Mark P. Henderson

Evolution of the domestic dog

Two separate shifts in scientific opinion about the domestic dog have happened during the past few years. It’s interesting to consider them together.

One shift came from a detailed molecular genetic study of canines, which revealed such a close similarity between the domestic dog and the wolf that – according to the authors – the dog should no longer be classed as a separate species. It should be regarded as a subspecies of wolf. Using genetic similarity as the basis for taxonomy – which is highly reasonable – would, for consistency, compel us to regard chimpanzees, bonobos and humans as subspecies of a now-extinct common ancestor. At present they’re labelled not only as separate species, as dogs and wolves were before the molecular genetic study, but even as separate genera. It seems we regard the place of our own species in the biological world as unique, despite a wealth of scientific evidence to the contrary. By the same token, many of us seem reluctant to accept the changed status of “man’s best friend” as just a kind of wolf.

The other shift came from a behaviourist study and is less “hard-science” than the molecular genetic one; nevertheless it’s intuitively convincing. According to these findings, the eyes of the domestic dog have evolved to resemble those of human infants in their capacity to appeal to our emotions. Anyone who’s lived with a dog knows how that loving gaze can persuade us to feed the animal as well as demonstrate affection. Those eyes serve the domestic dog very well.

This behaviourist finding raises the question: how, during the subspeciation process, did one group of wolves contrive to evolve those engaging eyes? The broad answer would be that animals with expressions more likely to engage our positive emotions would be at a selective advantage if they lived in close association with humans, depending on them for food and shelter. This is almost certainly the case, but it begs the question: in what, exactly, does the engaging expression consist and how did it develop?

If you’ve ever been face to face with a wolf (I have – in a wildlife park, with a nice high security fence between us), you’ll know how the animal can stare you out of countenance. The wolf’s eyes aren’t exactly hostile or menacing, but when they fix on you they’re not loving and faithful either. Far from it. One friend who’s interacted with wolves without a security fence declared that these animals “stare into your soul”. I know what she meant. Both the wolf and the domestic dog are capable of keeping their eyes on you for long periods of time, but the messages we see in those eyes are quite different.

How did the one turn into the other?