Love (scientific views) - AbsoluteAstronomy.com

The theory of a biological basis of love
Love
Love is an emotion of strong affection and personal attachment. In philosophical context, love is a virtue representing all of human kindness, compassion, and affection. Love is central to many religions, as in the Christian phrase, "God is love" or Agape in the Canonical gospels...

has been explored by such biological

Biology

Biology is a natural science concerned with the study of life and living organisms, including their structure, function, growth, origin, evolution, distribution, and taxonomy. Biology is a vast subject containing many subdivisions, topics, and disciplines...

sciences as evolutionary psychology

Evolutionary psychology

Evolutionary psychology is an approach in the social and natural sciences that examines psychological traits such as memory, perception, and language from a modern evolutionary perspective. It seeks to identify which human psychological traits are evolved adaptations, that is, the functional...

, evolutionary biology, anthropology

Anthropology

Anthropology is the study of humanity. It has origins in the humanities, the natural sciences, and the social sciences. The term "anthropology" is from the Greek anthrōpos , "man", understood to mean mankind or humanity, and -logia , "discourse" or "study", and was first used in 1501 by German...

and neuroscience

Neuroscience

Neuroscience is the scientific study of the nervous system. Traditionally, neuroscience has been seen as a branch of biology. However, it is currently an interdisciplinary science that collaborates with other fields such as chemistry, computer science, engineering, linguistics, mathematics,...

. Specific chemical substances such as oxytocin

Oxytocin

Oxytocin is a mammalian hormone that acts primarily as a neuromodulator in the brain.Oxytocin is best known for its roles in sexual reproduction, in particular during and after childbirth...

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

Evolutionary psychology

have proposed several explanations for love. Human infants and children are for a very long time dependent on parental help. Love have therefore been seen as mechanism to promote mutual parental support of children for an extended time period. Another is that sexually transmitted disease

Sexually transmitted disease

Sexually transmitted disease , also known as a sexually transmitted infection or venereal disease , is an illness that has a significant probability of transmission between humans by means of human sexual behavior, including vaginal intercourse, oral sex, and anal sex...

s may cause, among other effects, permanently reduced fertility

Fertility

Fertility is the natural capability of producing offsprings. As a measure, "fertility rate" is the number of children born per couple, person or population. Fertility differs from fecundity, which is defined as the potential for reproduction...

, injury to the fetus, and increase risks during childbirth

Childbirth

Childbirth is the culmination of a human pregnancy or gestation period with the birth of one or more newborn infants from a woman's uterus...

. This would favor exclusive long-term relationships reducing the risk of contracting a 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

The Descent of Man, and Selection in Relation to Sex

The Descent of Man, and Selection in Relation to Sex is a book on evolutionary theory by English naturalist Charles Darwin, first published in 1871. It was Darwin's second great book on evolutionary theory, following his 1859 work, On The Origin of Species. In The Descent of Man, Darwin applies...

time there have been similar speculations about the evolution

Evolution

Evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organisation, including species, individual organisms and molecules such as DNA and proteins.Life on Earth...

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.

Neurochemistry

Studies in neuroscience

Neuroscience

have involved chemicals that are present in the brain and might be involved when people experience love. These chemicals include: nerve growth factor

Nerve growth factor

Nerve growth factor is a small secreted protein that is important for the growth, maintenance, and survival of certain target neurons . It also functions as a signaling molecule. It is perhaps the prototypical growth factor, in that it is one of the first to be described...

, testosterone

Testosterone

Testosterone is a steroid hormone from the androgen group and is found in mammals, reptiles, birds, and other vertebrates. In mammals, testosterone is primarily secreted in the testes of males and the ovaries of females, although small amounts are also secreted by the adrenal glands...

, estrogen

Estrogen

Estrogens , oestrogens , or œstrogens, are a group of compounds named for their importance in the estrous cycle of humans and other animals. They are the primary female sex hormones. Natural estrogens are steroid hormones, while some synthetic ones are non-steroidal...

, dopamine

Dopamine

Dopamine is a catecholamine neurotransmitter present in a wide variety of animals, including both vertebrates and invertebrates. In the brain, this substituted phenethylamine functions as a neurotransmitter, activating the five known types of dopamine receptors—D1, D2, D3, D4, and D5—and their...

, norepinephrine

Norepinephrine

Norepinephrine is the US name for noradrenaline , a catecholamine with multiple roles including as a hormone and a neurotransmitter...

, serotonin

Serotonin

Serotonin or 5-hydroxytryptamine is a monoamine neurotransmitter. Biochemically derived from tryptophan, serotonin is primarily found in the gastrointestinal tract, platelets, and in the central nervous system of animals including humans...

, oxytocin

Oxytocin

Oxytocin is a mammalian hormone that acts primarily as a neuromodulator in the brain.Oxytocin is best known for its roles in sexual reproduction, in particular during and after childbirth...

, and vasopressin

Vasopressin

Arginine vasopressin , also known as vasopressin, argipressin or antidiuretic hormone , is a neurohypophysial hormone found in most mammals, including humans. Vasopressin is a peptide hormone that controls the reabsorption of molecules in the tubules of the kidneys by affecting the tissue's...

