What is love? Answers from biology*

What is love? Answers from biology*

Love is no longer the exclusive domain of artists, philosophers, and lovers, but it has become a topic of scientific interest given its importance in human life. However, each of us may have our definition of love, from a biological point of view it has been characterized as an integral phenomenon that involves our brain and our hormone-producing organs, such as the pituitary gland and the adrenal gland. Love involves several chemical messengers that provide a range of sensations ranging from pleasure, euphoria, trust, and security, to anxiety, obsession, and depression. It is a phenomenon that includes characteristic behavioral, cognitive, and emotional patterns.

All these complex feelings and behaviors experienced in love have led researchers to study each component and thus understand the biological bases that support it. For example, some studies investigate the brain regions that participate in falling in love, while others, through molecular genetics experiments, try to understand the bases of emotional ties and social interactions.

From a biological point of view, we can distinguish two types of love: romantic or couple love and filial love (maternal or paternal). Both are essential for the survival of our species, since the former generally leads to reproduction, while the latter allows the offspring to receive the appropriate care for their development. Let us remember that in the human species (as well as in other primates), the offspring require the care of their mother or father for a considerable time. It has also been established that romantic love generates security and trust, which ensures protection in changing environmental situations. Thus, the biological meaning of love is found in the perpetuation and survival of our species.

Butterflies in the stomach

Butterflies in the stomach

The first phase of a romantic relationship is falling in love, which is transitory, dominated by attraction processes, and begins with perception and the consequent pleasure produced by the stimulation of our senses. In ancient times, the most important stimulus (perhaps still is) in a romantic relationship, and which for a long time generated the phrase “love at first sight”, was precisely sight, given the importance that this sense has acquired for us throughout evolution, without neglecting the stimulation of hearing, smell, taste, and touch. However, in these modern times, advances in communication have meant that often the first contact between two people is virtual, through email or social networks, and that without having olfactory, auditory, or even visual stimulation, falling in love can be triggered.

When we fall in love

 impressive physiological changes occur in our bodies. The production of hormones (chemical messengers secreted by a gland and with different effects on the mind and body) changes, our mood changes noticeably and we even have a different perception of reality.

It has been found that during the first few months of falling in love, there is an increase in cortisol levels, a steroid hormone related to stress. In addition, the production of testosterone, a sexual hormone that is more abundant in men than in women, decreases in men (see  ¿Cómo ves?  No. 134). In contrast, in women, it increases, which causes men to modify their behavior a little and appear calmer, while women may be more alert or even aggressive.

It is known that people in love experience moderate states of anxiety and stress, which are manifested through an increase in sweating, blood pressure, heart rate, and intestinal peristaltic movements (the famous “butterflies in the stomach”). As long as these physiological changes are moderate, being in love is beneficial for health: it is a very motivating, inspiring and comforting state that keeps people alert and optimistic. It is known that in the long run, love reduces stress after this uncertain stage of falling in love.

With all my heart?

With all my heart

As romantic as it may sound to say or be told “I love you with all my heart,” all of our thoughts, feelings, and dreams come from brain activity. There is a communication system in our brain, made up of different interconnected structures, known as the limbic system, and it is what allows us to experience the full range of emotions that occur in our lives.

It is known that some brain regions are involved in both maternal love and romantic love. It has been proposed that both have similar evolutionary origins and are manifested through analogous cellular mechanisms. Thus, in experiments where brain imaging is analyzed using techniques such as functional magnetic resonance imaging, it has been seen that showing photographs of a child to a mother or of a loved one to a loving partner activates similar regions of the limbic system, although there are other structures exclusive to each type of love. For example, structures related to sexual desire, such as the hypothalamus (a brain region responsible for many functions, including sexual behavior), are only activated in the case of romantic love.

In subjects who are deeply in love,

the presentation of photographs of the loved one activates regions of the brain related to positive emotions, which cause well-being, such as the insula, the cingulate cortex and the caudate and putamen nuclei. At the same time, other brain regions are deactivated, such as the amygdala and the frontal and prefrontal cerebral cortex, which are associated with fear, sadness and the establishment of a critical judgment of the behavior and intentions of other people. This seems to be related to the fact that when we are in love, everything or almost everything seems ideal to us in our partner; we can then understand why it is said that “love is blind.”

