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How the Human Brain Is Wired for Romance

Humans are evolutionarily drawn to beauty. How do such complex experiences emerge from a collection of atoms and molecules?

Couple enjoying a full moon over the Reservoir in Central Park in New York City,

Recently, I found myself in the office of the neuroscientist Robert Desimone, the director of the McGovern Institute for Brain Research at MIT, discussing what it takes to know that two people are going to fall in love.

We sat next to a large glass cabinet containing the historical artifacts and curiosities of brain science: a wooden box bristling with electrodes and wires used for inducing electrical currents and shocks to the brain; a brain-wave “synchronizer” with a flashing vacuum tube; and a frightening metal spike, dating back to the 1940s, to be hammered into the brain to perform lobotomies.

I asked Desimone if he thought that brain scientists of the future might be able to predict whether two people would someday fall in love, given a full readout of their neurons. Desimone replied with a boyish grin: “I’m a reductionist. So yes,” he told me. He allowed that, at the moment, our models are only probabilistic. They would say, “There’s a 70 percent probability you’ll fall in love with Mary, and a 40 percent chance you’ll fall in love with Alice.”

But, according to Desimone, the predictive probabilities in the future will inch up toward 100 percent. I’m a scientist myself, but I find it a bit unsettling that a brain scientist or computer might accurately predict whom I’ll fall in love with. At the same time, I admire the spectacular progress of science in understanding human beings and where we fit in the grand scheme of things.

The Transcendent Brain: Spirituality in the Age of Science

My question about love was just one of many I posed to scientists, philosophers, ethicists, and faith leaders as I worked these past few years on a public-television series titled Searching: Our Quest for Meaning in the Age of Science, which will premiere in early January 2023. I wanted to know: What does it mean to be human in a world of increasing science and technology? How do complex human experiences such as falling in love or feeling a connection to nature or appreciating beauty emerge from the material brain—a collection of atoms and molecules?

I call myself a spiritual materialist. As a scientist, I’m a materialist. Not in the sense of seeking happiness in cars and nice clothes, but in the literal sense of the word: the belief that everything is made out of atoms and molecules, and nothing more. Further, I believe that the material stuff of the universe is governed by a small number of fundamental laws. Yet I have had transcendent experiences. I’ve made eye contact with wild animals. Looking up at the stars one summer night, I lost track of my body and felt that I was merging with things far larger than myself. I feel connected to other people and to the world of living things. I appreciate beauty. I’ve experienced awe. Of course, all of us have had similar feelings and moments, like the birth of a child or watching a solar eclipse. Although these experiences vary widely, they have sufficient similarity that I’ll gather them together under the heading of “spirituality.” So I’m a spiritual materialist.Many people associate spirituality with an all-powerful, intentional, and supernatural God. I respect such beliefs. But my concept of spirituality does not require them. It is my view that all human experiences, including spirituality, are compatible with a fully scientific view of the world, even while some are not reducible to zeros and ones. I believe not only that these experiences are rooted in material atoms and molecules but also that they can be explained in terms of the forces of Darwinian evolution.

As our nation and our world have become more polarized in recent years, the dialogue between science and spirituality has assumed greater and greater importance. The two are not mutually exclusive, and yet too many people act as though they are. We human beings are capable of inventing antibiotics and smartphones, and we are also capable of composing symphonies or being awestruck by the melting red glow of a setting sun. We are experimenters, and we are also experiencers.

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Primary among these “spiritual” experiences is the feeling of connection—to nature, to other people, and to the cosmos as a whole. In a previous essay, I described the evolutionary basis for our feelings of connection to nature. As we humans have spent more than 99 percent of our 2-million-year history living outdoors, an attentiveness to nature would have had great survival benefit—for such necessities as habitat selection, foraging for food, and reading the signs of an upcoming storm.

