Modern farm environments are profoundly different from the natural habitats of the ancestors of today's farm animals, and through genetic selection, the appearance and behaviour of the animals themselves have also changed. However, the legacy of the ancestors is still obvious, and some apparently bizarre actions are only possible to understand in the light of the evolutionary history of the species. On the other hand, some of the behaviour we can observe in animals in a modern farm or in a laboratory are not part of the normal, species-specific behaviour at all. They may even indicate that the animal is under stress and that its welfare is poor. Distinguishing between these possibilities is one important goal for applied ethology.