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Loneliness, it turns out, is much more than a feeling. The condition can shave years off your life and may even be genetic. But why? Why, God, why?

Researchers from the University of Leuven, University of Chicago and VU University Amsterdam set out to answer this question and more through a series of studies on the evolutionary and biological origins of loneliness. Their findings were just published in Perspectives on Psychological Science. Here's what they revealed.

We evolved to feel lonely to help us survive.

Aside from those rare occasions when wallowing is actually kind of enjoyable, loneliness feels pretty terrible. There's a reason for that: The researchers hypothesize that humans evolved to avoid loneliness as a survival mechanism. Humans are social creatures by nature, and previous research has shown that we live longer when surrounded by strong support systems. Conversely, loneliness triggers our bodies to activate our stress response systems—the sadness and pain associated with being alone is a signal to go out and connect with people.

Loneliness "indicates that important social connections are at risk or absent and acts as a motivating force to reconnect with others," the researchers explain. "As such, loneliness has played an important role in the evolution of the human species, given that reconnecting with others increases one’s chances of survival and opportunities to pass on one’s genes to the next generation."

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Loneliness can be inherited.

If your mom and your mom's mom and basically everyone in your family tends to suffer from feelings of loneliness, chances are you will, too. The researchers believe that loneliness is an inheritable trait. By analyzing several studies  involving twins and relatives—including one study that looked at adopted family members—the researchers concluded that the heritability of loneliness is just below fifty percent, which they considered "significant."

Specific genes may code for loneliness.

The obvious step after realizing loneliness can be inherited is to find genetic markers that code for it, called alleles. Researchers can take two approaches to isolating these alleles. First, they can look at "candidate-gene studies," in which specific gene groups are targeted based on the systems they control. When looking for genes linked to loneliness, specifically, researchers concentrated on systems related to neurotransmitters such as dopamine, serotonin, and oxytocin—chemicals that play a role in love, connection, happiness, and pair-bonding.

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Through these studies, researchers found that individuals with a gene called OXTR—which codes for oxytocin reception—are more social, trusting, and sensitive to social cues. And sure enough, they discovered that young girls and pregnant women who had this gene were less lonely. Thus, this gene is a good candidate to continue exploring.

Another strong candidate for a loneliness gene is the serotonin transporter gene (SLC6A4). According to the researchers, the short allele of this particular gene is linked to less efficient dampening of negative emotions. "This less efficient dampening, in turn, can be linked to hypervigilance to social threat, which is a key characteristic of lonely people," explain the researchers.

The second method used to discover genetic markers is to look at "genome-wide association studies" (GWAS), which analyze large databases to see if patterns related to a particular trait emerge. So far no GWAS studies have been done specifically for loneliness, however the method has been used to study neuroticism and depression, which could lead to breakthroughs in locating loneliness alleles.

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Environment still plays a role.

Of course, our genes don't determine everything. Researchers found that even people who might be genetically predisposed to loneliness were less likely to express the trait if they were surrounded by strong social networks.

For example, when studying people with the serotonin transporter gene mentioned above, the researchers found that those who "experience a low level of social support clearly feel more lonely than do carriers of that same allele who experience a high level of social support." In other words, nurture still matters.

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Loneliness is associated with weaker immune systems.

When looking for patterns in gene expression, the researchers discovered a link between loneliness and the body's ability to defend itself. In one very small study that compared lonely and non-lonely older adults, they identified 78 genes that were overly expressed in lonely participants and 131 genes that were overly expressed in non-lonely participants. Many of these genes played a large role in biological functions—including immune response.

"These results help illuminate why lonely people show heightened vulnerability to cardiovascular diseases (which are thought to emerge through excessive nonspecific immune activity) and impaired reactions to viral infections (which are thought to be linked to insufficient specific immune activity)," explained the researchers in the paper.

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The expression of these genes may also explain why non-lonely cancer patients tend to live longer than lonely patients: "The fact that expression of loneliness-associated genes proved related to survival time in cancer patients could provide a glimpse into the mechanism underlying the loneliness-mortality link."

What does it all mean?

Based on evolutionary and genetic theories, the researchers believe that loneliness could be a trait that has been passed on as a means of human survival. Feeling lonely—and the stress response it triggers—may be a negative consequence created as a way to spur humans to connect with each other. And finally, some individuals may be more prone to loneliness than others, which could have major effects on their lifespan, if the right support networks are never established.

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Anyone want to grab a few drinks later and play board games and bond over our favorite music?

Taryn Hillin is Fusion's love and sex writer, with a large focus on the science of relationships. She also loves dogs, Bourbon barrel-aged beers and popcorn — not necessarily in that order.