Religious texts and folk traditions have claimed for millennia that two people in love transform into a new being. The ancient Greeks believed that human bodies were originally connected in pairs, and that these couples rolled around as complete wheels; Zeus thought that these double-people were too perfect, so he separated them, and courtship and love are our attempts to rejoin our once-conjoined partners. The Book of Genesis states that a husband and wife become “one flesh.” A Japanese tale tells of two lovers who intertwine so tightly that they become a single sea snake and slither out into the ocean. The list goes on.

Now, neuroscientists have confirmed the truth behind these traditional stories. In the last decade, two strands of research have emerged that, when imagined together, provide clinical proof that two people in love are no longer separate organisms: a niche group of neurobiologists have shown that the hearts, brains, and organs of couples synchronize their activity; meanwhile, a global team of neuroimaging specialists have presented a statistical description of life that gives said synchronizations of couples a new meaning. And while no study volunteers have yet transformed into a sea snake and terrorized a lab, the actual discoveries are no less dramatic.

In a time when the traditions that once defined the responsibilities and possibilities of love have mostly broken down, this new love-science—considered alongside the ancient stories it echoes—has the potential to create new foundations for loving relationships. The key question: If my lover and I really are one flesh, what new things can we achieve? Which limits can we overcome when we stop thinking of ourselves as separate individuals? How can my relationship reach that combined perfection Zeus feared so terribly? 

Dearest Dyad

In 2013, UCLA scientists Emilio Farrer and Jonathan Helm wrote in Science Direct, “Heart rate and respiration of couples can be represented as dynamical systems.” Despite the jargon—the paper was titled “Dynamical systems modeling of physiological coregulation in dyadic interactions”—this sentence belies some of its revolutionary explosiveness: the vital rhythms of couples regulate each other, so that when one’s heart accelerates, the other’s follows.

In the same issue of the same journal, a group of scientists led by UCLA professor Theodore Robles found that girlfriends more anxious about their attachment to their boyfriends recovered more quickly from minor skin injuries than those less anxious. In a demonstration of the tight relationship between seemingly separate biological systems, they shored up physical barriers to compensate for wavering minds. Meanwhile, the girlfriends who outright avoided deep attachments recovered more slowly.

These two papers, when considered together, mean that couples can form a bond so tight that it extends through levels of unconscious physical function, from heart rates to breathing to healing from injury. A recent EEG-imaging study published in NeuroImage journal has also confirmed that particularly close couples’ brain rhythms synchronize. The people you love can influence every aspect of your physical functioning, from brain to heart to skin and everything in between. 

Snuggies and Markov Blankets

Imagine: It’s a lazy Sunday. Lukewarm skies of platinum clouds, tiny trickles of rain, thin cowbird calls carry from the willow outside your bedroom window. You and your sweetheart have laid down for a nap after a heavy lunch. You just moved into a new apartment, and you’re broke, so you lie upon a bare mattress, and, instead of a sheet, you share an extra-large Snuggie blanket. You lie chest-to-back, and each of you feels the other’s pulse. You move minutely as your lover’s ribs rise and fall with heavy breath.

You already know that your hearts and lungs influence each other and that your brain waves synchronize, so that it will be harder for one of you to fall asleep if the other is wired. But according to the work of Karl Friston, a neuroimaging specialist at University College London, you and your lover have enacted a more radical, even world-shaking transformation. Your extra-large Snuggie is not just a sign that you’re broke. It is the skin of a new organism.

Friston, in a 2010 paper titled “The free-energy principle: a unified brain theory?”, argues that all the actions of the nervous system—from basic senses up to complex thoughts—boil down to an attempt to minimize “free energy.” This free energy, he says, is essentially the same as surprise. The senses work to take in the most accurate data they can, while the brain tries to turn that data into an accurate model of the world. When some part of that model looks threateningly unpredictable—you bump into a quick-tempered stranger while walking or your blood pressure suddenly falls—your brain conjures up a series of actions to minimize that unpredictability. For example, if you’re walking across a street, and you see a car coming, you’ll sprint to the opposite sidewalk or jump back to the curb to avoid the unpredictable threat posed by a collision. 

