6 Rules for Touching Humans, Based on Science

Hugs, handshakes, butt pats: Touching among humans is, well, a touchy subject. As kids we were taught that there’s good and bad touches—and it only got more complicated from there. Nobody is immune to the vagaries and complications, either: How politicians touch—from former President George W. Bush's famous Merkel-shoulder-rub gaffe to Michelle Obama's half-embrace of the Queen—is often controversial, and there's seemingly never-ending debate in business circles about hugging vs. handshaking (and let's not even get into single- vs. double-cheek kissing). At the same time, touching is essential to human bonding, stimulating oxytocin and endorphins.

Perhaps science can sort this out? Here are some rules on the subject from research.


For a long time, it was believed that touch was the “simple sense”: that the brain, and specifically the somatosensory cortex, interpreted basic information like temperature and pressure as received by the skin—and that’s it. One 2012 study of heterosexual males showed that the brain processes touch using more cues than just physical sensation. In the study, the subjects received a "sensual caress" from an unseen hand while watching a video clip of either a woman or a man who appeared to be delivering the well-timed touch. In reality, every stroke was delivered by a woman's hand. Looking at fMRIs of the men's brain activity, researchers saw that their somatosensory cortex responded more significantly to what they believed was the woman’s touch than to the man’s. So that “simple” part of the brain wasn’t just interpreting physical cues, but was also accounting for cultural and emotional information. As far as the brain was concerned, those aspects of touch were inseparable from physical stimulation. 


A study published recently in PNAS determined that it’s the closeness of the relationship, rather than frequency of seeing a person, that determined how acceptable intimate touch was—which surprised researchers, until they realized why. Lead author Robin Dunbar, of the Department of Experimental Psychology at Oxford, tells mental_floss that the results make sense when you consider that “what is important in a relationship is how you feel about the person. The frequency of contact is simply the vehicle to achieve that, not the thing itself,” he says.


In a 2006 study [PDF] that involved participants in the United States and Spain, random pairs of strangers were separated, with just a black curtain between them. One was given the task of communicating an emotion by touching the other person’s hand or arm. Researchers found that the people being touched “could decode anger, fear, disgust, love, gratitude, and sympathy via touch at much-better-than-chance levels." Another study by the same researchers found that people could accurately decode distinct emotions by merely watching others communicate by touching each other. In short, touch gave just as much information as tone of voice or facial expression.


Naturally, this is not permission for anyone to touch women more (I’m talking to you, creepy subway guy and inappropriate co-worker), but according to Dunbar’s PNAS study (see #2), women are—in general—both more comfortable being touched and more likely to touch others. This touchiness appears to cement deeper connections: "participants reported feeling stronger emotional bonds with female than male members of their social networks," according to the study.  


The same study also found that the rules of touch don’t vary as much as we think. While his study only looked at European countries, the expected differences between, for example, Finns and Italians—traditionally thought to be on either side of a great European touch divide, with northern cultures hands-off and Mediterranean cultures hands-on—was smaller than anticipated, suggesting the basics of touch are less of a cultural artifact than we might assume. 


Touching others is just fundamentally confusing: “…we are always caught between two things—that we express closeness by more touch and that we try to use touch to express more closeness (when it doesn't exist but we would like it to). So it is always a bit risky, and that is why people get into trouble,” Dunbar tells mental_floss. His best advice for reaching out? “Be careful! Read the signals first!” Perhaps we should update the old school rule: Until you know what's acceptable, keep your hands to yourself. 

AFP, Stringer, Getty Images
Stones, Bones, and Wrecks
The Most Complete Fossil of an Early Human Relative Goes on Display
AFP, Stringer, Getty Images
AFP, Stringer, Getty Images

Twenty years after it was discovered in an African cave, one of the most important fossils in the quest to demystify human evolution is finally on display. As Smithsonian reports, Little Foot, an Australopithecus specimen dating back more than 3 million years, was revealed to the public this month at the Hominin Vault at the University of the Witwatersrand’s Evolutionary Studies Institute in Johannesburg, South Africa.

Paleontologist Ron Clarke discovered the first bone fragments from the fossil in 1994. The pieces came from the remains of a young female’s feet, hence the nickname. Clarke and his team spent years excavating Little Foot bit by bit from the Sterkfontein cave system in South Africa until the bones were fully removed in 2012. The shattered remains had been embedded in a concrete-like material called breccia, making them incredibly tricky to recover. But the sum of the parts is monumental: Little Foot is the most complete Austrolopithecus fossil known to science.

The hominid genus Austrolopithecus played an essential early role in the chain of human evolution. Lucy, another famous hominid fossil, is a member of the same genus, but while Lucy is only 40 percent complete, Little Foot retains 90 percent of her skeleton, including her head. It’s also possible that Little Foot surpasses Lucy in age. Most paleontologists agree that Lucy lived about 3.2 million years ago, while one analysis places Little Foot’s age at 3.67 million years.

Austrolopithecus is believed to have spawned Homo, the genus that would eventually contain our species. The discovery of Lucy and other fossils have led scientists to designate East Africa as the cradle of human evolution, but if Little Foot is really as old as tests suggest, then South Africa may deserve a more prominent point in the timeline.

Following Little Foot’s public debut, the team that’s been studying her plans to release a number of papers exploring the many questions her discovery raises.

[h/t Smithsonian]

Mark Golitko
Stones, Bones, and Wrecks
6000-Year-Old Skull Might Belong to World's Oldest Tsunami Victim
Scientists speak to residents in Aitape.
Scientists speak to residents in Aitape.
Mark Golitko

Tsunamis and other natural disasters have taken a deadly toll on human populations for millennia, and now we may have the oldest example of that truth yet. An international team of anthropologists and environmental researchers recently analyzed a cracked skull that belonged to a person who likely died in a tsunami some 6000 years ago. They detail their find in a new study published in PLOS One.

The partial skull in question, known as the Aitape skull, was found in Papua New Guinea in 1929 during a geological survey by an Australian scientist named Paul Hossfield. It has since been dated to the mid-Holocene epoch, or around 6000 years ago.

For the current study, the scientists returned to the site of the 1929 discovery to sample and analyze the sediment there to find out more about what might have killed the person millennia ago. They had only Hossfield's basic field descriptions to go on, but University of Notre Dame anthropologist Mark Golitko, one of the study’s authors, says that based on those descriptions, they think they were able to sample within 100 yards or so of the skull's original location.

The top of a brown cracked skull against a pink background
Arthur Durband

Based on the grain size, chemical signature, and marine microalgae found within the sediment samples, they were able to determine that around the time that the skull was buried, the area was inundated with water, probably from a tsunami. At that time, the site, located near the present-day town of Aitape, would have been just along the shoreline. Aitape was also the site of a devastating tsunami in 1998, and the Holocene sediments resembled the ones associated with that disaster.

It's possible that the skull was buried before the tsunami hit, and the grave was ripped apart by the waters and the rest of the bones scattered. However, during the powerful 1998 tsunami that killed more than 2100 people in Papua New Guinea, bodies buried in modern cemeteries were not uprooted even as the sediment above them washed away, making it more likely that the ancient skull belonged to someone killed in the disaster.

The new analysis has "made us realize that human populations in this area have been affected by these massive inundations for thousands of years," study co-author James Goff of the University of New South Wales said in a press statement. "Given the evidence we have in hand, we are more convinced than before that this person was either violently killed by a tsunami, or had their grave ripped open by one."

Field Museum anthropologist John Terrell, another co-author of the study, said, "If we are right about how this person had died thousands of years ago, we have dramatic proof that living by the sea isn't always a life of beautiful golden sunsets and great surfing conditions."


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