Why do dogs look like their owners?

Visit any dog park, and you're bound to see matching pairs of dogs and humans. But do dogs really tend to look like their owners? And, if so, what's responsible for this resemblance? 

"Whilst not a universal phenomenon amongst all owners and dogs, there is some evidence that purebred dogs and owners tend to resemble each other at some level," Katrina Holland, a research officer on the human behavior team at Dogs Trust, an animal welfare charity in the U.K., told Live Science in an email. 

Several studies have found that people can successfully match pictures of purebred dogs with pictures of their owners at levels above random chance. In one study, participants were able to match dogs with their owners regardless of whether they were told to choose the real dog-owner pairs or just choose pairs that looked alike. This finding suggests that it's physical appearance, and not some other element, that people are using to make these judgments.

Certain aspects of physical appearance are more important than others. Facial features, especially the eyes, are more integral to the perception of resemblance than qualities such as size, hairstyle and physical fitness, a different 2015 study found. When a researcher showed participants real and fake dog-owner pairs while masking different parts of the dogs' and owners' facial features, the participants were equally successful at matching when they saw only the eye region as when they saw the full face or the face with the mouth covered. But when they masked the eye region, the participants' success rate dropped to 50-50.

So if it's true that dogs tend to look like their owners, why is this? Do we choose dogs that look like us, or do our dogs start to look more like us over time?

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Research suggests it's probably the former, Holland said.