The Physical Foundations of Friendship

It’s no secret that I worry about what the unintended consequences might be for us as we increasingly substitute a digital world for a physical one. What might happen to our society as we spend less time face-to-face with people and more time face-to-face with a screen?

Take friendship, for example. I have written before about how Facebook friends and real friends are not the same thing. A lot of this has to do with the mental work required to maintain a true friendship. This cognitive requirement led British anthropologist Robin Dunbar to come up with something called Dunbar’s Number – a rough rule-of-thumb that says we can’t really maintain a network of more than 150 friends, give or take a few.

Before you say, “I have way more friends on Facebook than that,” realize that I don’t care what your Facebook Friend count is. Mine numbers at least 3 times more than Dunbar’s 150 limit. But they are not all true friends. Many are just the result of me clicking a link on my laptop. It’s quick, it’s easy, and there is absolutely no requirement to put any skin in the game. Once clicked, I don’t have to do anything to maintain these friendships. They are just part of a digital tally that persists until I might click again, “unfriending” them. Nowhere is the ongoing physical friction that demands the maintenance required to keep a true friendship from slipping into entropy.

So I was wondering – what is that magical physical and mental alchemy that causes us to become friends with someone in the first place? When we share physical space with another human, what is the spark that causes us to want to get to know them better? Or – on the flip side – what are the red flags that cause us to head for the other end of the room to avoid talking to them? Fortunately, there is some science that has addressed those questions.

We become friends because of something in sociology call homophily – being like each other. In today’s world, that leads to some unfortunate social consequences, but in our evolutionary environment, it made sense. It has to do with kinship ties and what ethologist Richard Dawkins called The Selfish Gene. We want family to survive to pass on our genes. The best way to motivate us to protect others is to have an emotional bond to them. And it just so happens that family members tend to look somewhat alike. So we like – or love – others who are like us.

If we tie in the impact of geography over our history, we start to understand why this is so. Geography that restricted travel and led to inbreeding generally dictated a certain degree of genetic “sameness” in our tribe. It was a quick way to sort in-groups from out-groups. And in a bloodier, less politically correct world, this was a matter of survival.

But this geographic connection works both ways. Geographic restrictions lead to homophily, but repeated exposure to the same people also increases the odds that you’ll like them. In psychology, this is called mere-exposure effect.

In these two ways, the limitations of a physical world has a deep, deep impact on the nature of friendship. But let’s focus on the first for a moment. 

It appears we have built-in “friend detectors” that can actually sense genetic similarities. In a rather fascinating study, Nicholas Christakis and James Fowler found that friends are so alike genetically, they could actually be family. If you drill down to the individual building blocks of a gene at the nucleotide level, your friends are as alike genetically to you as your fourth cousin. As Christakis and Fowler say in their study, “friends may be a kind of ‘functional kin’.”

This shows how deeply friendships bonds are hardwired into us. Of course, this doesn’t happen equally across all genes. Evolution is nothing if not practical. For example, Christakis and Fowler found that specific systems do stay “heterophilic” (not alike) – such as our immune system. This makes sense. If you have a group of people who stay in close proximity to each other, it’s going to remain more resistant to epidemics if there is some variety in what they’re individually immune to. If everyone had exactly the same immunity profile, the group would be highly resistant to some bugs and completely vulnerable to others. It would be putting all your disease prevention eggs in one basket.

But in another example of extreme genetic practicality, how similar we smell to our friends can be determined genetically.  Think about it. Would you rather be close to people who generally smell the same, or those that smell different? It seems a little silly in today’s world of private homes and extreme hygiene, but when you’re sharing very close living quarters with others and there’s no such thing as showers and baths, how everyone smells becomes extremely important.

Christakis and Fowler found that our olfactory sensibilities tend to trend to the homophilic side between friends. In other words, the people we like smell alike. And this is important because of something called olfactory fatigue. We use smell as a difference detector. It warns us when something is not right. And our nose starts to ignore smells it gets used to, even offensive ones. It’s why you can’t smell your own typical body odor. Or, in another even less elegant example, it’s why your farts don’t stink as much as others. 

Given all this, it would make sense that if you had to spend time close to others, you would pick people who smelled like you. Your nose would automatically be less sensitive to their own smells. And that’s exactly what a new study from the Weizmann Institute of Science found. In the study, the scent signatures of complete strangers were sampled using an electronic sniffer called an eNose. Then the strangers were asked to engage in nonverbal social interactions in pairs. After, they were asked to rate each interaction based on how likely they would be to become friends with the person. The result? Based on their smells alone, the researchers were able to predict with 71% accuracy who would become friends.

The foundations of friendship run deep – down to the genetic building blocks that make us who we are. These foundations were built in a physical world over millions of years. They engage senses that evolved to help us experience that physical world. Those foundations are not going to disappear in the next decade or two, no matter how addictive Facebook or TikTok becomes. We can continue to layer technology over these foundations, but to deny them it to ignore human nature.

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