🍄 We are family. I got all my microbes with me.

The social biome: Let science state for the record, we're giving love in a microbial dose.

Nov 24, 2023

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Hello, we’re Alice and we are always in a state of wander…Humans? We are a walking mountain of bugs. This is a microbial world—and we have a lot to thank our microbes for (we wrote a book, newsletters and a podcast on the prowess of microbes). You and all the systems in your body have evolved, or coevolved, with your microbes. Various parts of the body have very different communities of microbes, yet the distinct microbes in our gut, our oral cavity, and on our skin all turn out to be critical to our microbial fingerprint that can identify the unique you. According to a study by Harvard’s T. H. Chan School of Public Health, our personal microorganisms have distinguishing features that stay with us over time, and our microbiome data may be able to identify us like DNA does in genetic tests.

The Social Gut

Katerina Johnson, PhD, Experimental Psychologist at Oxford University, set out to examine if there was a connection between the composition of the gut bacteria and personality traits such as sociability and neuroticism. And the result could make you and your Instagram followers happy: people with robust social networks were more likely to have a more diverse composition of gut bacteria.

The study collected fecal samples from 655 adults, 71 percent of whom were female and 29 percent male, with an average age of forty-two. The study also involved the participants answering a comprehensive questionnaire that inquired about their behavior, health, lifestyle, and sociodemographic factors. Johnson carried out a set of statistical analysis to help determine the relationship between the composition of the gut bacteria and behavioral traits such as sociability and neuroticism.

This is the first study to find a link between sociability and microbiome diversity in humans and follows on similar findings in primates, which have shown that social interactions can promote gut microbiome diversity. The analysis also revealed that lower microbial diversity was associated with higher levels of stress and anxiety. Seriously, it’s time to get more social. Your gut will thank you.

Eat Your Way to a More Social Microbiome

You are what you digest—and more importantly, what your bacteria digest. People who ate more foods with naturally occurring probiotics or prebiotics had significantly lower levels of anxiety, stress, and neuroticism. However, Johnson didn’t find the same correlation with probiotics or prebiotics in supplement form. Natural sources of probiotics include fermented cheese, sauerkraut, kimchi, and natural sources of prebiotics include bananas, legumes, whole grains, asparagus, onions, and leeks.

Another intriguing finding was that people who had been fed formula as infants had a less diverse gut microbiome. This is the first time this has been investigated in adults, and the results suggest that infant nutrition may have long-term consequences for gut health.

Speaking about the gut—research shows that our gut microbiomes are shaped by the people around us. Researchers at the University of Trento conducted a large study of more than 7,000 people from households around the world to find out which bacterial strains were in their guts and what proportion they shared with others.

Everyone Can See We're Together

People living in the same household share more than just a roof (and the remote control). Housemates—whether family or roomie— tend to have the same microbes colonizing their bodies, and the longer the cohabitation, the more similar these microbiomes become.

Bacterial strains are slight genetic variants of the same bacterial species and are highly individualized, meaning if two people share a strain, it must have been directly transmitted between them. As expected, infants under the age of 1 and their mothers shared the most strains of gut bacteria: about 50 per cent. But by the time children reached the age of 3, they only shared 27 per cent of strains with their mothers and an increasing contribution came from other household members, such as their fathers or siblings.

Gut and Marriage

Here’s something to ponder: your long-standing relationship (marriage to some) can influence your gut microbiota. Analysis of the gut microbiome of spouses and siblings revealed that spouses have more similar microbiota and more bacterial taxa in common than with their siblings. Turns out marriage does have its microbial advantages: married individuals harbor microbial communities of greater diversity and richness relative to those living alone, with the greatest diversity among couples reporting close relationships. One study, for example, found that couples exchange 80 million bacteria on average during a 10-second intimate kiss.

“I jokingly say that your dating app profile should include your microbiome profile,. —Brett Finlay at the University of British Columbia in Canada.

All You Need is Microbial Love

More than part of your family—Fido is part of your microbiome. Our canine family members affect our microbiome. A study at the University of Colorado showed that simply owning a dog had an impact on the sharing of microbes between one person and another living in the same place. Even more interesting is that cohabiting couples who owned dogs had more bacteria in common with each other than couples who didn’t have dogs. The sharing process of their microbiome was in the pets—when one partner strokes a dog, they leave behind bacteria, and when the other partner gives their dog some loves, they pick up their partner’s bacteria.

There are many health benefits to owning a pet, and dogs get a high rating: people who own dogs are happier, less stressed, and even less likely to die of heart disease. But the University of Colorado research begs the question: Could a dog, perhaps, be a type of probiotic for us humans? Could your dog help spread beneficial bacteria?

Living with a dog at an early age is associated with a reduced risk of asthma, eczema, allergies and obesity. In 2017, an analysis of feces from more than 700 infants aged 3 to 4 months in Canada found that those with a dog or cat at home had higher levels of Oscillospira and Ruminococcus bacteria in their guts, both of which are associated with reduced incidence of the likes of asthma and obesity.

Two studies looked at the health benefits of living with a dog, one in children and the other in older people. University of California, San Francisco, scientists suggested that living with a dog starting at infancy may lower a child’s risk of developing asthma and allergies, largely as a result of exposure to what they call “dog-associated house-dust” (also the proverbial “dust bunnies”). The researchers hypothesized that babies and small children need to be exposed to harmless bacteria in order to “train” their developing immune systems, and a dog is a perfect vehicle for that kind of exposure.

