The theory of a biological basis of love has been explored by such

biological Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary in ...

sciences as

evolutionary psychology Evolutionary psychology is a theoretical approach in psychology that examines cognition and behavior from a modern evolutionary perspective. It seeks to identify human psychological adaptations with regards to the ancestral problems they evolv ...

evolutionary biology Evolutionary biology is the subfield of biology that studies the evolutionary processes (natural selection, common descent, speciation) that produced the diversity of life on Earth. It is also defined as the study of the history of life fo ...

anthropology Anthropology is the scientific study of humanity, concerned with human behavior, human biology, cultures, societies, and linguistics, in both the present and past, including past human species. Social anthropology studies patterns of behavi ...

and

neuroscience Neuroscience is the scientific study of the nervous system (the brain, spinal cord, and peripheral nervous system), its functions and disorders. It is a multidisciplinary science that combines physiology, anatomy, molecular biology, development ...

. Specific chemical substances such as

oxytocin Oxytocin (Oxt or OT) is a peptide hormone and neuropeptide normally produced in the hypothalamus and released by the posterior pituitary. It plays a role in social bonding, reproduction, childbirth, and the period after childbirth. Oxytocin ...

are studied in the context of their roles in producing human experiences and behaviors that are associated with

love Love encompasses a range of strong and positive emotional and mental states, from the most sublime virtue or good habit, the deepest Interpersonal relationship, interpersonal affection, to the simplest pleasure. An example of this range of ...

Evolutionary psychology

Evolutionary psychology Evolutionary psychology is a theoretical approach in psychology that examines cognition and behavior from a modern evolutionary perspective. It seeks to identify human psychological adaptations with regards to the ancestral problems they evolv ...

has proposed several explanations for love. 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 disease Sexually transmitted infections (STIs), also referred to as sexually transmitted diseases (STDs) and the older term venereal diseases, are infections that are spread by sexual activity, especially vaginal intercourse, anal sex, and oral ...

s may cause, among other effects, permanently reduced

fertility Fertility is the capability to produce offspring through reproduction following the onset of sexual maturity. The fertility rate is the average number of children born by a female during her lifetime and is quantified demographically. Fertili ...

, injury to the fetus, and increase risks during

childbirth Childbirth, also known as labour and delivery, is the ending of pregnancy where one or more babies exits the internal environment of the mother via vaginal delivery or caesarean section. In 2019, there were about 140.11 million births globall ...

. This would favor exclusive long-term relationships reducing the risk of contracting an STD. 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. 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. Miller described evolutionary psychology as a starting place for further research: "Cognitive neuroscience could try to localize courtship adaptations in the brain. Most importantly, we need much better observations concerning real-life human courtship, including the measurable aspects of courtship that influence mate choice, the reproductive (or at least sexual) consequences of individual variation in those aspects, and the social-cognitive and emotional mechanisms of falling in love." Since Darwin's time there have been similar speculations about the

evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

of human interest in music also as a potential signaling system for attracting and judging the fitness of potential mates. 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. Biologist

Jeremy Griffith Jeremy Griffith (born 1945) is an Australian biologist and author. He first came to public attention for his attempts to find the Tasmanian tiger. He later became noted for his writings on the human condition and theories about human progress, w ...

defines love as 'unconditional selflessness', suggesting utterly cooperative instincts developed in modern humans' ancestor, ''

Australopithecus ''Australopithecus'' (, ; ) is a genus of early hominins that existed in Africa during the Late Pliocene and Early Pleistocene. The genus ''Homo'' (which includes modern humans) emerged within ''Australopithecus'', as sister to e.g. ''Australopi ...

''. Studies of

bonobo The bonobo (; ''Pan paniscus''), also historically called the pygmy chimpanzee and less often the dwarf chimpanzee or gracile chimpanzee, is an endangered great ape and one of the two species making up the genus '' Pan,'' the other being the comm ...

s (a great ape previously referred to as a pygmy chimpanzee) are frequently cited in support of a cooperative past in humans. Bode and Kushnick undertook a comprehensive review of romantic love from a biological perspective in 2021. 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:

Social psychology

Social psychological approaches to explaining love have been developed to help further explain the psychological components involved in love. One of the more prominent concepts pertaining to love was proposed by Robert J. Sternberg known as the "

Triangular theory of love The triangular theory of love is a theory of love developed by Robert Sternberg. In the context of interpersonal relationships, "the three components of love, according to the triangular theory, are an intimacy component, a passion component, and ...

". Proposed within this theory, love follows a triangular motion, flowing with combinations of different levels within the three sides of the triangle. The three sides are Intimacy, Passion, and Commitment. Within those three sides of the triangle, combinations between two can produce certain types of love and affection. For example, Intimacy plus Passion leads to romantic love while Intimacy plus Commitment leads to compassionate love. The relative amount of love invested is explained by the size and general form of the triangle. Triangular theories do not solely apply to one's own current relationship, they also can be meant for explaining what different levels of intimacy/passion/commitment mean in an imbalanced triangle, or even determine your love triangle for a preference of relationship.

