Table of Contents

The Biology of Love

For centuries humans have been speaking, singing, writing and talking about love. Many theories have been suggested to explain love ranging from the mystical, the supernatural and the physical. Love has been attributed to the heart, as some of its feelings are sensed in that organ. Modern neurobiological science associates love with the nervous system.

Love is one of the basic motives and emotions which are connected with functions of certain areas of the brain, nervous system and endocrinal system. The nervous networks associated with love have evolved over centuries since the first primates appeared on earth. Our love behaviour has a lot to do with our mammal ancestors.

Let us make it clear that we are here talking about romantic love and not other forms of love such as maternal, paternal or fraternal love. Psychologically, romantic love starts with selecting someone in particular as the object of love, excluding any other person. The lover becomes attached to his loved person and sees him as unique in features, ignoring any possible blemishes evidently seen by others. The lover falls head over heels in love with someone, spending a lot of time and energy for the loved one, who becomes the focus of his attention and occupies his mind.

Lovers are invigorated by enormous energy and over-activity. They are frequently unable to sleep and experience a rush of euphoria and volatility in their mood. They channel all of their energy and set about strongly to win the beloved. The hardships increase their passion in what is known as the Romeo and Juliet effect. The frustration adds to the attachment until the lover becomes dependent on the loving relationship. Lovers order their daily priorities to stay in constant contact with their beloved and feel separation anxiety when they are departed. Most lovers feel strong sympathy with the loved one, many of them says they can sacrifice their lives for the lover's protection. One of the striking features in romantic love is thinking repetitively about the beloved in an obsessive manner. The lover yearns and desires to meet the loved one.

Loving partners have strong sexual attraction accompanied by desire to possess the lover, this passion for emotional attachment aims for sexual union. Lovers resort to the most extraordinary effort to regain their loved ones. Many rejected lovers suffer the deepest sense of abandonment and grief which culminate in feelings of despair and decline in vigour with loss of hope and submissiveness.

Helen Fisher is one of the most famous biologists in the world who has studied the subject of love. She has done a lot of research and published many papers in this area of study. She was born in 1945 and worked at Rutgers University in the United States. Helen Fisher studied romantic relationships for over 30 years and published several books which have been bestsellers in America. In her studies, Helen Fisher believes that love is a biological motive, like hunger and thirst and it has its basis in chemical mechanisms in the brain. She divides experience of love into three stages which sometimes overlap partially: desire, attraction and attachment.

The desire allows the two parties to discover each other. And attraction encourages the lovers to intensify all their energies to prepare for mating and intercourse. Attachment keeps the two together so that they prepare for the newborn child and look after it for many years. They stay together and put up with the burdens of childcare in particular since the male may chose to seek another female as he is always ready for fertilisation.

The first phase of desire is governed by secretion of hormones of masculinity and femininity. This is responsible for the overwhelming sexual desire which prepare the couple for sexual intercourse. This stage doesn't last more than weeks or a few months.

The attraction phase is mainly a stage when the lover focuses all his attention on a particular person and not anyone else. This phase grows out of the desire to possess the person who is loved. During it, there is a commitment to that particular person and not to anyone else in preparation for mating.

Studies in neuroscience show that falling in love is accompanied by secretion of several neurotransmitters in the brain. Neurotransmitters are chemicals that affect the activity of the brain and they include substances such as dopamine, serotonin and noradrenaline. These substances are responsible for the feelings of happiness, euphoria and mental excitement and it is similar to the experience of an addict on amphetamines. Amphetamines affect the centres of pleasure in the brain and some of the side-effects of use of amphetamines include increased heart rate, loss of appetite, increased activity and vitality, lack of sleep and feeling of great alertness and excitement. Studies indicate that this stage may last for a year or more and sometimes for up to 3 years.

Because the stages of desire and attraction are temporary by nature they must be supplemented by another stage which will strengthen the relationship and make it longer term. This is the stage of attachment which makes the couple increasingly closer and builds a sense of the relationship which is stronger so that it would last for several years or even decades.

Scientists have found that several hormones in the body increases at the stage of attachment such as the hormone oxytocin and vasopressin. Those hormones help to form a stronger relationship of interdependence and union between the couple which would last long enough to allow for the care of the newborn. In a study by the Italian scientist Enzo Immanuel the hormone responsible for the growth of brain cells (NGF or nerve growth factor) was found to have the highest level when the individual is in a state of love and only return to its normal levels after one year. This proved that love increase the vitality of the mind as well as body and makes the body more able to resist disease.

