If you've ever watched a video of a dog being reunited with its owner, you know how much it can pull on the heartstrings. Sometimes the human owners start crying because they're overcome with emotions, but what if the dogs did the same thing?
A new study says that dogs produce more tears when reunited with their owners compared to when they reunite with familiar humans who are not their owners.
The study was published in Current Biology Magazine last week and challenges the long-held notion that humans are the only creatures that are capable of producing tears as an emotional response.
Researchers used what's known as the Schirmer tear test to measure the dogs' tear volume before and after the reunions. The test is typically used to measure whether an animal or person is producing enough tears to keep their eyes moist.
Small pieces of filter paper are placed inside the lower eyelid. The paper absorbs the tears and then the volume is measured.
For the experiment, the tear volume was measured in the dog's home environment with their owners present and again shortly after the dog and owner were reunited after being apart for five to seven hours.
The researchers also compared tear volume amounts when the dogs were reunited with people they were familiar with, but who were not their owners.
"Dogs secreted larger tear volumes during reunions with their owners than with familiar non-owners, and tear volume during reunion with the owner was significantly greater than the baseline tear volume," the study said.
But not everyone in the science community is convinced. Jessica Meekins is an associate professor of veterinary ophthalmology at Kansas State University. She said her skepticism stems from the way tear production fluctuates in individual animals and species.
"In veterinary ophthalmology, we typically have a cutoff for what we would consider excessive tearing. And to me, that objective number would be a good launching off point for researchers like this to kind of establish [what is] truly significant," she said.
Analyzing the composition of the tears for an emotional trigger, Meekins said, including the hormones, electrolytes, proteins and more would be an interesting addition to a future study.
"It would be interesting to know, rather than just the volume component, whether those tears contain similar molecules to what's been identified in people in certain studies and in trying to investigate why we cry," Meekins said.
But whether you believe the results of the new study or remain skeptical, there is one thing everyone can agree on: all dogs are good dogs.
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