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The biology of romantic love has been explored by such biological sciences as evolutionary psychology, evolutionary biology, anthropology and neuroscience. Specific chemical substances such as oxytocin and dopamine are studied in the context of their roles in producing human experiences, emotions and behaviors that are associated with romantic love.
Bode and Kushnick undertook a comprehensive review of romantic love from a biological perspective in 2021. [1] They considered the psychology of romantic love, its mechanisms, development across the lifespan, functions, and evolutionary history. Based on the content of that review, they proposed a biological definition of romantic love: [1]
Romantic love is a motivational state typically associated with a desire for long-term mating with a particular individual. It occurs across the lifespan and is associated with distinctive cognitive, emotional, behavioral, social, genetic, neural, and endocrine activity in both sexes. Throughout much of the life course, it serves mate choice, courtship, sex, and pair-bonding functions. It is a suite of adaptations and by-products that arose sometime during the recent evolutionary history of humans. [1]
Contemporary literature also draws distinctions between romantic love and the attachment system theorized by attachment theorists such as John Bowlby. [2] [3] [4] Romantic love is related to or involves attachment over time, but is thought to also involve additional brain systems. [2] [5] [3]
Courtship attraction is a phenomenon exhibited by many species which serves the role of mate choice, or intersexual selection. [6] This refers to physical and behavioral characteristics, as well as brain systems which motivate an individual to pursue a preferred mating partner. [6] Courtship attraction shares similar behaviors with romantic love in humans, and both involve activation of dopaminergic reward circuits. [6] In most species, courtship attraction lasts only minutes, hours, days or weeks, but romantic love in humans can last much longer, 12–18 months or more. [6]
It has been proposed that courtship attraction and romantic love are related phenomena, either that romantic love evolved as a form of courtship attraction, [6] or that courtship attraction is one of several interrelated components. [3]
Helen Fisher and her colleagues proposed that the brain systems involved with mammalian reproduction can be separated into at least three parts: [2] [5]
Neuroscientists currently believe that the basic emotions arise from distinct circuits (or systems) of neural activity; that humans share several of these primary emotion-motivation circuits with other mammals; and that these brain systems evolved to direct behavior. It is hypothesized that among these primary neural systems are at least three discrete, interrelated emotion-motivation systems in the mammalian brain for mating, reproduction, and parenting: lust, attraction, and attachment. [5]
The team suggests that these systems tend to act in unison, but may become disassociated. For example, a person in a long-term partnership may feel attachment for their spouse, but become attracted to somebody else. [5] Lisa Diamond has argued based on independent emotions theory and other evidence that people can 'fall in love' without sexual desire, even in contradiction to their sexual orientation. [7]
Adam Bode has suggested Fisher's model, while useful and the predominant one for a time, is oversimplified and proposes five systems: [3]
Bode suggests that the systems of bonding attraction, obsessive thinking and attachment together comprise the core of romantic love. [3] He suggests these three systems evolved by co-opting brain systems originally for mother-infant bonding, and courtship attraction and sexual desire are causally linked adjuncts. [3]
Academic literature has drawn a parallel between romantic love and the mother-infant dyad since the 1980s. [8] In 1998, Leckman & Mayes compared features of romantic love and early parental love, and suggested they share common neurobiologic systems. [9] [3] Leckman & Mayes speculate that there is an evolutionary reason behind the similarity, asking "If some part of the behavioral repertoire works in one context to help create and sustain a relationship, why not borrow it to form another?" [9] In 2004, Bartels and Zeki compared romantic love and maternal love with fMRI. [10] [3]
Lisa Diamond has suggested that adult pair bonding is an exaptation. [3] [7] Adam Bode writes that "exaptation is when a trait retains its original form but takes on a new function; co-option is the process whereby any trait takes on a new function, regardless of whether the original form is retained or not." [3]
Bode has proposed that romantic love evolved by co-opting mother-infant bonding. [3] The co-option theory says that the genes that regulate mother-infant bonding were recreated and took on a new function. The theory is based on a literature arising from research on prairie voles that pair bonding uses the same mechanisms that mother-infant bonding use as well as the available human evidence. The theory was used to critique a previously asserted evolutionary theory of romantic love proposed by Helen Fisher, [3] that romantic love is a form of courtship attraction. [6] Bode's theory explains not only one process in the emergence and subsequent evolution of romantic love, but also proposed a new model of the mechanisms of romantic love. [3]
