Scientists assert that domestication has made cat and dog breeds more diverse, yet surprisingly similar to one another. This has serious implications for the health of these animals. At first glance, Persian cats and pugs seem entirely different, separated by 50 million years of evolution. However, when a team led by Abby Grace Drake, a professor of evolutionary biology at Cornell University, scanned 1,810 skulls of cats, dogs, and their wild relatives, they uncovered something intriguing. Many breeds of cats and dogs exhibited striking physical similarities, particularly in skull shape.
Divergence and Convergence
In evolutionary biology, divergence refers to the process by which organisms with a common ancestor become increasingly different over time, while convergence describes how unrelated species develop similar traits due to comparable environmental pressures. In the case of domestic cats, dogs, and many other domesticated species, both intentional and unintentional selection by humans has evidently led to convergence, guiding different species toward the development of similar characteristics. Despite a long history of evolutionary divergence, breeds with flat faces, such as Persian cats and pugs, share similar skull structures.
To investigate how domestication has altered the skull structure of these animals, Professor Drake’s team analyzed 3D scans of skulls from museums, veterinary schools, and digital archives. The dataset included samples of domestic cats like Siamese, Persian, and Maine Coons, as well as over 100 dog breeds with varying muzzle shapes. The analysis revealed that domestication not only diversified the skull shapes of these animals but also caused some cat and dog breeds to resemble each other, converging toward either elongated or flat muzzles. Wild canids (a group that includes dogs, wolves, foxes, and jackals) typically have elongated skulls, while wild felids (which include cats, lions, tigers, and jaguars) display more natural variations. However, domestic cat and dog breeds now encompass a more extreme range at both ends of the spectrum, as reported by the Independent.
The experience of domestication has shown that, with human intervention, even distantly related species can take on similar appearances and suffer in similar ways.
Selection and Its Detrimental Consequences
Selection has exaggerated traits across different species. The human fascination with animals that have flat faces taps into some of our fundamental instincts. We are hardwired to respond to baby-like features such as round cheeks, small noses, and large, low-set eyes. These traits, which are amplified in many flat-faced cat and dog breeds, mimic the appearance of human infants. Among all species, humans are among the most immature at birth, entering the world helpless and dependent on caregivers. In contrast, bred animals can see, hear, stand, and move shortly after birth.
Because human infants are so reliant on adult care, evolution has shaped us to be sensitive to signs of vulnerability. These features, like round cheeks and wide-open eyes, are known as social triggers, prompting caregiving behavior in adults. Thus, pets with these traits are “destined” for human care and attention, but this comes at a cost. Experts have repeatedly noted that selection for extreme physical traits has led to a prevalence of health issues in these animals, including breathing difficulties, neurological disorders, and complications during childbirth. Animal welfare organizations emphasize that animals with severe hereditary health problems should no longer be used for breeding, and that breeder practices need to be strictly regulated.
The takeaway from all this is clear: selection has demonstrated how easily humans can bend nature to their whims and how millions of years of evolutionary divergence can be overturned in just a few decades of artificial selection.