Just as evolutionary forces probably shaped our feelings of a deep connection to nature, they also probably shaped our need for connection to other human beings, which, in turn, is related to our feelings of being part of something larger than ourselves. In early hunter-gatherer groups, which occupied most of human history, members of the group would have been highly dependent on one another for survival. Danger was always nearby. The hunters went out for food, while other adults protected the children, kept the fire going, and fortified the cave in communal settings. Being shunned or separated from the group probably would have brought a quick death. The social psychologist Cindy Frantz of Oberlin College says that there are definite psychological similarities between the kinds of relationships we have with nature and those we have with people. “One of the adaptive strategies that humans have,” she told me, “is that we live in these cooperative social groups. For our ancestors, to not be a member of the group would have meant a dramatically higher chance of dying and not passing on their genes … We evolved these core social motives because they helped keep people alive. The most powerful of those is the need to belong.”

One of the more thought-provoking conversations I recently had was at the La Ferrassie rock shelter in Southern France. Bruno Maureille, a local anthropologist, told me that skeletons found there showed that early humans, as long ago as 40,000 years, buried members of their group with ritual care. Much of nature we consider beautiful because we are part of nature. Coppery clouds. The winding swirl of a seashell. The splaying of hues in a rainbow. The reflection of stars on the surface of a still pond at night. We grew up in nature, evolutionarily speaking. Of course, there’s also a cultural component to the notion of beauty, especially when it comes to the physical beauty of people: Elongated earlobes are considered beautiful by the Masai in Kenya. For centuries, the Chinese bound the feet of girls, believing that small feet were beautiful, feminine, and a sign of refinement. But some concepts of beauty seem universal.

It is not hard to argue that an appreciation of color and form and other aspects of beauty had survival benefit in their relation to sexual attraction. The primal and evolutionary force behind sexual attraction, of course, is procreation, and procreation is most successful when both partners are healthy and vigorous. Health and vigor, in turn, are associated with well-formed body shape, smooth skin, good color, striking facial features, and other elements of bodily “beauty.” In fact, the neurological reactions to beauty trigger some of the same pleasure centers in the brain as eating, sex, and drugs. Both Darwin and Freud opined on the connection between an appreciation for beauty and sexual drive.

Of course, most experiences of beauty do not involve sexual attraction. But the more general appreciation of beauty could well be a by-product of a trait, like sexual attraction, that did (and does) have survival benefit. Evolutionary biologists call such by-products “spandrels.” The botanist and geneticist Hugo Iltis wrote that “man’s love for natural colors, patterns, and harmonies … must be the result of natural selection through eons of mammalian and anthropoid evolution.”

Our sensitivity to beauty, combined with our kinship with the natural world, has some surprising aesthetic manifestations and interconnections. Take the “golden ratio.” Biologists, architects, psychologists, and anthropologists have long noted that we find especially pleasing those rectangles whose ratio of long side to short side is approximately 3 to 2. That ratio is close to what is called the “golden ratio,” sometimes called the “golden mean.” Two numbers are in the golden ratio if the ratio of the larger number to the smaller is the same as the ratio of their sum to the larger number. From this seemingly simple definition, we can determine that the golden ratio is 1.61803… .

Now we enter the kingdom of magic. The 12th-century Italian mathematician Leonardo Fibonacci discovered an interesting sequence of numbers, called the “Fibonacci sequence”:

0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, …

Each number of the sequence, after the zero, is the sum of the previous two numbers. As you can test for yourself, the ratio of a number in the sequence to the one before it approaches the golden ratio as we go to bigger and bigger numbers. For example, 21/13 = 1.615, 34/21 = 1.619, 55/34 = 1.6176. So this special series of numbers is closely related to the golden ratio. Even at this point, anyone with an appreciation for mathematics can see much beauty in the golden ratio and its relation to the Fibonacci series of numbers.

But there is much more to this natural magic. Consider a spiral constructed by the quarter circles connecting the opposite corners of a series of ever-bigger squares whose sides are the numbers in the Fibonacci series, as shown in the diagram below:

illustration of the fibonacci ratio spiral on a graph

Astonishingly, many biological organisms embody this spiral. For example, seashells and aloe polyphylla:

aloe plant with leaves growing in the fibonacci spiral


With its ubiquity in nature, the golden ratio is, not surprisingly, pleasing to the human eye. Architects, ancient and modern, have built it into their constructions, sometimes unconsciously. For example, the Great Pyramid of Giza (2560 B.C.) has a slant height of 186.3 meters and a base length of 115.2 meters with a ratio of 1.6172, almost exactly equal to the golden ratio.