Evolutionary psychology has proposed several explanations for love. The evolutionary pathway for romantic love predates mammals. The pattern of behaviors associated today with love are prevalent throughout the animal kingdoms and beyond. [11]
Monkey infants and children are for a very long time dependent on parental help. Love has therefore been seen as a mechanism to promote mutual parental support of children for an extended time period. Another is that sexually transmitted diseases may cause, among other effects, permanently reduced fertility, injury to the fetus, and increase risks during childbirth. This would favor exclusive long-term relationships reducing the risk of contracting an STD. [12]
From the perspective of evolutionary psychology the experiences and behaviors associated with love can be investigated in terms of how they have been shaped by human evolution. [13] For example, it has been suggested that human language has been selected during evolution as a type of "mating signal" that allows potential mates to judge reproductive fitness. [14] Since Darwin's time there have been similar speculations about the evolution of human interest in music also as a potential signaling system for attracting and judging the fitness of potential mates. [15] It has been suggested that the human capacity to experience love has been evolved as a signal to potential mates that the partner will be a good parent and be likely to help pass genes to future generations. [16] Biologist Jeremy Griffith defines love as 'unconditional selflessness', [17] suggesting utterly cooperative instincts developed in modern humans' ancestor, Australopithecus . Studies of bonobos (a great ape previously referred to as a pygmy chimpanzee) are frequently cited in support of a cooperative past in humans. [18]
There have been fewer than 45 biological studies of romantic love. [19] One view in biology is that there are three major drives in love – libido, attachment, and partner preference. [20] [21] The primary neurochemicals (neurotransmitters, sex hormones, and neuropeptides) that govern these drives are testosterone, estrogen, dopamine, oxytocin, and vasopressin. [20] [22]
Central dopamine pathways mediate partner preference behavior, while vasopressin in the ventral pallidum and oxytocin in the nucleus accumbens and paraventricular hypothalamic nucleus mediate partner preference and attachment behaviors. [20] [23] Sex drive is modulated primarily by activity in the mesolimbic dopamine pathway (ventral tegmental area and nucleus accumbens). [20] Trace amines (e.g., phenethylamine and tyramine) play a critical role in regulating neuronal activity in the dopaminergic pathways of the central nervous system. [24]
Testosterone and estrogen contribute to these drives by modulating activity within dopamine pathways. [20] Adequate brain levels of testosterone seem important for both human male and female sexual behavior. [25] Norepinephrine and serotonin have a less significant, contributing role through their neuromodulatory effects upon dopamine and oxytocin release in certain pathways. [20]
The chemicals triggered that are responsible for passionate love and long-term attachment love seem to be more particular to the activities in which both persons participate rather than to the nature of the specific people involved. [21] There is mixed evidence about the role of cortisol in romantic love. [26]
A less speculative account of the neurochemistry of romantic love was provided by Bode & Kushnick in 2021. [26] While they recognize that other factors play a role, they summarize the available human endocrinological evidence that implicates testosterone, dopamine, oxytocin, serotonin, cortisol, and nerve growth factor in romantic love. There is no evidence that estrogen and norepinephrine play a major role in romantic love (although they might) and only neuroimaging and genetic evidence of vasopressin's involvement. [27] [28]
The role of the limbic system in emotion was first explained by James Papez in 1937 within his paper titled "A proposed mechanism of emotion". The model described is known as the Papez circuit. The Papez circuit highlighted the presence of neuronal pathways between the vestibular and the limbic system. [29] The vestibular apparatus is in the inner ear and coordinates the body balance and movement. This requires extensive neuronal networking. Vestibular stimulation, which comes from the apparatus, can cause changes in mood and emotion. It can also impact emotions either independently or as part of the general limbic system networks by influencing the hypothalamus. These emotions can include extreme passivity, loss of drive/motivation, excessive eating and drinking, and rage and violent behavior. [29] Studies show Romantic Love uses reward and motivation systems to focus on a specific individual. The limbic cortical regions process individual emotion factors. [30] In A General Theory of Love, three professors of psychiatry from UCSF provide an overview of the scientific theories and findings relating to the role of the limbic system in love, attachment and social bonding. They advance the hypothesis that our nervous systems are not self-contained, but rather demonstrably attuned to those around us and those with whom we are most close. This empathy, which they call limbic resonance, is a capacity which we share, along with the anatomical characteristics of the limbic areas of the brain, with all other mammals. [31] Their work builds on previous studies of the importance of physical contact and affection in social and cognitive development, such as the experiments conducted by Harry Harlow on rhesus monkeys, which first established the biological consequences of isolation.
