, Africa and Asia annually the suprise part was that this was in a period when people were supposed to be not really communicating at any advanced level and sticking to their isolated little hunter/gatherer clans the relative part is besides trading some ideas and goods, it seems they were mainly there to "dance, drum and party" for about a week straight... traces of very old mushrooms, weed and other intoxicants amongst the stone tools and clothing... the host of the show said that maybe the biological explanation was to spread out the gene pool... I think they did it because thats what people like to do