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Brachycephalic Breeds: A Study of Convergence in Cats and Dogs
Intensive breeding practices have led to a fascinating evolutionary phenomenon in domesticated animals, particularly in breeds like pugs and Persian cats. This has resulted in unusually similar skull structures and facial features, often referred to as “smushed” faces, marking a striking example of convergence between unrelated species.
Researchers from Cornell University and Washington University have traced the evolutionary journey of these breeds, revealing significant parallels in their development. Convergence, the process whereby different species evolve similar traits due to comparable selective pressures, was historically observed in wild species but has now been documented among domesticated ones, particularly in breeds with brachycephalic traits.
The study highlighted that breeds such as Persian cats and various breeds of brachycephalic dogs have evolved to the point where their skull shapes are remarkably analogous. “Both Persian cats and brachycephalic dog breeds exhibit similar skull traits, characterized by flat and short faces, with elevated muzzles and palates,” explained Abby Drake, a senior lecturer at Cornell and one of the study’s authors.
This convergence isn’t limited to just a few breeds; it also occurred multiple times independently within both species. For instance, within dogs, typical brachycephalic breeds like bulldogs and certain Asian breeds such as Pekingese and Shih Tzu have developed similar traits. Likewise, in the feline world, breeds like the Persian, Himalayan, and Burmese display comparable characteristics.
When examining how physical traits develop through natural selection—like wings in flying species—a successful evolutionary adaptation is often indicated. However, in domesticated animals, the rapidity of these developments can shed light on the evolutionary process itself. The research team meticulously mapped and compared skull shapes, unveiling the similarities despite the distinct ancestral backgrounds of cats and dogs. Dogs have evolved from wolves, while cats originate from wildcats, presenting an intriguing picture of evolutionary adaptability.
“Though their starting points were vastly different, the same selective pressures imposed by human interventions have led them to evolve similarly,” Drake noted. This drastic transformation in both species is considerable, especially given that common dog breeds display a wider variance than the entire Carnivora order.
Drake remarked on the astonishing evolutionary variance observed within dogs over a relatively short evolutionary timeline. “Typically, evolutionary change spans millions of years, yet we’ve achieved significant contrasts in dogs through selective breeding,” she stated.
The research showed that cats, too, reveal greater diversity as a species compared to the broader Felidae family, which encompasses 41 distinct species. However, this rapid development comes at a cost; many brachycephalic breeds suffer from various health complications related to their altered anatomy, including issues with breathing and giving birth, which would hinder their survival in the wild.
For their analysis, the researchers utilized three-dimensional skull measurements obtained from CT scans of domestic cats and dogs, as well as their wild counterparts—species of Canidae and Felidae—culminating in a broad examination of diverse animal anatomy. Data was sourced from veterinary institutions and museum collections, along with digital archives.
More information: Drake, Abby Grace et al, “Copy-cat evolution: Divergence and convergence within and between cat and dog breeds,” Proceedings of the National Academy of Sciences (2025). DOI: 10.1073/pnas.2413780122.
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phys.org