The mechanical engineer Adrian Bejan at Duke University has offered an evolutionary explanation, based on the eye and the brain, as to why we find the golden ratio so appealing. Bejan argues that the eye and brain would have evolved to maximize the ease of flow from the visual plane to the brain. If we consider a rectangle, the time for the eye to scan the area of the rectangle is smallest when the eye can scan the horizontal length in the same time it takes to scan the vertical. After doing an analysis of the geometry of the eye, Bejan finds that the eye scans in the horizontal direction about 1.5 times as fast as in the vertical direction. Thus, the optimal value of the ratio, which minimizes the time to scan the entire rectangle, is about 3/2, not far from the golden ratio.

It is but a short step from Bejan’s analysis to argue that because many objects in nature exhibit the golden ratio in their construction, our eyes would naturally have evolved to optimize the flow of information to the brain for objects with this ratio. And a short step from there to argue why this ratio is so pleasing to the eye. The golden ratio is built into us, just as it is built into seashells and aloe plants. Our aesthetic of beauty is literally an expression of our oneness with nature.

Understanding these scientific explanations of why I appreciate beautiful things does not in the slightest diminish my pleasure and delight in gazing upon coppery clouds or spiraling seashells or the reflection of stars in the water. In fact, they enhance my pleasure, emphasizing my connections to the natural world. For me, the elegance of the mathematics of the Fibonacci series, the presence of that particular beauty in seashells and plants, and my own biological affinity for such beauty are all of a piece, a wholeness, a profound connectedness of all living things.

The bedrock of all human mental experiences, including those I have grouped under the heading of spirituality, is consciousness: the first-person participation in the world; the awareness of self; the feeling of “I-ness”; the sense of being a separate entity in the world; the simultaneous reception and witnessing of visual images, sound, touch, memory, thought; the ability to conceive of the future and plan for that future.

Consciousness almost certainly exists on a spectrum, from automatic responses to the surrounding environment at the low end to self-awareness, ego, and the ability to plan ahead at the high end. Amoebas may not be conscious in any meaningful way, while crows and dolphins and dogs almost certainly are.

The highest level of consciousness, the primal human experience, is so unique, so hard to describe, so different from experiences with the world outside our bodies that we may never be able to fully capture consciousness with brain research. Like Professor Desimone at MIT and almost all biologists and neuroscientists, I firmly believe that consciousness and all mental experiences are sensations brought about by the chemicals and electrical currents in the brain. But we may never be able to show how this highest level of consciousness emerges step-by-step from the neurons and synapses of the material brain.

In his famous 1972 paper “What Is It Like to Be a Bat?” the American philosopher Thomas Nagel defines consciousness in a way that underscores the near impossibility of crossing the subjective/objective divide: “Fundamentally an organism has conscious mental states if and only if there is something that it is like to be that organism … We may call this the subjective character of experience.” How can we feel what a bat feels or what a dog feels or even another human being?

Even though we may not have a full explanation of that mysterious sensation we call consciousness, a great deal of evidence suggests that it originates in the material brain: the association between “awareness” and physical neurons of the brain; the connection of behavioral manifestations of consciousness to material brain structures, a connection particularly evident when the brain is damaged; and the observed manifestations of different levels of consciousness through the animal world.

Another name for awareness is “attention.” In the millions of visual images, sounds, smells, and other sensory inputs that bombard the brain every second, what mechanism allows us to pay attention to some things and disregard others? What happens in the brain that enables us to ignore a leaking faucet but pay attention to a knock on the door? In 1990, the neuroscientist Christof Koch and the molecular biologist Francis Crick proposed that paying attention to a sight or sound is associated with the synchronous firing of neurons. Attention is not consciousness. However, it is probably a necessary condition for consciousness, and its neural mechanics are a step along the way to understanding the material basis of consciousness.

