Scientists take a peek behind those sad puppy dog eyes

FILE - This Feb. 18, 2014 shows Lexy, a therapy dog at Fort Bragg, N.C. A study released on Monday, June 17, 2019 suggests that over thousands of year...

FILE - This Feb. 18, 2014 shows Lexy, a therapy dog at Fort Bragg, N.C. A study released on Monday, June 17, 2019 suggests that over thousands of year...

FILE - In this Monday, May 13, 2019 file photo, a female red wolf emerges from her den sheltering newborn pups at the Museum of Life and Science in Du...

FILE - In this Monday, May 13, 2019 file photo, a female red wolf emerges from her den sheltering newborn pups at the Museum of Life and Science in Du...

FILE - In this Wednesday, Jan. 30, 2013, file photo, a Labrador retriever named Shayna attends a news conference at the American Kennel Club in New Yo...

FILE - In this Wednesday, Jan. 30, 2013, file photo, a Labrador retriever named Shayna attends a news conference at the American Kennel Club in New Yo...

This diagram provided by Tim Smith in June 2019 shows a comparison between dog and wolf facial muscles. A study released on Monday, June 17, 2019 sugg...

This diagram provided by Tim Smith in June 2019 shows a comparison between dog and wolf facial muscles. A study released on Monday, June 17, 2019 sugg...

NEW YORK (AP) — Scientists say they've figured out why dogs can make those sad puppy dog eyes at you. It turns out, it's because of us.

Thousands of years of living with people encouraged dogs to develop a muscle that lets them raise their eyebrows so they look more babylike. And people may have unwittingly preferred pups that could make that expression.

Researchers suggested this in a study released Monday by the Proceedings of the National Academy of Sciences.

They showed that this muscle is virtually absent in wolves, the ancestors of dogs.

The researchers believe dogs used this eye muscle to communicate with humans, possibly goading people to feed or care for them — or at least take them out to play.