The molecules of love

The molecules of love

Given the range of sensations involved in the phenomenon of love, it is not reasonable to think that there is a “love molecule”; however, there are substances closely linked to the emotional states that occur in romantic love and maternal behavior, in addition to being fundamental in the establishment of emotional ties between individuals. These substances are hormones such as vasopressin and oxytocin, neurotransmitters (molecules responsible for communication between neurons) such as dopamine and serotonin, and endogenous opiates  —molecules produced in our brain related to sensations of pleasure and the reduction of pain—such as endorphins and enkephalins.

Vasopressin and oxytocin are peptides, i.e. substances made up of amino acids, which are the components of proteins. They are made up of nine amino acids that are produced mainly in the hypothalamus and that have vital and diverse actions in our organism. For example, vasopressin, also called antidiuretic hormone, participates in the regulation of the water content of our body, while oxytocin is essential for labor and lactation. In addition to these functions, both have been found to participate in the display of social behaviors, the establishment and maintenance of bonds between mother and child, and between couples.

In several mammalian species,

including humans, oxytocin is released during labor and lactation, which is important for the establishment of the mother-infant relationship. Intracerebral administration of oxytocin to female sheep induces them to care for other’s offspring and exhibit maternal behavior. It has also been found that during coitus there is an increase in the secretion of oxytocin and vasopressin, which strengthens the bond between couples. In prairie voles, vasopressin has been shown to stimulate paternal behavior, the maintenance of bonds between couples, and monogamous behavior.

In the case of serotonin, dopamine, and enkephalins, it is known that they participate in the generation and reinforcement of many of the emotions that occur during romantic relationships through their action on the brain structures related to pleasure and reward sensations. It is also known that these chemical messengers can regulate the production and effects of oxytocin and vasopressin. If there are molecules involved in love, then could we make love potions or have a cure for lovesickness? Despite the great herbal tradition of different countries, including ours, and the advances in the synthesis of organic compounds, there are still no magic potions to make the person we are interested in fall in love with us. It is also necessary to remember that oxytocin, vasopressin and other molecules mentioned participate in the regulation of many functions and not only in the maintenance of sentimental ties, so their administration can have important side effects on our body.

For some years, perfumes containing oxytocin or synthetic pheromones

, either male or female, have been marketed, which are supposed to attract the opposite sex. (See  What Do You See?  No. 88.) Pheromones are volatile substances that we produce in glands in the skin, such as sweat glands, and which stimulate the olfactory system. Although these molecules activate a region in the nose called the vomeronasal organ and have been found in laboratory conditions to produce different physiological responses in humans—including changes in breathing, heart rate, and levels of hormones such as gonadotropins and testosterone—it is unknown whether they have effects outside the experimental setting and they obviously would not be specifically directed toward any particular person, so if we fill ourselves with these pheromones we could run the risk of attracting the wrong person. Given the different sensations of pleasure that love causes – which can even generate certain addictive behaviors – when we suffer disappointment or someone “breaks up” with us, there is an absence of all these positive, pleasurable, and comforting sensations, which leads to “lovesickness”: our health deteriorates due to chronic stress; there is confusion and significant states of depression can be reached. If this were to happen, psychological or psychiatric assistance would be required, and, in serious cases, the use of antidepressant drugs, many of which increase serotonin levels. According to love experts, the best remedy for a breakup is to go through a period of mourning for the loss of the loved one and then… fall in love again.

Infidelity and genes

Infidelity and genes

In romantic love, one of the components that is generally decisive for maintaining a relationship is fidelity, which in most societies refers to having only one sexual partner at a time. In addition to all the social factors that can influence the establishment of ties with one or more partners at the same time, scientists have wondered if there is a biological basis for fidelity and it seems that the answer could be positive.