[Prions Are Going to End the World]

Over the past decade, Friston has worked with an international team from Amsterdam to Australia to turn this free-energy principle into a new universal theory of life. In 2018, this group published a paper in the Journal of the Royal Society Interface, “The Markov blankets of life: autonomy, active interference and the free energy principle,” a gigantic tour de force of neuroscience. This paper turns your shared Snuggie into skin and upends commonsense theories of life.

According to Friston’s team, a Markov blanket is a two-way barrier between the inside and outside of a life. This barrier is a statistical model that describes the ways information enters and leaves the space taken up by a life. Thus, one half of the Markov blanket is made of “sensory states,” or the senses—sight, smell, hearing, and so on—that pull information from the world into your body. The Markov blanket’s second half consists of “active states,” the actions you take that attempt to reduce the potential surprises presented by the outside world. Anything that performs both these actions—sensing things outside a barrier and acting to affect those things—can therefore be called “living.” These Markov blankets are constructed like a Russian nesting doll: every cell has one, in the form of the cell wall or membrane, and every organ has one, and every full organism is surrounded by another. (The technology theorist Benjamin Bratton claims that this nesting doll keeps adding layers up to planetary scale, but that's a conversation for another essay.)

In your case, though, lying inside the Snuggie with your lover, where is this final Markov blanket? Your skin is one such barrier: you can feel your lover’s warmth, see his tousled hair, smell her sweet scent. But if your vital rhythms and brain waves regulate each other in a back-and-forth system, your skin isn’t the last barrier. In this case, the final Markov blanket is the Snuggie.

Imagine: A bird crashes into the window. You are asleep. Your lover is awake. Her eyes dart to the sound, her heart pounds, she takes a sharp breath. Careful not to wake you, she resisted the urge to jump in surprise; but your heart has accelerated with hers, and your breaths come more quickly. You awaken, and though you did not hear the bird’s collision with the glass, you immediately ask, “What’s wrong?” Your own conscious sensory experience cannot have prompted this question. Heart to heart, breath to breath, you and your lover have created a new organism at a new scale. 

After all this time, neuroscience has caught up to the Bible when it says, in Genesis 2:24, that a couple becomes “one flesh.”

Common-Law Marriage

In February of 2021, a team of scientists led by Amir Djalovski built upon studies of synchronization between couples to demonstrate a range of other types of mental entanglement. Separating their subjects into three groups of pairs—couples, best friends, and total strangers—the scientists recorded their brain rhythms while each pair drew shapes with an Etch-a-Sketch then talked about traumatic experiences.

Djalovski and his cohort then compared the pairs’ EEG scans and charted the similarities and differences in their Etch-a-Sketch drawings. The couples’ results fell perfectly in line with earlier studies: they were the most synchronized on all levels of brain activity. But Djalovski and company also found that the brains of best friends and even strangers synchronized to some degree. These synchronizations fell into a hierarchy according to the relationship between each pair. The brain rhythms of couples came closest to each other, best friends synchronized a bit less, and strangers still less. In any case, however, this study demonstrates a crucial component of social interaction: though love produces the strongest connection, the sheer fact that you are near someone causes your brains and bodies to begin to mimic each other.

The philosopher Georges Bataille came to this same idea by sheer intuition almost eighty years ago in his book On Nietzsche, which he wrote while isolated in his apartment during the Nazi occupation of Paris. Not tied to any desire for scientific precision, he expanded the idea to its most extreme possible conclusion. He asked, terrified, “Can I consider anything human a stranger to myself?”