The attention proposal was supported in 2014 by the neuroscientists Desimone and Daniel Baldauf. They presented a series of two kinds of images—faces and houses—to their subjects in rapid succession, like passing frames of a movie, and asked them to concentrate on the faces but disregard the houses (or vice versa). The images were “tagged” by flashing them at two different frequencies—a new face image every two-thirds of a second and a new house image every half second. The researchers then put a helmetlike container on the subject’s head that could detect tiny local magnetic fields inside the brain and thus localized brain activity. By monitoring the frequencies of the magnetic and electrical activity of the subject’s brain, Desimone and Baldauf could determine where in the brain the house and face images were being directed and processed.

The scientists found that when the subjects were told to concentrate on the faces but disregard the houses, the neurons in the face-recognition portion of the brain fired in synchrony, like a group of people singing in unison, while the neurons in the house location fired like a group of people singing out of synch, each beginning at a random part of the song. And when the subjects concentrated on houses and disregarded the faces, the reverse happened. Evidently, what we perceive as “paying attention” to something originates, at the cellular level, in the synchronized firing of a group of neurons, whose rhythmic electrical activity rises above the background chatter of the immense neuronal crowd.

Many other manifestations of consciousness are associated with the material brain. Psychiatrists, psychologists, and neuroscientists have developed questionnaires for patients with brain damage to measure their degree of self-awareness and functioning ability. The questionnaires are administered to three groups: the patient, the patient’s family, and an observing clinician. One such questionnaire, developed by Mark Sherer at the Baylor College of Medicine and the University of Texas Medical School at Houston, asks these questions, among others:

How well can the patient do on tests that measure thinking and memory skills now as compared to before his/her injury? How good is the patient at keeping up with the time and date and where he/she is now as compared to before his/her injury? How good is the patient’s memory for recent events now as compared to before his/her injury? How good is the patient at planning things now as compared to before his/her injury?

Not surprisingly, the results of such studies show low scores as measured by the family members and clinicians but not particularly low as measured by the patients themselves. Evidently, when a person loses self-awareness, this is not so apparent to the person themselves. Such awareness of one’s own lack of awareness would require another, “supervisory” part of consciousness unaffected by the brain injury. It is also possible that people with brain injury are defensive about their loss of abilities and overrate their mental capabilities. Self-reporting is always a tricky business. Thus, most reliable here are the reports of family members and clinicians.

Autobiographical memory is an important feature of self-identity and self-awareness. Imagine going to a cocktail party with strangers under the restriction that you were not allowed to say anything about your history. Numerous studies have shown that autobiographical memory is diminished by brain damage and dementia. Consider, for example, Alzheimer’s, which is a disease that destroys memory and thinking ability. Autopsies of the brains of Alzheimer’s patients reveal deposits of a protein called amyloid around brain cells, and plaques of another protein, called tau, that cause “tangles” of brain cells. Researchers have also found that as brain cells become affected in Alzheimer’s disease, there is a decrease in the chemical neurotransmitters, such as acetylcholine, that send signals between neurons. These findings not only show the clear correlation between memory (as well as associated consciousness) and the physical brain; they also emphasize the importance of the communication between neurons as a crucial part of consciousness and higher intelligence in general.

One way of exploring the emergence of consciousness in the human brain is to study the behavioral correlates of consciousness in other animals and map out a gradation of consciousness with increasing brain capacities. Dolphins, which have almost as many cortical neurons as humans (long-finned pilot whales actually have more than humans), have shown clear signs of self-awareness and play. In a famous experiment demonstrating self-recognition, a mirror is placed in a pool with dolphins. The dolphins swim up to the mirror, look at it for a few moments, and swim away. Then marks are placed on the dolphins’ bodies. Now the dolphins spend longer looking at themselves in the mirror. Evidently, they have noticed that something has changed about their body. Out in the open ocean, dolphins will stop what they are doing when a large boat approaches, and ride in its bow wave. Some years ago, I went sailing in the Aegean Sea. A dolphin not only swam alongside me but catapulted itself over the stern of the boat. To all appearances, it was having fun.

