Tiny Terror: Ancient Wolves Had Gene Mutation That Makes Dogs Small

Small dogs are not simply the product of domestication and breeding as previously thought. According to a new study, ancient wolves already had a gene mutation for smaller size. (Matt Cardy/Getty Images)

The smallest dogs, such as Chihuahuas and Pomeranians, long thought to be the product of domestication, share a body-size gene with ancient wolves.

A new study published in the journal Current Biology suggests that wolves living more than 50,000 years had a mutation in a gene regulating growth hormones that ultimately resulted in small dogs. This was long before humans began keeping dogs as pets.