Dogs don't like cats? Maybe that should be "cats don't like dogs", since it's usually the cat that ends up running away (not always, there are some wimpish dogs out there). But both statements are generally true: most cats don't seem to have much time for dogs and dogs are usually happy to chase anything that is running away, whether that happens to be a cat or a squirrel. That's not to say that a cat and dog can't make friends, or become part of each other's extended "family" – but they would have to work at it. Or rather, we (their owners) would.

The phrase "fight like cat and dog" must have some truth in it. It's certainly been in common use for more than a century, and may be much older than that. Nowadays it's rare to see an actual cat and an actual dog engage in anything more than a brief skirmish – so how did the phrase ever become established?

Like so many aphorisms, it's something of an anachronism. Even as recently as the 19th century, dogs and especially cats were not looked after as well as they are today. Both were allowed to roam the streets, and in considerable numbers, since there was little check on the rate at which they reproduced (apart from the grim sack/river tradition).

So are cats and dogs natural enemies? Well, they probably were once.

Competition over scarce scraps of food would have led to frequent fights. A dispute between two dogs is often resolved without actual fighting, since dogs have inherited a sophisticated set of signals from their pack-dwelling ancestor, the wolf, that enables them to signal their intention to back down if they consider their opponent too fearsome. Cats, being descended from solitary predators with little need to communicate face-to-face, lack such abilities, and are generally much more circumspect than dogs when they're deciding whether or not to join an affray. Evolution has not provided either species with any capacity to communicate with one another, so close-combat fighting is more or less inevitable when neither is prepared to run.

Their styles of fighting are also completely different – cats prefer to use their sharp claws (kept that way by being pulled back into sheaths when not required), whereas dogs, who continually blunt their claws by using them for traction when running, persistently try to bring their teeth and powerful jaws into play. Both like to intimidate their opponent vocally, by barking (dog), yowling, hissing and spitting (cat) and growling (both). As a result, once a fight between the two has started, they are often long drawn-out, noisy affairs that can attract a lot of attention.

So are cats and dogs natural enemies? Well, they probably were once. In terms of their relationship with mankind, cats are the interlopers. Dogs were originally domesticated by our hunter-gatherer ancestors, at least 15,000 years ago, possibly longer. Whether they were "man's best friend" in those early days is anybody's guess, but by the time cats came along they were playing a big part in our lives, hunting alongside us, guarding our houses, herding our flocks, even keeping us warm at night.