Neurochemistry

The conventional view in

biology Biology is the scientific study of life. It is a natural science with a broad scope but has several unifying themes that tie it together as a single, coherent field. For instance, all organisms are made up of cells that process hereditary i ...

is that there are three major drives in love –

libido Libido (; colloquial: sex drive) is a person's overall sexual drive or desire for sexual activity. Libido is influenced by biological, psychological, and social factors. Biologically, the sex hormones and associated neurotransmitters that act up ...

, attachment, and partner preference. The primary neurochemicals (

neurotransmitters A neurotransmitter is a signaling molecule secreted by a neuron to affect another cell across a synapse. The cell receiving the signal, any main body part or target cell, may be another neuron, but could also be a gland or muscle cell. Neur ...

sex hormones Sex hormones, also known as sex steroids, gonadocorticoids and gonadal steroids, are steroid hormones that interact with vertebrate steroid hormone receptors. The sex hormones include the androgens, estrogens, and progestogens. Their effects are ...

, and

neuropeptides Neuropeptides are chemical messengers made up of small chains of amino acids that are synthesized and released by neurons. Neuropeptides typically bind to G protein-coupled receptors (GPCRs) to modulate neural activity and other tissues like the ...

) that govern these drives are

testosterone Testosterone is the primary sex hormone and anabolic steroid in males. In humans, testosterone plays a key role in the development of Male reproductive system, male reproductive tissues such as testes and prostate, as well as promoting secondar ...

estrogen Estrogen or oestrogen is a category of sex hormone responsible for the development and regulation of the female reproductive system and secondary sex characteristics. There are three major endogenous estrogens that have estrogenic hormonal acti ...

dopamine Dopamine (DA, a contraction of 3,4-dihydroxyphenethylamine) is a neuromodulatory molecule that plays several important roles in cells. It is an organic compound, organic chemical of the catecholamine and phenethylamine families. Dopamine const ...

, and

vasopressin Human vasopressin, also called antidiuretic hormone (ADH), arginine vasopressin (AVP) or argipressin, is a hormone synthesized from the AVP gene as a peptide prohormone in neurons in the hypothalamus, and is converted to AVP. It then travel ...

. Central

dopamine pathways Dopamine (DA, a contraction of 3,4-dihydroxyphenethylamine) is a neuromodulatory molecule that plays several important roles in cells. It is an organic chemical of the catecholamine and phenethylamine families. Dopamine constitutes about 80% o ...

mediate partner preference behavior, while vasopressin in the

ventral pallidum The ventral pallidum (VP) is a structure within the basal ganglia of the brain. It is an output nucleus whose fibres project to thalamic nuclei, such as the ventral anterior nucleus, the ventral lateral nucleus, and the medial dorsal nucleus. The ...

and oxytocin in the

nucleus accumbens The nucleus accumbens (NAc or NAcc; also known as the accumbens nucleus, or formerly as the ''nucleus accumbens septi'', Latin for "nucleus adjacent to the septum") is a region in the basal forebrain rostral to the preoptic area of the hypotha ...

and

paraventricular hypothalamic nucleus The paraventricular nucleus (PVN, PVA, or PVH) is a nucleus in the hypothalamus. Anatomically, it is adjacent to the third ventricle and many of its neurons project to the posterior pituitary. These projecting neurons secrete oxytocin and a smaller ...

mediate partner preference and attachment behaviors. Sex drive is modulated primarily by activity in the

mesolimbic dopamine pathway 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 ventra ...

(

ventral tegmental area The ventral tegmental area (VTA) (tegmentum is Latin for ''covering''), also known as the ventral tegmental area of Tsai, or simply ventral tegmentum, is a group of neurons located close to the midline on the floor of the midbrain. The VTA is the ...

and

Trace amine Trace amines are an endogenous group of trace amine-associated receptor 1 (TAAR1) agonists – and hence, monoaminergic neuromodulators – that are structurally and metabolically related to classical monoamine neurotransmitters. Compared to the ...

s (e.g.,

phenethylamine Phenethylamine (PEA) is an organic compound, natural monoamine alkaloid, and trace amine, which acts as a central nervous system stimulant in humans. In the brain, phenethylamine regulates monoamine neurotransmission by binding to trace amin ...

and

tyramine Tyramine ( ) (also spelled tyramin), also known under several other names, is a naturally occurring trace amine derived from the amino acid tyrosine. Tyramine acts as a catecholamine releasing agent. Notably, it is unable to cross the blood-b ...

) play a critical role in regulating neuronal activity in the dopaminergic pathways of the

central nervous system The central nervous system (CNS) is the part of the nervous system consisting primarily of the brain and spinal cord. The CNS is so named because the brain integrates the received information and coordinates and influences the activity of all par ...

. Testosterone and estrogen contribute to these drives by modulating activity within dopamine pathways. Adequate brain levels of testosterone seem important for both human male and female sexual behavior.