There are rodents of closely related species of the same genus ( Microtus ) that have established themselves in different habitats, for example in the prairie and in the mountains, which show very evident monogamous or polygamous behavior. These species show differences in the concentration and distribution of vasopressin receptors in the brain; the receptors are proteins that bind to chemical messengers, such as hormones or neurotransmitters, so that they can carry out their effects on the cell. It has been seen that the vasopressin receptor gene presents variants between one species and another. In molecular biology experiments in which the gene from the monogamous species is transferred to the polygamous species at very early stages of embryonic development, the latter displays monogamous behavior in the adult stage.

These experiments motivated a group of Swedish and American researchers

, led by Hasse Walum of the Karolinska Institute in Sweden, to study the relationship between variants of the vasopressin receptor gene, called AVPR1A, and couple bonding in humans. In 2008, the results of the research were published in the journal  Proceedings of the National Academy of Sciences: an association was found between variants of this gene in men and emotional bonds with their partners, showing that Swedish men with a particular variant of the gene were more likely to remain single or, if married, to have marital problems due to weak ties with their partner and the establishment of extramarital sexual relations. Variants of the vasopressin receptor gene have not been characterized in other populations, so it is unknown whether these variants are exclusive to Nordic populations.

Although it has been speculated that to find the ideal partner, or at least a faithful partner, in the future it would be enough to study the genes that participate in our social behaviors – such as the receptors for vasopressin, oxytocin, or dopamine – and thus determine whether the man or woman has a certain predisposition to have more than one partner at the same time, the matter is not so simple. The fact, for example, of having a particular variant of the gene for the vasopressin receptor, or of some other gene involved in emotional ties and social relationships, will not necessarily determine monogamous or polygamous behavior; our characteristics and behaviors are the results of the interaction of our genes with the environment and many environmental factors modulate relationships.

Forever… or not

Forever… or not

One of the most recurrent and still unanswered questions is how long love lasts and if it can last forever. Various groups of psychologists and psychiatrists have speculated that falling in love lasts a few months and then moves on to a more conscious and critical state of reality, in which the different characteristics of the couple begin to be valued; it is then when, in theory, we can define if the relationship we have is trustworthy, pleasant and comforting.

The time it takes to move from one stage to another and to maintain the second stage, which is the most difficult, depends on many factors; among them, the processes of memory and learning and the adaptation of our sensory systems have been highlighted. It has been proposed that in a relationship that has just begun, there is a large number of stimuli and novel situations that cause interest, pleasure, and a good dose of learning in the other person. But after a certain time, the stimuli cease to be novel, learning decreases and routine behavioral patterns are established that no longer arouse the initial interest and motivation. For the above, it is said that the secret is to vary the activities and behaviors that occur in a relationship.

Many times a romantic relationship leads to marriage and shared life,

where again some situations generate learning processes. When these processes are about to be exhausted, the birth of children often occurs, which possibly causes the most dramatic and permanent changes in terms of behavior and learning in the life of an adult. However, in general, after a few years, there are situations in which there is no longer pleasure or learning in the relationship; for this reason, it has been said that if there is interest from both parties, any romantic relationship must be constantly nourished and reinvented. In recent years, several groups of psychologists have discovered that among the ingredients that give greater strength to a relationship for a considerable time are communication, commitment, trust, intimacy, and the celebration of important moments for one of the members of the relationship, more than support in unfavorable situations. So if you want to stay with your partner, do not hesitate to celebrate happy moments with him or her.

Comprehensive knowledge

Comprehensive knowledge

Given the importance of maternal or paternal love, as well as romantic or couple love, in the perpetuation and maintenance of human beings and the different areas of our lives (for example, it is known that workers who have a satisfactory romantic relationship have better job performance), a scientific approach to this phenomenon from different areas of knowledge is essential. This will allow us not only to understand fully the processes we experience when we love, are loved, stop loving or are no longer loved, but also to learn more about each of the components of love, its evolutionary importance, the brain regions and chemical messengers that participate in it, how the brain organizes the deployment of very diverse behaviors and the molecular mechanisms that lead to the different emotions being experienced.

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