Monkeys play. Kittens chase one another and paw at a hanging string. Sea lions will toss sticks to each other. Among animals with higher levels of consciousness like us, we can see striking similarities. Yet we can recognize aspects of human cognition even at the lower end of the spectrum of consciousness.

Even though we do not understand in detail how consciousness and complex human experiences emerge from the material brain, there are many other known phenomena in which the behavior of complex systems is often not evident or comprehensible in the individual material parts of those systems.

Such behaviors are called “emergent phenomena.” An example would be the behavior of certain kinds of fireflies. When a group of these insects congregate in a field at night, at first they flash randomly, like the blinking lights of a Christmas tree. But after a few moments, the fireflies begin flashing in unison. Such behavior could not be predicted by the study of an individual firefly, but can be seen readily in groups. Another example is the large and complex mounds built by termites, called “termite cathedrals.” The cathedrals sometimes have elaborate galleries and chimneys to control airflow, temperature, and humidity.

Building such a complex structure would seem to require some kind of master plan, executed by the hundreds of thousands of termites in the colony. But individual termites, which are blind, cannot perceive even the overall shape of a mound, much less direct its design. Somehow, the complex mound arises from the collective behavior of the full colony. Researchers believe that termites exchange chemical signals with one another and also respond to cues from airflow and temperature, which are affected by the shape of the mound.

Now consider the human brain, with 100 billion firefly-like neurons. We can understand everything about how individual neurons work—the way that electrical ions are exchanged across the neuron membranes, the way that an electrical current is passed along the neuron, the way that a neuron chemically connects to another neuron—but we still cannot fill in all the blanks for how the collection of neurons produces the sensation we call consciousness. Yet neuroscience suggests to us that the emergence of consciousness in advanced brains such as the human brain, although enormously more complex than fireflies or termite cathedrals, is not different in kind. In particular, consciousness can emerge from the collective interaction of billions of neurons, following known laws of chemistry, physics, and biology, without the intervention of some additional ethereal or “psychic” force.

I will end with a final illustration of spiritual materialism, as I see it. There is very good scientific evidence that all the atoms in our bodies, except for hydrogen and helium, the two smallest atoms, were manufactured at the centers of stars. If you could tag each of the atoms in your body and follow them backwards in time, through the air that you breathed during your life, through the food that you ate, back through the geological history of the Earth, through the ancient seas and soil, back to the formation of the Earth out of the solar nebular cloud and then out into interstellar space, you could trace each of your atoms, those exact atoms, to particular massive stars in our galaxy’s past. At the end of their lifetimes, those stars exploded and spewed out their newly forged atoms into space, later to condense into planets and oceans and plants and your body at this moment. We have seen such stellar explosions with our telescopes and know they occur.

If, instead of going backwards in time, I were to go forward in time, to my death and beyond, the atoms in my body will remain, only they will be scattered about. Those atoms will not know where they came from, but they will have been mine. Some of them will once have been part of the memory of my mother dancing the bossa nova. Some will once have been part of the memory of the vinegary smell of my first apartment. Some will once have been part of my hand. If I could label each of my atoms at this moment, imprint each with my Social Security number, someone could follow them for the next thousand years as they floated in air, mixed with the soil, became parts of particular plants and trees, dissolved in the ocean, and then floated again to the air. And some will undoubtedly become parts of other people, particular people. So, we are literally connected to the stars, and we are literally connected to future generations of people. In this way, even in a material universe, we are connected to all things future and past. I don’t believe in miracles, but I do believe in the miraculous.

This essay is adapted in part from Alan Lightman’s forthcoming book, The Transcendent Brain: Spirituality in the Age of Science.

The Transcendent Brain: Spirituality in the Age of Science

Alan Lightman, a physicist and novelist, teaches at MIT. He is the author of several books and the host of the public television series Searching: Our Quest for Meaning in the Age of Science.