Many people claim that they are either a cat person or a dog person. The two species are often considered to be so completely opposed that you’re either Team Cat or Team Dog. If you were to put me on the spot, I’d probably go with Team Cat, but I must confess that I do have a bit of a soft spot for the slobbering, exuberant hound.
But what makes dogs and cats different, and has our influence meant that these differences are gradually disappearing?
Cats and dogs behave differently because of their innate species-specific characteristics
They have been separated by evolution for over 50 million years, and over this long period of time the two species became very different.
Dogs are a pack animal, and this makes them a highly social species. Their survival depends on the rest of the pack. Dogs therefore had to develop skills of cooperation and needed to be able to form strong social bonds. The domesticated pet dog retains many of these social traits and will look to their human caregiver as a member of their pack. They have a strong need for companionship and connection with their owner to help them feel safe and secure.
Pet cats have evolved from the African wildcat, a solitary species that needed to fend for themselves. Cats did not need to learn the art of cooperation or teamwork in order to survive. Instead, they had to depend on developing skills like hunting and guarding their territory to keep themselves fed and safe.
Dogs feel most reassured when they have their familiar pack members around them. For the domesticated dog, this means us. Cats on the other hand feel most comfortable when they are in familiar surroundings. Unlike dogs, they don’t necessarily rely on their owner for reassurance in unfamiliar situations. Today’s cat is considered ‘socially flexible’, meaning they can adapt to social situations, but they are still not typically as reliant on social interaction for their well-being as dogs are.
While dogs and cats still retain many of their wild ancestor’s traits, selective breeding has helped to engineer them into the pets we see today
It’s believed that humans may have begun to deliberately selectively breed dogs around 9000 years ago in the Neolithic period – although the relationship between humans and their ancestors is almost certainly much, much older. We began by developing breeds of dog by artificial selection that would be better suited to helping humans with hunting. Other breeds soon followed, developed for other purposes such as pulling sleds, herding or guarding. In the Victorian period, a focus on breed standards and the ‘look’ of the dog began to firmly establish itself, with the appearance of dog shows and hobbyist dog breeders.
While humans have had a long relationship with cats, dating back some 10-12,000 years, we have generally left their breeding up to natural selection. Humans did not deliberately pair cats to produce offspring with human-engineered traits, in the way we did with dogs. Cats that could adapt to human environments were more likely to survive and reproduce, so cats gradually became more domesticated on their own. This all changed when those breed-obsessed Victorians began setting up cat shows and breed registries to make the breeding of cats a popular hobby. Modern cat breeds are therefore relatively new, emerging only within the last 150 years or so.
The selective breeding of dogs and cats may have had the surprising and perhaps unintended effect of making these two very different species more similar than ever before
A recently published paper (Drake et al. 2025) compared the skull shapes of domestic dogs and cats, as well as their closest living wild relatives. The researchers collected over 1800 skulls and analysed measurements using CT scans. Their sample included 148 domestic cats and 677 domestic dogs, including flat-faced or ‘brachycephalic’ breeds such as Pugs, Pekinese and Persians. The researchers also examined hundreds of skulls from wild dog and cat species.
The researchers looked for evidence of similarities or differences in the way these skulls have developed, either through the process of natural selection in the wild or through artificial selection by humans. They found that the selective breeding of domestic dogs and cats has led to a strange phenomenon, whereby these domesticated breeds have developed skulls more similar to each other than to those of their own species living in the wild.
The study considered the evolutionary process of ‘convergence’
Convergent evolution occurs when unrelated organisms independently evolve similar traits or structures due to adapting to similar environmental challenges. One example of convergence is the way dolphins and sharks have evolved to have a very similar streamlined body shape. Dolphins are mammals and sharks are fish, so they are not closely related. Yet both developed the same evolutionary ‘solution’ to the problem of needing to be effective predators in an aquatic environment.
When the researchers looked at the canine and feline skulls, they found evidence that convergence had occurred due to selective breeding by humans. This is the first time this process has been documented in domestic species. Over the last 150 years of artificial selection, humans have, consciously or unconsciously, been creating pets that have “baby-like” features. Pets with large eyes, small noses, and round faces trigger a strong, innate human reaction to caregiving, because these features are similar to those found in human infants. Selective breeding has led to many breeds of dogs and cats that look strikingly similar, converging on these “baby schema” features.
Flat-faced, or ‘brachycephalic’ breeds of dog and cat are where the researchers saw the most evidence of this type of convergence. Flat skulls have been bred into domestic dog and cat breeds relatively recently and aren’t seen to naturally occur in the wild. Humans have created this skull shape because it is aesthetically pleasing to the human eye.
But breeding animals to make them look cuter can be very damaging for their health
There is now a large amount of research to show that dogs and cats with extremely flattened skulls have difficulties with breathing. They find it harder to cope with exercise and with heat because of their reduced ability to take in enough oxygen. They can also develop problems with their eyes, teeth, facial skin and neurological system. These are very serious animal welfare concerns, affecting the quality of life of millions of pets around the world.
Frustratingly, the problems experienced by brachycephalic pets are entirely preventable. We can reverse this change in skull shape through better breeding practices, yet the popularity of brachycephalic animals seems to be growing. It’s also a trend that we’ve been seeing in rabbits, too.
To improve the welfare of our pets, humans will need to start prioritising animal welfare over our current human preconceptions of what is cute or desirable
And it’s not just breeders who will need to lead the change. Breed registries like the Kennel Club, vets, the media, and the public need to become aware of the crisis affecting our pets and proactively change what we want to see in our much-loved companions.
Perhaps it may be advantageous for dogs and cats to be selective bred, in ways that make life as a pet better. For example, perhaps dogs could experience better welfare as pets if they were not so prone to separation anxiety due to their species-specific need for constant companionship. Perhaps a more socially adapted cat would be better able to cope in a domestic environment. These selective breeding manipulations must be carefully considered, as there can be serious consequences if we get things wrong. We must make sure that the changes we are breeding into animals are in the animal’s favour, not just ours. One thing is for certain; we can no longer base the selective breeding of pets on looks alone. When we popularise certain breeds, we need to be aware of the potentially negative consequences for the animal in doing so.
References and Further Reading:
Drake, A.G., Revell, L.J., Klingenberg, C.P., Lattimer, J.C., Nelson, N.C., Schmidt, M.J., Zwingenberger, A.L., Moyer, J.K., Losos, J.B. (2025) ‘Copy-cat evolution: Divergence and convergence within and between cat and dog breeds’, Proceedings of the National Academy of Sciences USA, 122 (18) e2413780122.
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