We shed tears when in pain, but what purpose does crying have?
A scientist now proposes a new theory for why crying evolved — tears can act as handicaps to show you have lowered your defenses.
"Crying is a highly evolved behavior," said researcher Oren Hasson, an evolutionary biologist at Tel Aviv University in Israel. "My analysis suggests that by blurring vision, tears lower defenses and reliably function as signals of submission, a cry for help, and even in a mutual display of attachment and as a group display of cohesion."
The shedding of tears due to emotions is unique to humans. In the past, researchers suggested that crying helps carry stressful chemicals away from the body, or that it simply makes us feel better, or that it lets babies signal health problems.
Now Hasson points out that when tears blur vision, they could readily handicap aggressive behavior. As such, tears reliably signal vulnerability, a strategy that can emotionally bind others closer to you.
Hasson suggested the use of tears could be to build and strengthen personal relationships. For instance, "you can show that you are submissive to an attacker, and therefore potentially elicit mercy from an enemy, or you could attract sympathy from others, and perhaps gain their strategic assistance," he told LiveScience.
Also, by sharing tears with others, "if you can get a mutual display of lowered defenses, that means we can bond, that shows that we are really friends who share the same emotions," Hasson said. "This is strictly human."
"Of course," Hasson added, "the efficacy of this evolutionary behavior always depends on who you're with when you cry those buckets of tears, and it probably won't be effective in places, like at work, when emotions should be hidden."
This new concept from Hasson "offers the most plausible hypothesis about the evolved function of tears and crying," said evolutionary psychologist David Buss at the University of Texas at Austin, who did not participate in this study. "Others have speculated about possible function of tears, but the notion that they operate through handicapping is highly original."
Hasson detailed his research in the journal Evolutionary Psychology.
Live Science newsletter
Stay up to date on the latest science news by signing up for our Essentials newsletter.