How Dogs and Cats Are Evolving to Look Alike and Why It's Humans' Fault

Domestication has led some animal breeds to resemble one another, with convergence towards either long or flat faces.

- Grace Carroll

Domestication has made cats and dogs more diverse, but also curiously alike—with serious implications for their health and welfare, new research shows.

At first glance, Persian cats and pugs don't seem like they'd have much in common. One's a cat, the other's a dog, separated by 50 million years of evolution. But when evolutionary biologist Abby Grace Drake and her colleagues scanned 1,810 skulls of cats, dogs and their wild relatives, they found something strange. Despite their distant histories, many breeds of cats and dogs show striking similarity in skull shape.

In evolutionary biology, divergence is a common process. In simple terms, divergence is where two organisms that share a common ancestry become increasingly different over time, while convergence means becoming more similar. As populations of animals split and adapt to different environments, they gradually develop new traits, a process known as divergent evolution.

This is one of the main ways new species form different traits, causing populations to evolve along separate paths. But sometimes, evolution can take a different direction. Convergence happens when unrelated species, shaped by similar pressures, independently evolve similar features.

In the case of domestic cats, dogs and many other domesticated species, intentional and unintentional selection by humans seems to have created convergence, accidentally steering different species toward similar traits.

Despite a long history of evolutionary separation, flat-faced breeds like the Persian cat and pugs share similar skull structures.