Why We Like to Have Our Backs Scratched

Itch, Scratch, and the Origins of Social Touch

Your skin is essentially a body envelope. It keeps your vital fluids in and protects your heart, lungs, and other viscera from bacteria and dehydration. It’s also the primary medium through which we bond with other people.

This bonding comes in a variety of flavors. We can hold hands, high-five, kiss, cuddle, have sex. But also link arms, play with each others hair, and—sometimes to the point of annoyance—pop each other’s pimples. If there’s an objective fact to be stated about the nature of this universe, it’s that back scratching is the best of these practices.

Back scratching belongs to a subset of bonding behaviors called allogrooming. Allogrooming (allo meaning “other” and grooming meaning “grooming”) didn’t originate for bonding, though. Instead, it evolved as a way to satiate each others grooming needs. Only later did it develop this ability to fortify social bonds.

This miraculous transition was bumpy. It grew from itchy pimples, ugly parasites, and dastardly dead skin. From these cruel curses emerged the shiny and delectable practice it is today. This is the story of that transition.

It Started With An Itch

Certain places on the body are difficult to reach. In primates, these are the head, neck, and back. Because these places are difficult to reach, we would need the help of friends, loved ones, or nearby sticks to deal with them. Friends and loved ones were probably more helpful.

These places would itch for a number of reasons. Lice, for instance, evolved to avoid host grooming and thus focus themselves to these difficult to reach locations. They began an arms race, if you will, between the places we could reach them and the location of their “microhabitat” on the body. Those that survived moved far from reach. Those that didn’t were promptly plucked.

Today we’re not so plagued by lice. We have the acquisition of fire, clothing, and shelter to thank for this. These powerful accoutrements rendered fur more of a flea-ridden nuisance than temperature-regulating asset. Those who dedicated their physiological resources to other things, then, were better off. And so, our fur grew thin, fair, and (mostly) lice-free in response.