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19 May 2025
While dogs have been our companions for thousands of years, recent studies reveal that our preferences have drastically shaped their evolution, especially regarding their skulls. Surprisingly, despite their vast differences in size, function, and breed, many dogs now share strikingly similar skull shapes to those of another beloved animal: cats.
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Research conducted by scientists at Cornell University and Washington University has uncovered a surprising link between dogs and cats, specifically their skulls. Our human preference for baby-like features, like large eyes and round heads, has led to an unexpected phenomenon known as “copycat evolution.” Despite being separated by over 50 million years of evolution, dogs and cats, particularly brachycephalic breeds, have evolved nearly identical skull shapes due to similar selective breeding practices.
Brachycephalic dogs refer to dogs with short, broad heads and flat faces, such as Pugs, Bulldogs, and Pekingese. Like their flat-faced feline counterparts (e.g., Persians), these dogs have been bred for their “cute” features—large eyes, compact heads, and short muzzles. These features trigger a nurturing instinct in humans, and breeders have selected for these characteristics over generations. However, this love for baby-like faces has unintended consequences.
In a study published in Proceedings of the National Academy of Sciences, researchers analyzed over 1,800 skulls from domestic and wild dogs and cats. What they discovered was noteworthy: dogs and cats, particularly those with short muzzles, are evolving increasingly similar skull shapes, despite their vastly different evolutionary histories.
For example, breeds like the Persian cat and Pug dog now share remarkably similar skull features, despite having evolved from very different ancestors.
Wild dogs, like wolves, have longer, more streamlined muzzles. In contrast, due to selective breeding, domestic dogs have undergone significant skull changes, evolving from these long-muzzled ancestors into short-faced breeds. Interestingly, cats, especially domestic ones, didn’t change as drastically in their muzzle length but evolved changes in the angle of their foreheads and muzzles.
This means that while dogs needed significant genetic changes from wild wolves to brachycephalic breeds, domestic cats, with their naturally shorter muzzles, didn’t need to undergo as many changes but developed similar skull shapes due to similar selective pressures.
While these dramatic skull changes have made our dogs and cats look endearing, they’ve also led to health complications—brachycephalic breeds, whether canine or feline, often suffer from breathing, eye, and dental problems. The flattened face and shortened airways in these breeds create difficulties for normal breathing, leading to conditions like brachycephalic obstructive airway syndrome (BOAS).
While the evolving skull shapes of dogs and cats are fascinating, the consequences of these breeding practices are now raising serious concerns. There’s increasing pressure to reconsider the breeding of extreme brachycephalic breeds for animal welfare reasons. Many animal advocacy groups are calling for a reduction in the number of these extreme breeds due to the health problems they often face.
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In the grand scheme of evolution, it took nature millions of years to shape the distinct differences between wild cats and dogs. However, it took only a few centuries of selective breeding for humans to blur these lines and create new dog breeds. The next time we marvel at the cuteness of a brachycephalic dog or cat, it’s important to remember that while these animals may look adorable, the evolution that created them has come with a price — one that might require us to rethink our breeding practices for the future.
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