In her book, “Why Do We Love? Nature and Chemistry of Romantic Love” Helen Fisher explains her theory for the evolution of three systems which are developed in the brain primarily to achieve the right circumstances for the human beings to breed and multiply.

The first stage is the stage of sexual desire which motivate humans to seek mating with the opposite sex. The second is attachment to the other which appears in the early stage of romantic love and makes the relationship deeper and more intense. The third stage is the stage of emotional attachment which includes the feelings of deep union between the person and his partner and helps to unite them for a long term. Love may begin with any of the three stages. Some people may have sex with someone for the first time and then they fall in love with him or her. Others may feel intense emotions and attraction to another person which develops into a romantic love and later the sexual desire become more evident. However, while the sex drive has evolved for mating with more than one partner, the romantic love has evolved to focus energy on mating with one particular partner in any given time. The attachment has evolved to enable us to form a lasting partnership so that we may be able to raise our descendants together with a partner, working hand-in-hand to reared them.

Dr Fisher says that the basic feelings in romantic love includes such things as the beloved taking a special meaning for the lover. Most lovers can identify things that do not appeal to them in the beloved but they put it aside and focus all their attention on adoring features in the beloved. There are certain sensations and feelings which are characteristic of romantic love such as feelings of joy, fluctuations in mood, feeling of immense energy, a desire to possess the beloved and fear of separation from him or her. In addition, there are also some physical sensations such as increase in heart beat, difficulty in breathing and longing for seeing the beloved. The beloved may become an obsession, its image and features persistently coming to the mind of the lover in a similar way to someone with obsessive disorder.

Helen Fisher studied 49 men and women to find out which neural circuits in the brain are responsible for romantic love. The subjects of the research consisted of 17 people who have fallen madly in love a short while ago and 17 who are still in a state of love and 17 who have been deserted by their loved ones. The most important idea she put forward is that romantic love is stronger than the sex drive. You wouldn’t expect someone to suffer depression, commit suicide or kill someone else if his offer for having sex was rejected, however; every day everywhere in the world, a lot of people suffer the most horrible and painful feelings and may even act in the most insane way because their offer of love was rejected. Dr Fisher suggests that some antidepressants can actually diminish the feelings of romantic love and emotional attachment as well as the sex drive.

Both men and women take physical attractiveness as one of the factors in choice of the future partner. However, men appreciate the value of the attractiveness more than women. In a study published by Rutgers University, Helen Fisher the evolutionary anthropologist showed that there are differences in the MRI images between men and women who are in the early stages of falling in love. Men showed activity in two regions in the brain, the first area is responsible for the integration between visual stimuli and other sensations and the second area is related to the erection of the penis. On the contrary, the study showed that the most active regions of the brain of women in the early stages of love are areas associated with recall of memories. The study concludes there is an evolutionary basis which make women need to identify the man who shows in his behaviour repeated evidence that he would help to raise the offspring with the female.

In another study published in the 2006, Helen Fisher reported that the Magnetic Resonance Imaging in people living an intense and overwhelming love experience have certain areas in the brain which are more active than others. The first area is the Caudate Nucleus, and the second is Ventral Tegmental Area.

Studies have proved that the characteristics of romantic love are not considerably different between different ages, sex, and ethnic group or even among homosexuals. When they applied a questionnaire to test the feelings and reactions of people in love there was no significant differences between those who are over 50 and those who are under 25 in 82% of cases. In 87% of cases the responses of men and women were identical. The homosexuals and heterosexuals had similar responses in 86% of cases. The responses of 82% of whites and other races were also similar.

In poetry, myths and legends as well as in many anthropological and psychological studies; romantic love is emphasised as a universal human phenomenon. It is one of the emotional and motivational systems in both birds and mammals which have evolved to guide their reproductive and mating activity and to help promote their responsibility for upbringing of offsprings. The other two systems are sex drive and emotional attachment.

Each system is associated with a number of feelings and behavioural patterns which are connected to a number of neuronal networks. Each of these has evolved to guide some aspect of reproduction. Each system interacts with the other two in combinations of countless ways to generate a wide range of emotions, behaviour and motivations.

The three systems of love: desire attraction and attachment ##

The sex drive is characterised by a tendency to seek gratification by mating with multiple partners. The sex drive is associated in mammals with the hormones androgens and oestrogens. In humans, the hormone testosterone plays a principal part in sexual desire in men and women alike. Studies using Magnetic Resonance shows that sexual excitement in man is associated with activities in certain neuronal networks including the hypothalamus and amygdala.