Brain scanning techniques such as functional magnetic resonance imaging have been used to investigate brain regions that seem to be involved in producing the human experience of love. [32]
In 2000, a study led by Semir Zeki and Andreas Bartels of University College London concluded that at least two areas of the brain become more active when in love. These were foci in the media insula, which the brain associates with instinct, and part of the anterior cingulate cortex, which is associated with feelings of euphoria. [33]
Ortigue et al. found that an unconscious prime of the name of a romantic partner activated similar brain regions as when subjects were consciously aware of seeing partners' faces. [34] Subliminal priming with either a beloved's name or a favorite hobby activated emotion and motivational brain regions: caudate nucleus, insula, bilateral fusiform regions, parahippocampal gyrus, right angular gyrus, occipital cortex, and cerebellum. However, the love prime evoked more activation in bilateral angular gyri and bilateral fusiform regions than the hobby prime. These regions are associated with integrating abstract representations, and the angular gyrus in particular is involved with abstract representations of the self. The authors also found a correlation (r=0.496, p=0.002) between activation of a region of the angular gyrus with a passionate-love scale measuring subjective feelings of love. [34]
Conscious thoughts about a romantic partner activate brain regions related to reward and motivation. Ortigue et al. investigated whether unconscious priming by a partner's name could also affect motivation. They found that priming by either a beloved or a favorite hobby improved reaction times in identifying whether a string of letters was a word or not compared against priming by a neutral friend. The authors suggest this effect happens because a beloved's name "may call for a goal-directed state" and produce "dopaminergic-driven facilitation effects." [34] Similarly, the love one feels for their friends may also be biologically motivated. Isern-Mas and Gomila argue that while the love we feel for our friends is not romantic, it is still motivated through feelings of moral obligations as well as changes in the brain resulting from prosocial experiences. [35] The common motivation whether it be love romantically or through a non-intimate companion can be connected to positive feelings and rewards that in turn, form social bonds. [36] As seen in other animals as well, the immediate connections between the love of a mother and their infant impacts their personality as they age. [37] Harlow described love as a secondary drive for all animals, but it is essential for proper development. The animals that were left abandoned, had trouble socializing with others and often had personality issues as well. [37] The Behavioral Activation System (BAS), which plays a role in directing behavior, is believed to play a role in romantic love. [38]
Limerence is a state of mind resulting from romantic feelings for another person. It typically involves intrusive and melancholic thoughts, or tragic concerns for the object of one's affection, along with a desire for the reciprocation of one's feelings and to form a relationship with the object of love.
Sexual attraction is attraction on the basis of sexual desire or the quality of arousing such interest. Sexual attractiveness or sex appeal is an individual's ability to attract other people sexually, and is a factor in sexual selection or mate choice. The attraction can be to the physical or other qualities or traits of a person, or to such qualities in the context where they appear. The attraction may be to a person's aesthetics, movements, voice, among other things. The attraction may be enhanced by a person's body odor, sex pheromones, adornments, clothing, perfume or hair style. It can be influenced by individual genetic, psychological, or cultural factors, or to other, more amorphous qualities. Sexual attraction is also a response to another person that depends on a combination of the person possessing the traits and on the criteria of the person who is attracted.
Oxytocin is a peptide hormone and neuropeptide normally produced in the hypothalamus and released by the posterior pituitary. Present in animals since early stages of evolution, in humans it plays roles in behavior that include social bonding, love, reproduction, childbirth, and the period after childbirth. Oxytocin is released into the bloodstream as a hormone in response to sexual activity and during childbirth. It is also available in pharmaceutical form. In either form, oxytocin stimulates uterine contractions to speed up the process of childbirth. In its natural form, it also plays a role in maternal bonding and milk production. Production and secretion of oxytocin is controlled by a positive feedback mechanism, where its initial release stimulates production and release of further oxytocin. For example, when oxytocin is released during a contraction of the uterus at the start of childbirth, this stimulates production and release of more oxytocin and an increase in the intensity and frequency of contractions. This process compounds in intensity and frequency and continues until the triggering activity ceases. A similar process takes place during lactation and during sexual activity.