Norepinephrine Norepinephrine (NE), also called noradrenaline (NA) or noradrenalin, is an organic chemical in the catecholamine family that functions in the brain and body as both a hormone and neurotransmitter. The name "noradrenaline" (from Latin '' ad'', ...

and

serotonin Serotonin () or 5-hydroxytryptamine (5-HT) is a monoamine neurotransmitter. Its biological function is complex and multifaceted, modulating mood, cognition, reward, learning, memory, and numerous physiological processes such as vomiting and vas ...

have a less significant, contributing role through their

neuromodulatory Neuromodulation is the physiological process by which a given neuron uses one or more chemicals to regulate diverse populations of neurons. Neuromodulators typically bind to metabotropic, G-protein coupled receptors (GPCRs) to initiate a second ...

effects upon dopamine and oxytocin release in certain pathways. 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. Individuals who have recently fallen in love show higher levels of

cortisol Cortisol is a steroid hormone, in the glucocorticoid class of hormones. When used as a medication, it is known as hydrocortisone. It is produced in many animals, mainly by the ''zona fasciculata'' of the adrenal cortex in the adrenal gland ...

Role of the limbic system

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 is known as the Papez circuit. the Papez circuit highlighted the presence of neuronal pathways between vestibular system and limbic system. The vestibular apparatus is in the inner ear this apparatus coordinates the body balance and movement. this requires extensive neuronal networking. Vestibular stimulation can cause changes in mood and emotion. vestibular stimulation by influencing hypothalamus can impact emotions either independently or as part of the general limbic system networks. These emotions can include extreme passivity, loss of drive/motivation, excessive eating and drinking, and rage and violent behavior. Studies show Romantic Love uses reward and motivation systems to focus on a specific individual. The limbic cortical regions process individual emotion factors. In '' A General Theory of Love,'' three professors of psychiatry from

UCSF The University of California, San Francisco (UCSF) is a public land-grant research university in San Francisco, California. It is part of the University of California system and is dedicated entirely to health science and life science. It condu ...

provide an overview of the scientific theories and findings relating to the role of the

limbic system The limbic system, also known as the paleomammalian cortex, is a set of brain structures located on both sides of the thalamus, immediately beneath the medial temporal lobe of the cerebrum primarily in the forebrain.Schacter, Daniel L. 2012. ''Ps ...

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 Limbic resonance is the idea that the capacity for sharing deep emotional states arises from the limbic system of the brain. These states include the dopamine circuit-promoted feelings of empathic harmony, and the norepinephrine circuit-originate ...

, is a capacity which we share, along with the anatomical characteristics of the limbic areas of the brain, with all other mammals. 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 Harry Frederick Harlow (October 31, 1905 – December 6, 1981) was an American psychologist best known for his maternal-separation, dependency needs, and social isolation experiments on rhesus monkeys, which manifested the importance of caregiv ...

on rhesus monkeys, which first established the biological consequences of isolation.

Brain imaging

Brain scanning techniques such as

functional magnetic resonance imaging Functional magnetic resonance imaging or functional MRI (fMRI) measures brain activity by detecting changes associated with blood flow. This technique relies on the fact that cerebral blood flow and neuronal activation are coupled. When an area o ...

have been used to investigate brain regions that seem to be involved in producing the human experience of love. In 2000, a study led by

Semir Zeki Semir Zeki FMedSci FRS is a British and French neurobiologist who has specialised in studying the primate visual brain and more recently the neural correlates of affective states, such as the experience of love, desire and beauty that are ge ...

and Andreas Bartels of

University College London , mottoeng = Let all come who by merit deserve the most reward , established = , type = Public research university , endowment = £143 million (2020) , budget = ...

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 Instinct is the inherent inclination of a living organism towards a particular complex behaviour, containing both innate (inborn) and learned elements. The simplest example of an instinctive behaviour is a fixed action pattern (FAP), in which a v ...

, and part of the

anterior cingulate cortex In the human brain, the anterior cingulate cortex (ACC) is the frontal part of the cingulate cortex that resembles a "collar" surrounding the frontal part of the corpus callosum. It consists of Brodmann areas 24, 32, and 33. It is involved ...

, which is associated with feelings of euphoria. * 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. 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 The angular gyrus is a region of the brain lying mainly in the posteroinferior region of the parietal lobe, occupying the posterior part of the inferior parietal lobule. It represents the Brodmann area 39. Its significance is in transferring vis ...

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.

Love and motivation

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." Joseph Butler believed the human race was made of six senses instead of five. The sixth sense being empathy. Empathy is what makes humans different from other mammals. Empathy allows humans to experience love and to build bonds. The moral that humans gain from empathy allow them to repair and rebuild bonds based from empathy.

References

External links

The Nature of Love (1958)
-

, ''American Psychologist, 13, 573-685''
Harry Harlow
- A Science Odyssey: People and Experiments

- eScienceCommons: The Science of Love

- HowStuffWorks: How Love Works

- The Age: Your dopamine or mine ? {{Navboxes , title = Articles Related to Love (scientific views) , list = {{Evolutionary psychology {{evolution {{Biology-footer {{Psychology {{Neuroscience {{emotion-footer Interpersonal attraction Sociobiology Love