Feeling sick and stuffy-headed? Don't go to work.
The research, which first appeared in October at the journal PLOS Biology, suggests that the physical feeling of sickness may be an evolutionary adaptation to alert us that it's time to isolate ourselves from the herd.
The paper's authors list a series of symptoms that all seem geared toward separating the individual from their larger social group, including losing your appetite (which creates a smaller chance that you'll contaminate the group's food), fatigue and weakness (making you less likely to get out of bed and interact with the community), and lack of interest in sexual contact (which speaks for itself).
These behavioral symptoms that accompany sickness don't do anything to help the individual's chances of survival and reproduction, the researchers argue. So why have they persisted?
The researchers posit that "sickness behavior" is an evolutionary adaptation meant to limit the spread of disease. While the individual may not survive the illness, by isolating himself from the social group, he or she will reduce the overall infection rate within the community.
It's worth noting that we aren't the only species to do this: Bees also exhibit "sickness behavior" when they're ill, abandoning the hive to die elsewhere.
"We think it's an altruistic behavior -- you do it not for yourself but for your relatives," Dr. Guy Shakhar, an immunologist at the Weizmann Institute and the paper's co-author, told The Huffington Post.
While most infections aren't a question of life or death for modern humans, this theory does still have an application in today's world, where it has become routine to cover up the symptoms of sickness with drugs.
"We tend to still go to work when we're sick, or give our children some Tylenol and send them off to school, so they get over their sickness behaviors and go on to infect somebody else," Shakhar said. "I'm not saying to stop taking the anti-inflammatory drugs when you're sick, but be aware that just because the sickness behaviors are gone it doesn't mean you're not infectious."
That's right: If you have a cold, evolution is telling you not to go to work. You can always tell your boss that staying home is the way our human ancestors intended it.