Romance or romantic love is a feeling of love for, or a strong attraction towards another person, and the courtship behaviors undertaken by an individual to express those overall feelings and resultant emotions.
The mesolimbic pathway, sometimes referred to as the reward pathway, is a dopaminergic pathway in the brain. The pathway connects the ventral tegmental area in the midbrain to the ventral striatum of the basal ganglia in the forebrain. The ventral striatum includes the nucleus accumbens and the olfactory tubercle.
The Coolidge effect is a biological phenomenon seen in animals, whereby males exhibit renewed sexual interest whenever a new female is introduced, even after sex with prior but still available sexual partners. To a lesser extent, the effect is also seen among females with regard to their mates.
Physiological psychology is a subdivision of behavioral neuroscience that studies the neural mechanisms of perception and behavior through direct manipulation of the brains of nonhuman animal subjects in controlled experiments. This field of psychology takes an empirical and practical approach when studying the brain and human behavior. Most scientists in this field believe that the mind is a phenomenon that stems from the nervous system. By studying and gaining knowledge about the mechanisms of the nervous system, physiological psychologists can uncover many truths about human behavior. Unlike other subdivisions within biological psychology, the main focus of psychological research is the development of theories that describe brain-behavior relationships.
Animal sexual behaviour takes many different forms, including within the same species. Common mating or reproductively motivated systems include monogamy, polygyny, polyandry, polygamy and promiscuity. Other sexual behaviour may be reproductively motivated or non-reproductively motivated.
Human bonding is the process of development of a close interpersonal relationship between two or more people. It most commonly takes place between family members or friends, but can also develop among groups, such as sporting teams and whenever people spend time together. Bonding is a mutual, interactive process, and is different from simple liking. It is the process of nurturing social connection.
In biology, a pair bond is the strong affinity that develops in some species between a mating pair, often leading to the production and rearing of young and potentially a lifelong bond. Pair-bonding is a term coined in the 1940s that is frequently used in sociobiology and evolutionary biology circles. The term often implies either a lifelong socially monogamous relationship or a stage of mating interaction in socially monogamous species. It is sometimes used in reference to human relationships.
Helen Elizabeth Fisher was an American anthropologist, human behaviour researcher, and self-help author. She was a biological anthropologist, a senior research fellow at The Kinsey Institute of Indiana University, and a member of the Center For Human Evolutionary Studies in the Department of Anthropology at Rutgers University. Prior to Rutgers University, she was a research associate at the American Museum of Natural History in New York City.
The reward system is a group of neural structures responsible for incentive salience, associative learning, and positively-valenced emotions, particularly ones involving pleasure as a core component. Reward is the attractive and motivational property of a stimulus that induces appetitive behavior, also known as approach behavior, and consummatory behavior. A rewarding stimulus has been described as "any stimulus, object, event, activity, or situation that has the potential to make us approach and consume it is by definition a reward". In operant conditioning, rewarding stimuli function as positive reinforcers; however, the converse statement also holds true: positive reinforcers are rewarding.The reward system motivates animals to approach stimuli or engage in behaviour that increases fitness. Survival for most animal species depends upon maximizing contact with beneficial stimuli and minimizing contact with harmful stimuli. Reward cognition serves to increase the likelihood of survival and reproduction by causing associative learning, eliciting approach and consummatory behavior, and triggering positively-valenced emotions. Thus, reward is a mechanism that evolved to help increase the adaptive fitness of animals. In drug addiction, certain substances over-activate the reward circuit, leading to compulsive substance-seeking behavior resulting from synaptic plasticity in the circuit.
Social connection is the experience of feeling close and connected to others. It involves feeling loved, cared for, and valued, and forms the basis of interpersonal relationships.
