[alancalverd (OP)]

Dogs come in a huge range of sizes, shapes and colours, but we assign them all to one species. Selective breeding has produced breeds that hardly resemble wild dogs or wolves - indeed  many that would probably not survive without human assistance.

Cats, foxes, badgers, and many other medium-sized quadrupeds, are based on the same general form as dogs.

If you take your young mutt to a dog park where he can run free with others, it's pretty clear that he recognises everything from a chihuahua to great dane, whippet to St Bernard, as a dog, and at such long range that it can only be by sight. But unless he has read the Kennel Club breed standards book, he won't have seen many quadrupeds apart from his parents and siblings, and there's not a lot of morphological difference between, say, a miniature pomeranian and a fluffy cat. But somehow Rover classifies them all as canis familiaris, just as we do.

How? Why?

[chris]

Some aspects of dog cognition were covered in this recent Naked Scientists programme: https://www.thenakedscientists.com/podcasts/naked-scientists/dogs-life-intelligence-and-inbreeding

There's also one component of that show that explores whether dogs can understand emotions, which is worth a look (and a listen!)