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Intensive breeding practices have led to notable similarities in skull shapes between breeds such as pug dogs and Persian cats, resulting in distinct “smushed” faces. This evolution has made them more alike than they are to many other dogs and cats.
Recent research conducted by teams at Cornell University and Washington University has revealed intriguing instances of convergence—the phenomenon where unrelated species develop similar features due to shared environmental pressures. This marks a significant finding in understanding domesticated species.
The study highlights impressive examples of convergence not only within each species but also between them. The emphasis is particularly on breeds featuring brachycephalic characteristics, commonly known as those with short faces.
Through human-induced artificial selection, certain breeds of cats and dogs have reached such a degree of similarity that they resemble one another more closely than they do to members of their respective species. This degree of convergence had not been documented before in domesticated animals.
Upon examining the skulls of brachycephalic dogs and cats, researchers noted a strikingly comparable morphology among the breeds from these distinct species.
According to Abby Drake, a senior lecturer at Cornell University and co-author of the study, “Persian cats, as well as pug and Pekingese dogs, share remarkably similar skull shapes. Their flat faces are complemented by muzzles and palates that tilt upwards in the same manner.”
This convergence is observed repeatedly within each species; in dogs, it is evident among bulldog breeds and also among Asian dog breeds such as Pekingese and Shih Tzu. For cats, comparable traits can be found in breeds like Persian, Himalayan, and Burmese.
Convergence often signifies the emergence of a successful adaptation in natural selection contexts, as seen with features like wings in birds, bats, and insects. In domesticated animals, rapid evolutionary shifts may provide unique insights into evolutionary mechanisms, as noted by Drake.
The research team meticulously mapped and compared skull shapes, uncovering these similarities despite the fact that the ancestorial forms of cats and dogs were distinctly different. Dogs emerged from wolves, larger creatures characterized by long muzzles, while cats evolved from wildcats—smaller animals with shorter faces.
Drake remarked on this intriguing phenomenon: “Despite starting from different evolutionary points, the application of similar selection pressures by humans has led these species to evolve comparable appearances.”
Through artificial selection, an extraordinary variety has arisen in both cats and dogs, although dog breeds exhibit even greater divergence. Notably, dogs are more diverse than all members of the Carnivora order combined.
Drake stated, “This significant evolutionary variation within a species, evolving in a relatively short time frame, is remarkable. Typically, evolution spans millions of years, but our interventions with dogs have expedited this process immensely.”
The study similarly indicates that domestic cats exhibit more diversity than the entire Felidae family, which comprises 41 species.
However, these extremes of breeding have problematic implications. Drake cautioned that brachycephalic breeds face serious health challenges related to breathing, eating, and birthing, which would hinder their survival in natural habitats.
In their investigation, researchers collected three-dimensional data on skull structures through CT scans of domestic cats, dogs, as well as wildcats and wolves. They also included representatives from various Carnivora species, such as weasels and walruses. The specimens were gathered from veterinary institutions, museum collections, and MorphoSource, a digital repository for natural history.
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