"Connection is the energy that exists between people when they feel seen, heard and valued; when they can give and receive without judgement; and when they derive sustenance and strength from the relationship." —Brené Brown, Professor of social work at the University of Houston
The reward theory of attraction claims that people are attracted to individuals exhibiting behaviors that are rewarding to them or whom they associate with rewarding events. Individuals seek to develop strong relationships with those who provide positive and fulfilling interactions that require little to nothing in return.
Definitions of sexual desire are broad and understandings of sexual desire are subjective. However, the development of various ways of measuring the construct allows for extensive research to be conducted that facilitates the investigation of influences of sexual desire. Particular differences have been observed between the sexes in terms of understanding sexual desire both with regard to one's own sexual desires, as well as what others desire sexually. These beliefs and understandings all contribute to how people behave and interact with others, particularly in terms of various types of intimate relationships.
Parental experience, as well as changing hormone levels during pregnancy and postpartum, cause changes in the parental brain. Displaying maternal sensitivity towards infant cues, processing those cues and being motivated to engage socially with her infant and attend to the infant's needs in any context could be described as mothering behavior and is regulated by many systems in the maternal brain. Research has shown that hormones such as oxytocin, prolactin, estradiol and progesterone are essential for the onset and the maintenance of maternal behavior in rats, and other mammals as well. Mothering behavior has also been classified within the basic drives.
Social monogamy in mammals is defined as sexually mature adult organisms living in pairs. While there are many definitions of social monogamy, this social organization can be found in invertebrates, reptiles and amphibians, fish, birds, mammals, and humans.
Even though intimacy has been broadly defined in terms of romantic love and sexual desire, the neuroanatomy of intimacy needs further explanation in order to fully understand their neurological functions in different components within intimate relationships, which are romantic love, lust, attachment, and rejection in love. Also, known functions of the neuroanatomy involved can be applied to observations seen in people who are experiencing any of the stages in intimacy. Research analysis of these systems provide insight on the biological basis of intimacy, but the neurological aspect must be considered as well in areas that require special attention to mitigate issues in intimacy, such as violence against a beloved partner or problems with social bonding.
Evolutionary models of drug use seek to explain human drug usage from the perspective of evolutionary fitness. Plants for instance, may provide fitness benefits by relieving pain. Proponents of this model of drug use suggest that the consumption of pharmacological substances for medicinal purposes evolved in the backdrop of human-plant coevolution as a means of self-medication. Humans thus learned to ignore the cues of plant toxicity because ingesting the bioactive compounds of plants in small amounts was therapeutic.
In psychology, a distinction is often made between two types of love. Elaine Hatfield & G. William Walster define them as:
The sex drive evolved to motivate individuals to seek a range of mating partners; attraction evolved to motivate individuals to prefer and pursue specific partners; and attachment evolved to motivate individuals to remain together long enough to complete species-specific parenting duties. These three behavioural repertoires appear to be based on brain systems that are largely distinct yet interrelated, and they interact in specific ways to orchestrate reproduction, using both hormones and monoamines. ... Animal studies indicate that elevated activity of dopaminergic pathways can stimulate a cascade of reactions, including the release of testosterone and oestrogen (Wenkstern et al. 1993; Kawashima &Takagi 1994; Ferrari & Giuliana 1995; Hull et al. 1995, 1997, 2002; Szezypka et al. 1998; Wersinger & Rissman 2000). Likewise, increasing levels of testosterone and oestrogen promote dopamine release ...This positive relationship between elevated activity of central dopamine, elevated sex steroids and elevated sexual arousal and sexual performance (Herbert 1996; Fiorino et al. 1997; Liu et al. 1998; Pfaff 2005) also occurs in humans (Walker et al. 1993; Clayton et al. 2000; Heaton 2000). ... This parental attachment system has been associated with the activity of the neuropeptides, oxytocin (OT) in the nucleus accumbens and arginine vasopressin (AVP) in the ventral pallidum ... The activities of central oxytocin and vasopressin have been associated with both partner preference and attachment behaviours, while dopaminergic pathways have been associated more specifically with partner preference.
Recent studies also highlight remarkable anxiolytic and prosocial effects of intranasally administered OT in humans, including increased 'trust', decreased amygdala activation towards fear-inducing stimuli, improved recognition of social cues and increased gaze directed towards the eye regions of others (Kirsch et al., 2005; Kosfeld et al., 2005; Domes et al., 2006; Guastella et al., 2008).
