When rock band R.E.M. belted out "Everybody hurts sometimes," they weren't singing about backaches or sprained ankles. They were, of course, referring to the intense pain our emotions can cause — like the pang of losing a cherished friend or the heaviness in your chest after a breakup. So why do we experience rejection and loss as literal heartache?

The short answer: It helps us survive.

Many psychologists think the experience of emotional pain "piggybacked" onto the already existing physical pain system in the brains of our early ancestors, said Ethan Kross, a professor of psychology at the University of Michigan and first author of the 2011 PNAS study.

The pain you feel after a fight with a close friend is quite real, Kross told Live Science, but it's not exactly the same as physical pain. "Anyone who has ever been rejected on one occasion and punched in the nose on another can tell you that these experiences are, of course, different," he said. We see that reflected in fMRI studies. The parts of the brain activated by these two different experiences have some overlap, but they're not identical.

Read the full article at Live Science.