We know at the present time that all animals, beginning with the ants, going on to the birds, and ending with the highest mammals, are fond of plays, wrestling, running after each other, trying to capture each other, teasing each other, and so on. And while many plays are, so to speak, a school for the proper behavior of the young in mature life, there are others which, apart from their utilitarian purposes are, together with dancing and singing, mere manifestations of an excess of forces— “the joy of life,” and a desire to communicate in some way or another with other individuals of the same or of other species—in short, a manifestation of sociability proper, which is a distinctive feature of all the animal world.
- Kropotkin, Mutual Aid: A Factor of Evolution