Attraction appears in the form of increased activity and focusing the attention on the partner selected. This behaviour also includes obsessional following, defensive gestures and signs to indicate the connection and protection of the partner. Attraction phase involves rushing to win the partner and possessive behaviour. Our modern knowledge shows that the neuronal network connected with attraction is associated with the activity of dopamine brain pathways involved in reward of behaviour. Most probably, the central Nor-epinephrine activity is also increased while the activity of Serotonin is reduced in this neuronal mechanism. There are other neuronal mechanisms which work together to produce a range of emotions, motivations, perceptions and behaviour commonly seen in romantic behaviour.

In birds and mammals, attraction is characterised by defending territory and building nest and offering food for the partner. Other behaviours seen in attraction are caring for the body of the partner, keeping close to it, fear of being distant from the partner and taking part in paternal responsibility and amicable behaviour. In man, attraction takes the form of love and companionship. The human behaviour during the phase of attraction phase is similar to what is mentioned above, in addition to calmness, sense of security, social comfort, emotional union with the partner and companion in the long term.

Studies suggest that the neuronal system associated with attraction is based on oxytocin and vasopressin in the nucleus accumbens, which is a group of nerve cells known to play an important part in addiction and habituation on pleasure producing behaviour.

All these basic brain systems have developed to play different roles in the process of courtship, mating, reproduction and paternal care. The sex drive have developed to motivate our ancestors to seek copulation was multiple suitable partners. However attraction and its developed human form, romantic love, appeared to motivate the individual to choose among potential partners only one which is more suitable and focusing the individuals attention on the most preferred partner for reproduction. In this way the individual conserves its energy and time in the process of mating.

Attachment has developed to keep a relationship with a partner long enough for reproduction and to allow for completion of paternal duties according to the needs of the species. In addition, the three neuronal systems interact in different forms to direct a multitude of emotions, behaviours and motivations connected with human reproduction.

In a study by Helen Fisher and Lucy Brown (a researcher in Albert Einstein College of medicine) with others, they used Functional Magnetic Resonance on a number of women and men who have been through an intense love experience for few months. There was evidence of increased activity in the dorsal part of the caudate nucleus and the right ventral part of the Pallidum. This was confirmed by another study in London University College by Andreas Bartels and Samir zaki from the Department of Cognitive Neurology. It is known that the Pallidum produces and distributes dopamine on different brain areas including the caudate nucleus. Pallidum plays an important part in the reward mechanism in the human brain. This area of the brain is connected with the neuronal network responsible for the sense of pleasure, general excitement, focusing attention, defensiveness, seeking reward and obtaining it. The caudate nucleus is connected with defensiveness and guided behaviour.

Such information indicates that focusing attention, defensiveness and guided behaviour which characterise romantic love is related to the increased central dopamine activity in the brain. The characteristic function of the dopamine is its relationship to the sense of euphoria, increased energy, sleeplessness, mood swings, emotional dependency and longing; which are all features of the romantic love. It is highly probable that dopamine contributes to the appearance of such aspects of the romantic love behaviour.

On the other hand, the increase in production of norepinephrine or noradrenaline play a role in the love behaviour as it is responsible for such features as increase in heart beats and other physiological manifestations of love. There is also evidence that the low levels of serotonin in the blood in lovers are similar to the low level of serotonin in patients with obsessive-compulsive disorder. Probably the low level of serotonin in the brain and blood is responsible for obsessional preoccupation with the loved person as well as impulsiveness.


  • Andreas Bartels and Semir Zeki (2000)."The neural basis of romantic love".Neuroreport,Nov 27;11(17):3829-34.
  • Emanuele, E.; Polliti, P.; Bianchi, M.; Minoretti, P.; Bertona, M.; & Geroldi, D (2005). "Raised plasma nerve growth factor levels associated with early-stage romantic love". Psychoneuroendocrinology Sept. 05.
  • Fromm, Eric; "The Art of Loving", Harper Perennial (September 5, 2000), Original English Version, ISBN 978-0060958282
  • Helen Fisher (2004). "WHY WE LOVE: The Nature and Chemistry of Romantic Love Why We Love: The Nature and Chemistry of Romantic Love". Publisher Henry Holt, 2004.
  • Fisher, H, A Aron and LL Brown (2006)."Romantic Love: A Mammalian Brain System for Mate Choice".
  • H. Fisher, A Aron and LL Brown (2005) Romantic Love: An fMRI study of a neural mechanism for mate choice. Journal of Comparative Neurology, 493:58-62.
  • “The Neurobiology of Social Recognition, Attraction and Bonding," Keith Kendrick (Ed), Philosophical Transactions of the Royal Society: Biological Sciences. 361:2173-2186

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