Why do cats and dogs look alike?

Persians and pugs may not seem to have much in common at first glance. One is a cat, the other a dog. They are separated by 50 million years of evolution. But when evolutionary biologist Abby Grace Drake and her colleagues scanned 1,810 skulls of cats, dogs, and their wild relatives, they found something strange. Despite their distant histories, many breeds of cats and dogs share striking similarities in their skull shapes.

According to Popular Science Turkish, divergence is a common process in evolutionary biology. In simple terms, divergence is when two organisms that share a common ancestor become different over time. Convergence is when they become more similar. As animal populations divide and adapt to different environments, these organisms gradually develop new characteristics, a process known as divergent evolution.

This is one of the main ways that new species acquire different traits, causing populations to evolve along separate paths. But sometimes evolution can go in different directions. Convergence occurs when similar traits evolve independently in two unrelated species under similar pressures.

In the case of domestic cats, dogs, and many other domesticated species, deliberate and unintentional human selection appears to have accidentally driven different species toward similar traits, creating convergence.

Despite a long history of evolutionary separation, flat-faced breeds such as Persians and Persians share similar skull structures.

To investigate how domestication has shaped skull structure, Drake and his colleagues analyzed 3D skull scans from museum specimens, veterinary schools, and digital archives. Their dataset includes domestic cats, such as Siamese, Maine coon, and Persian, as well as more than 100 breeds of dog, from short-nosed dogs, such as pugs, to long-nosed dogs, such as Scottish sheepdogs.

Scientists’ findings suggest that evolution has not only increased skull shape diversity, pushing it beyond the skull shape of wolves and wildcats, but has also led some breeds of cats and dogs to resemble one another, with a convergence toward either long or flat faces. Wild canids (the group of animals that includes dogs, wolves, foxes, and jackals) tend to share a similar elongated skull, while wild felids (the group of animals that includes domestic cats, lions, tigers, and jaguars) exhibit more natural variation.

Domestic breeds of both species now extend further into the extreme ends of this scale, a trend that can be seen in the emergence of cats bred to resemble XL bully dogs.

Domestication has long demonstrated that even distantly related species can end up looking similar, and even suffering from similar conditions, when humans intervene.

Selective breeding has exaggerated some traits in species. Many other human-induced changes can push animals beyond what their bodies can naturally support. For example, some chickens raised for meat carry up to 30 percent of their body weight in breast muscle, often resulting in heart and lung problems.

FEATURES THAT MIMIC THE APPEARANCE OF BABIES

The human preference for flat-faced pets is linked to some of our most basic instincts. Humans are wired to respond to infant characteristics such as round heads, small noses, and large, low-set eyes. These features, exaggerated in many flat-faced breeds of cats and dogs, mimic the appearance of human babies.

Of all species, humans are among the most dependent on maternal care; we are born helpless and dependent on caregivers for our survival. We share this trait with puppies and kittens. In contrast, early-maturing animals can see, hear, stand, and move briefly shortly after birth. Because human babies are so dependent on adult care, evolution has shaped us to be sensitive to signs of vulnerability and need.

These signals, such as babies’ round cheeks and big eyes, are known as social arousers, which trigger a variety of caregiving behaviors in adults, from speaking in higher pitched voices to providing care.

Silver gulls (a type of gull) are an example of this in nonhuman animals. Their young instinctively peck at a red spot on their parents’ beaks, which triggers the adult to bring out food. This red spot acts as a social stimulator, ensuring that the young’s needs are met at the right time. Similarly, domesticated animals are effectively using ancient care mechanisms that evolved for our own lineage.

These traits may give pets an advantage in demanding care and attention from humans, but they come with a price.

The UK government appointed the Animal Welfare Committee to provide independent expert advice on emerging concerns in animal welfare. In their report published in 2024, the committee raised serious concerns about the effects of selective breeding in both cats and dogs.

Reports highlight that breeding for extreme physical characteristics, such as flat faces and exaggerated skull shapes, leads to widespread health problems, including breathing difficulties, neurological conditions and birth complications.

The committee says animals with severe hereditary health problems should no longer be used for breeding and is calling for stricter regulation of breeders. Without these reforms, many popular breeds will continue to suffer from preventable and life-limiting conditions. Selective breeding has shown how easily humans can bend nature to their own preferences, and how easily millions of years of evolutionary separation can be overridden by decades of artificial selection.

By choosing pets that resemble our own babies’ faces, we often unknowingly choose traits that harm those animals. Understanding the forces driving species convergence reminds us that we play a powerful and sometimes dangerous role in shaping it.