Why do people laugh when they get tickled?

For more than a century, people believed that humor and tickling were inextricably intertwined. After all, if tickling didn't help develop good humor, then why would we laugh? Biologist Charles Darwin and physiologist Ewald Hecker posited that humor and tickling are related partly because both require a good mood to be effective (called the Darwin-Hecker hypothesis). Darwin certainly contributed vast amounts of knowledge to science during his lifetime, but he missed the mark with this particular hypothesis. As it turns out, humor and tickling aren't related.

Studies that have sought to test the Darwin-Hecker hypothesis have consistently shown techniques that improve humor, like watching stand-up comedy clips, don't make a person more or less prone to ticklishness. When we laugh during a tickling episode, it's not because we find it funny. Why do we laugh, then?

Evolutionary biologists and neuroscientists have explained (to a point) why we laugh when we're tickled. Simply put, we're showing our submission to an aggressor. The areas of the human body that are typically the most ticklish are the same ones that are the most vulnerable to injury. Humans have evolved to live in social groups and one function of these groups is to pass on knowledge from one generation to another. Through tickling, one person is teaching another to defend himself from attack.

Visualize what you did earlier when that hypothetical finger came at your underarm. Your arms drew close to your side as a defense mechanism. When tickled, a person will also try to fend off the tickler and squirm in an effort to escape. "Tickle attacks [are] the most benign form of human conflict," writes neurologist Robert Provine [source: Provine]. By evoking an involuntary laughter response, the tickle attack remains innocuous, with neither side taking the conflict too seriously.

On the next page, we'll look at some of the more ticklish spots you likely have on your body.