Among cat owners, it’s a common refrain: “Oh no, our cat isn’t an aloof jerk – she’s just like a dog!” That’s usually describing a cat with a taste for human socialization and interaction, and certainly we never hear the opposite phrase. There’s a lot of irony involved, however, because according to researchers at Brown University, several million years ago it was early dogs who evolved to be more like cats – not the other way around.

Lead author Borja Figueirido and his team say climate change at the time was responsible, and not just for the effect it had on prey species – for the first time, researchers believe they’ve demonstrated that climate change itself had a hand in evolution, rather than predators simply adapting to the evolution of their prey.

To understand, first picture the climate of the American Midwest some 40 million years ago. It would have been very warm and wet, covered in dense vegetation. At the time, dogs’ earliest ancestors would have looked more like mongoose, with slender bodies and articulate forelimbs ideal for grabbing and controlling prey in tight quarters. Due to the thick flora, waiting in ambush was an effective strategy.

Figueirido, along with Brown professor of ecology and evolutionary biology Christine Janis, looked at fossils from 32 species of dogs from the aforementioned time period to about two million years ago. By studying the bones of their forelimbs, they observed a clear pattern: As the climate changed and the air became drier, dogs’ forelimbs evolved to take advantage of the more open terrain. With more room to run, the frontal appendages evolved from being flexible and hand-like to sturdier (albeit less articulate) paws – perfect for a cat-like “pursue and pounce” hunting strategy.

Eventually, the middle part of North America dried out such that we got the grassy plains we know today. With fully open terrain, dogs and wolves eventually adopted the long-distance pursuit predation strategy that we see in wolves today. That requires even sturdier paws, and as such modern dogs are unable to pronate their front paws.

While it’s logical to attribute dogs’ evolution to a response to their prey (herbivores grew longer legs to take advantage of more open terrain; dogs responded), the researchers don’t think that’s the case. It wouldn’t have made sense, they say, to evolve more cat-like physiology until the terrain allowed for such a strategy. Instead they believe the climate caused the environment to change, and the earliest dogs took advantage.

“It’s reinforcing the idea that predators may be as directly sensitive to climate and habitat as herbivores,” said Janis. “Although this seems logical, it hadn’t been demonstrated before.”