Domestic dogs come in more sizes than any other mammal species. Now, researchers say a genetic mutation that emerged in wolves before they were domesticated is responsible.

On appearances alone, it may be hard to believe dogs like fluffy Pomeranians or spritely Chihuahuas really are descended from wolves.

But new research both illuminates and solidifies this relationship, while providing a new explanation as to why owners are even able to pick teacup poodles and short-snouted Shih Tzus out of the pack.

Domestic dogs come in more sizes than any other mammal species on Earth. This is a result of human preference and selective breeding — but this wide range of sizes is foundationally possible because of a newly discovered genetic mutation.

This mutation corresponds to small body size and it emerged in wolves before they were domesticated.

Source: Yes, those tiny dogs descended from wolves