Scientists Say Dogs And Cats Are Looking More Alike. What’s Behind This Change?

Domestication has led to increased diversity in cats and dogs, yet they’ve also become surprisingly similar—something that could significantly impact their health and well-being, new research reveals.

At first sight, Persian cats and pugs appear vastly different. One is a cat, the other a dog, with a 50 million-year evolutionary gap between them.

However, when evolutionary biologist Abby Grace Drake and her team scanned 1,810 skulls from cats, dogs, and their wild ancestors, they discovered something unusual. Despite their long-separated evolutionary paths, many cat and dog breeds share remarkable similarities in skull shape.

How Evolution Shapes Species Over Time

In evolutionary biology, divergence is a typical process, where two species with a common ancestor grow more distinct over time. On the other hand, convergence refers to species becoming more alike. As animal populations separate and adapt to different environments, they gradually acquire new traits, a phenomenon called divergent evolution.

This is a primary way new species develop distinct traits, leading populations to evolve along separate paths. However, evolution can also take a different turn.  Convergence happens when unrelated species, influenced by similar factors, independently develop similar characteristics.

For domestic cats, dogs, and many other domesticated animals, both intentional and unintentional human selection appears to have caused convergence, unintentionally guiding different species toward similar traits.

Even with a long history of evolutionary separation, flat-faced breeds such as Persian cats and pugs have similar skull structures.

How Domestication Has Shaped Skull Structures

To explore how domestication has altered skull structure, Drake and her team examined 3D scans of skulls from museum collections, veterinary schools, and digital archives. Their dataset featured domestic cats, including Siamese, Maine Coon, and Persian breeds, alongside over 100 dog breeds, ranging from short-muzzled dogs like pugs to long-muzzled breeds like collies.

Their research revealed that domestication has not only expanded the diversity of skull shapes beyond that of wolves and wildcats, but has also caused some cat and dog breeds to resemble each other, converging toward either long or flat faces.

Wild canids, which include dogs, wolves, foxes, and jackals, typically have a similar elongated skull shape, while wild felids, such as domestic cats, lions, tigers, and jaguars, show more variation.

However, domestic breeds from both species now exhibit a more extreme range of skull shapes at both ends of the spectrum. This trend is evident in the creation of cats bred to resemble XL bully dogs.

Domestication has long demonstrated that human intervention can cause even distantly related species to look, and sometimes suffer, in similar ways.

How Human Preferences Shape Animal Traits and Health

Selective breeding has amplified certain traits across species. Many human-driven changes can push animals beyond what their bodies can naturally handle. For example, chickens bred for meat often carry 30% of their body weight in breast muscle, leading to heart and lung issues.

The human preference for flat-faced pets taps into some of our most primal instincts.We naturally respond to infantile features like rounded heads, small noses, and large, low-set eyes. These exaggerated traits in flat-faced cat and dog breeds resemble the appearance of human babies.

Humans are among the most altricial species, meaning we are born helpless and reliant on caregivers for survival, a trait we share with puppies and kittens. In contrast, precocial animals can see, hear, stand, and move shortly after birth. Due to our dependence on adult care, evolution has shaped us to be sensitive to signs of vulnerability and need.

These cues, such as the rounded cheeks and wide eyes of babies, are known as social releasers. They prompt caregiving behaviors in adults, like speaking in higher-pitched tones or providing parental care.

An example of this in non-human animals is seen in herring gulls (a type of seagull). Their chicks instinctively peck at a red spot on the parent’s beak, which triggers the adult to regurgitate food.

This red spot serves as a social releaser, ensuring the chick’s needs are met at the right moment. Similarly, domesticated animals have essentially co-opted these ancient caregiving mechanisms designed for human offspring.

While these traits help pets gain human care and attention, they also come with a cost.

The Impact of Selective Breeding on Cats and Dogs

The UK government has tasked its Animal Welfare Committee with providing independent expert advice on emerging animal welfare issues. In reports published in 2024, the committee expressed serious concerns about the impact of selective breeding in both cats and dogs.

The reports emphasized that breeding for extreme physical traits, such as flat faces and exaggerated skull shapes, has led to widespread health problems, including breathing difficulties, neurological disorders, and birth complications.

The committee recommends stopping the use of animals with severe hereditary health problems for breeding and urges stricter regulations for breeders. Without these changes, many popular breeds will continue to suffer from preventable, life-shortening conditions.

Selective breeding demonstrates how easily humans can shape nature according to their preferences, and how rapidly millions of years of evolutionary separation can be overridden by just a few decades of artificial selection.

By selecting pets with features resembling our own infants’ faces, we have often, unintentionally, chosen traits that are harmful to the animals. Understanding the forces driving convergence between species serves as a reminder of the powerful—and sometimes harmful—role we play in shaping these traits.

Read the original article on: Sciencealert

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