One study explored whether dogs could directly improve the health of older individuals. The researchers in Arizona adopted unwanted dogs from the Humane Society, then gave the dogs to people over fifty who either never owned a dog or hadn’t had one for a while. They’re monitoring the physical and mental health of both owner and dog to see if the good bacteria from the dogs is transferred to their new owners, along with other health-boosting benefits. So next time you are feeling a little down, give your dog a big hug and share those good bacteria!

The Genetics of Friendship

Why should bacteria get all the credit? Our friends not only share our behaviors and our interests, they might even share genes in common. Research by scientists at Yale University and the University of California-San Diego revealed that people tend to pick friends who resemble them genetically. In fact, according to the study, close friends are the genetic equivalent of fourth cousins, on average. “This gives us a deeper accounting of the origins of friendship,” explains Nicholas Christakis, professor of sociology and medicine at Yale, and co-author of the study. “Not only do we form ties with people superficially like ourselves, we form ties with people who are like us on a deep genetic level. They’re like our kin, though they’re not.”

The dopamine gene is what we share in common with our friends. One study on twins published from Yale Human Nature Lab found that 46% of the variation in how many friends you have can be explained by your genes. 47% of the variation of the transitivity of friends you have are also based on genes. So if three people are in a room—Jane, Jill and Jackie—where Jane is friends with Jackie depends not just on Jane's genes or on Jackie's genes but on Jill's genes whether Jane and Jackie are friends.

Your Brain Reveals Who Your Friends Are

There’s a neuroscience of friendship. According to a Dartmouth study finding, friends have similar neural responses to real-world stimuli and these similarities can be used to predict who your friends are. The researchers found that you can predict who people are friends with just by looking at how their brains respond to video clips. Friends had the most similar neural activity patterns, followed by friends-of-friends who, in turn, had more similar neural activity than people three degrees removed (friends-of-friends-of-friends).

Friends of Friends of Friends…

Christakis and his long-time research partner James Fowler first introduced the idea of how our social networks shape our lives. In their book Connected, they illustrate how our friends’ friends’ friends affect everything we feel, think and do. That our emotions, behaviors and habits—from smoking to weight gain—can be influenced through our social networks, creating a social contagion. Happiness, for example, is infectious: You are 15 percent more likely to be happy if your direct connection is happy. People who smile on Facebook are generally friends with other smilers.

In a social contagion, it's the connections that matter—not just the people themselves. According to Christakis, "you can take a group of people and connect them one way and they are nice to each other and healthy and innovative and they coordinate their activities or you take the same human capital the same people and arrange the ties in a different topology and they have none of those properties...So it's the ties between people that make the whole greater than the sum of its parts—new properties such as cooperation and violence, health and happiness, innovativeness and sort of economic malaise can emerge because of the connections, because of the ties between people, and not necessarily because of the people themselves."

Emotional Synchrony

Emotional contagion can be triggered by facial expressions, indirect human interactions, and/or by observing other people's behavior in direct and indirect interactions. Emotional contagion can be triggered physiologically or neurologically by synchronizing with the emotional state of others during human interactions. Evidence suggests that emotions can be contagious and cause mind and body arousal toward the interacting party. As a response to emotional contagion, individuals show behavioral, attentional, and emotional synchrony.

Dogs Catch Your Emotions

If you ever catch your dog looking at your face, they are probably recognizing your emotions. Research validates that dogs are able to distinguish emotional facial expressions from neutral expressions, and they can tell happy faces from angry ones—not just in real time, but from photos as well. In fact, some human emotions can even be “contagious” to dogs.

It's a Love Thing

Your dog can sense love too, because they can sense the levels of oxytocin in your brain rise when you are feeling happy to see them. They use their sense of smell to detect this rise in your hormone, oxytocin, which is your happiness hormone. The findings from Japanese researchers suggest we have a bond with our dogs the same way mothers and infants have.

Microbes of Love

Scientists have identified a strain of bacteria that promotes oxytocin and the sense of bonding, altruism and purpose. ALICE spoke with lead researcher Dr. Susan Erdman, principal research scientist and assistant director in the Division of Comparative Medicine at MIT, featured in an ALICE podcast and recent newsletter, “I - I - I'm just a love machine and I won't work for nobody but you...”

Erdman reflected:
“What if our gut bacteria really do guide us to act with a sense of purpose? As it turns out... the molecule behind a meaningful life may well be hypothalamic mastermind oxytocin. Best recognized as the ‘love hormone,’ oxytocin also has roles in childbirth, parenting, and spirituality. Furthermore, oxytocin imparts an otherworldly sense of connectedness with the universe. This transcendental aspect of oxytocin raises the intriguing possibility of a deeply enriched human experience on the other side of microbes. If our ultimate goal is a physically healthy and purposeful life, then our microbial passengers and oxytocin are important partners in our journey.”

Microbes are not just “germs,” they are lyricists. They are the words, the rhyme, and the rhythm for all life on Earth. Being super-social microorganisms, bacteria possess a type of altruism that may have a connection to our very own altruistic behavior.
Give love and thanks to your microbes.

Craving more?

🎧 Microbes and The Love Hormone with Dr. Susan Erdman
🎧 Alice in Futureland podcasts
📘 Alice in Futureland books