Laws are written to regulate singular people. If I murder someone, and my lover knows nothing about it but helps me by loving me, I will be charged with murder, and she will not stand trial for anything. However, if law were forced to acknowledge that my murder was not only my murder, but a result of the combined physiological and psychological influences of everyone I love, how would I—or anyone—be proclaimed guilty? The court would have to track down everyone I had hugged in the weeks or months before the murder and determine what effect they had on my biology that may have influenced my action. Then it would have to track down their loved ones. In the end, whole nations might receive indictments.

Studies show that the biological synchrony of couples can be used to predict the states of those couples years later. What can law do, if every defendant is a composite of all the people with whom he has interacted in the past few years? The legal system either dissolves, or it is forced to assume a theory of individual action that is biologically false. Medicine faces similar problems, along with psychology, economics, and every field that considers humans as separate individuals.

[The Countere Guide to Spotting NPCs]

Suddenly it appears as though each action projects onto the experiences of thousands, even millions of other lives, endowing each person with a radical responsibility that reaches far past what can be consciously understood. Imagine: I am sitting on a bus with heart-fluttering jitters before a competition. It is a long ride, and I strike up a conversation with the woman next to me, who unwittingly takes on some of my jitters. She passes this small cardiac stress to a coworker who passes it to his daughter who passes my pre-competition nervousness to a classmate who has come to school with a gun. Have I tipped him over the edge and, in part, caused a school shooting? In such a light, even wider moral questions about countrywide problems take on a nuance unmentionable in ethical or political conversation. 

For similar reasons, the responsibilities of love open up into a new, expanded range when the lovers are understood as “one flesh,” a range that extends far beyond the contractual “in sickness and in health” of formal marriage. If your wife suffers from high blood pressure or a pulse too fast, it is your responsibility to get into great physical shape so that your heart can help regulate hers. If your husband is chronically anxious, you can help him by becoming steadfast and confident: your brain rhythms will downregulate his. Because the basic science that enables such claims has developed so recently, no one has studied these kinds of treatments directly. 

However, similar implications can be found indirectly through other research. For instance, we have known for quite some time that couples have far longer life expectancies—more than a decade longer—than single folks. This difference disappears, however, if one lover dies; the widow or widower’s life expectancy drops immediately. Given that the leading cause of death, at least in the United States, is heart disease, and that couples’ hearts regulate each other as a paired system, it is possible that the death of a longtime lover has similar effects to the removal of a medically inserted pacemaker. 

Once more, these claims have not been directly researched, at least not yet. But if the relatively simple deductions that led to them are correct, supporting your lover becomes not only a generous act, but a responsibility to improve in the domains in which they struggle.

Along with these responsibilities arrives a host of world-opening possibilities. I have heard tons of times that shared goals are the key to a strong relationship. But now the same truism works in reverse: a strong relationship is the key to achieving shared goals. Imagine: my girlfriend and I each dream of being great writers. The worst thing we can do, then, is to fall into the old genius-artist trope of isolated living and romantic inconstancy. The closer we become, the more each of our successes will improve the abilities of the other, from the most basic physiological levels upward. Many have said it, but your life partner is literally your most important life decision. 

The ancient Greek term aristeuein denoted the ideal that one should become absolutely superior in everything one did. The theory of love as a literal, physical fusion, developed in ancient texts and recently rediscovered by neuroscientists around the world, enables a new level of aristeuein, one which works with biological fusions to make superhumans of the most tightly connected lovers. 

Above and beyond the contractual legalisms of modern marriage and the coldness of hook-up culture, this type of love acts according to a common law—traced through spiritual traditions to neuroscientific proof—which actually creates a new type of composite life from formerly separate human bodies. This biologically explosive love has the potential to upend the way we think about minds and bodies. Thus I imagine that, when Plato read to the ancient Greeks of the original humans, couples attached to each other as perfect circles, and when he told them how Zeus separated these circles because he was afraid of their perfection, someone must have asked, “What was life like for these better humans?” And I know now that this question demands neither a mythological nor a historical answer, but a futuristic one.

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