Growing up in the 1990s meant my parents owned a handheld camcorder and tried to capture even the most banal moments of my and my brother’s youth on tape. A few years ago, I found a dusty box of these VHS tapes and popped one of them in an equally dusty—but still functional—VCR player. One scene I remember watching in particular is of me tickling my younger brother non-stop. He was at once laughing and swatting at me with his chubby hands. As the tickling perpetrator, I was also laughing.

The first thing I thought to myself was how obnoxious I had been. The second thing that came to mind was how tickling is a pretty strange thing to do. Could there be a reason why we engage in this activity? Why do adults tickle young children? Why do we laugh in response? Could there be an evolutionary advantage to tickling?

A friend recently said to me, “Whenever I meet someone who isn’t ticklish, it’s like they don’t have a soul.” But even if we laugh when tickled, some theorists think that the laughter tickling elicits is too complicated to be viewed as just a simple reflex. And just because we laugh doesn’t mean tickling is necessarily a benign deed: Medieval warriors sometimes tortured victims by tickling them to death.

The fact that we laugh when tickled is an interesting conundrum. It’s unclear whether this laughter is the same as the laughter elicited from reacting to a funny situation. Some researchers believe that making children laugh—via tickling —can aid in their development of humor. But this isn’t conclusive, argues Christine R. Harris, a psychologist at University of San Diego.

Perhaps, too, there’s a reason why adults tickle children. Tickling could be a way to bond: the child’s reaction to being tickled would cause the caregiver to also crack a smile. Harris explains how this reciprocal smiling and laughter could produce positive social interactions.

Some other researchers believe tickling could be evolutionary advantageous since our most ticklish spots are also areas of the body involved in arm-to-arm combat. In other words, sensitivity in such areas would motivate people to protect them. But there’s a caveat to this theory: hands and fingers, often used during fighting, are among the least ticklish points on the body.

In her piece for American Scientist, Harris proposes a third idea: the person being tickled often exhibits defensive movements—like my brother did in those old tapes—but is also simultaneously laughing, which suggests they are having fun. Perhaps disconnecting the physical discomfort of being tickled by laughing is an adaptive behavior in it of itself. This disconnect could aid in the child developing combat skills that might be advantageous down the line.

Overall, why we tickle others and why we laugh when tickled presents a swath of interesting questions. But, as Harris writes, “Trying to unearth the evolutionary basis for the peculiarities of psychology and physiology is a notoriously treacherous enterprise.”