. Adequate brain levels of testosterone seem important for both human male and female sexual behavior. Dopamine, norepinephrine, and serotonin are more commonly found during the attraction phase of a relationship. Oxytocin and vasopressin seemed to be more closely linked to long term bonding and relationships characterized by strong attachments.

The conventional view in biology

Biology

is that there are two major drives in love — sexual attraction

Sexual attraction

Sexual attractiveness or sex appeal refers to an individual's ability to attract the sexual or erotic interest of another person, 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...

and attachment

Attachment theory

Attachment theory describes the dynamics of long-term relationships between humans. Its most important tenet is that an infant needs to develop a relationship with at least one primary caregiver for social and emotional development to occur normally. Attachment theory is an interdisciplinary study...

. Attachment between adults is presumed to work on the same principles that lead an infant to become attached to his or her mother or father– or both.

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.

Anthropologist Helen Fisher

Helen Fisher (anthropologist)

Helen E. Fisher is a Canadian-American anthropologist and human behavior researcher. She is professor at Rutgers University. Fisher has studied romantic interpersonal attraction for over 30 years. Prior to becoming a research professor at Rutgers University, she was a research associate at the...

also adds lust to the experience of love. Lust exposes people to others, and is the initial passionate sexual desire that promotes mating

Mating

In biology, mating is the pairing of opposite-sex or hermaphroditic organisms for copulation. In social animals, it also includes the raising of their offspring. Copulation is the union of the sex organs of two sexually reproducing animals for insemination and subsequent internal fertilization...

, and involves the increased release of chemicals such as testosterone

Testosterone

and estrogen

Estrogen

. These effects rarely last more than a few weeks or months.

Serotonin

Chemically, the serotonin effects of being infatuated have a similar chemical appearance to obsessive-compulsive disorder

Obsessive-compulsive disorder

Obsessive–compulsive disorder is an anxiety disorder characterized by intrusive thoughts that produce uneasiness, apprehension, fear, or worry, by repetitive behaviors aimed at reducing the associated anxiety, or by a combination of such obsessions and compulsions...

; which could explain why people experiencing infatuation cannot think of anyone else. For this reason some assert that taking SSRI

Selective serotonin reuptake inhibitor

Selective serotonin re-uptake inhibitors or serotonin-specific reuptake inhibitor are a class of compounds typically used as antidepressants in the treatment of depression, anxiety disorders, and some personality disorders. The efficacy of SSRIs is disputed...

s and other antidepressants impede one's ability to fall in love. In one particular case anthropologist Helen Fisher noted:

Oxytocin

Nerve growth factor

In 2005, Italian scientists at Pavia University found that a protein molecule known as the nerve growth factor

Nerve growth factor

(NGF) has high levels when people first fall in love, but these return to previous levels after one year. Specifically, four neurotrophin

Neurotrophin

Neurotrophins are a family of proteins that induce the survival, development, and function of neurons.They belong to a class of growth factors, secreted proteins that are capable of signaling particular cells to survive, differentiate, or grow. Growth factors such as neurotrophins that promote the...

levels (NGF, BDNF, NT-3, and NT-4

NT-4

Neurotrophin-4 , also known as neurotrophin-5 , is a protein that in humans is encoded by the NTF4 gene.NT-4 is a neurotrophic factor that signals predominantly through the TrkB receptor tyrosine kinase....

) of 58 subjects who had recently fallen in love were compared with levels in two control groups who were either single or already engaged in a long-term relationship. The results showed that NGF levels were significantly higher in the subjects in love than as compared to either of the control groups.

Role of the limbic system

In A General Theory of Love
A General Theory of Love
A General Theory of Love is a book about the science of human emotions and biological psychiatry written by Thomas Lewis, Fari Amini and Richard Lannon, psychiatry professors at the University of California, San Francisco, and first published by Random House in 2000...

, three professors of psychiatry from UCSF provide an overview of the scientific theories and findings relating to the role of the limbic system

Limbic system

The limbic system is a set of brain structures including the hippocampus, amygdala, anterior thalamic nuclei, septum, limbic cortex and fornix, which seemingly support a variety of functions including emotion, behavior, long term memory, and olfaction. The term "limbic" comes from the Latin...

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

Limbic resonance is the capacity for sharing deep emotional states arising from the limbic system of the brain. These states include the dopamine circuit promoted feelings of empathic harmony, and the norepinephrine circuit originated emotional states of fear, anxiety and anger. The concept was...

, 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 Harlow

Harry Frederick Harlow was an American psychologist best known for his maternal-separation and social isolation experiments on rhesus monkeys, which demonstrated the importance of care-giving and companionship in social and cognitive development...

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

Brain imaging

Brain scanning techniques such as magnetic resonance imaging

Magnetic resonance imaging

Magnetic resonance imaging , nuclear magnetic resonance imaging , or magnetic resonance tomography is a medical imaging technique used in radiology to visualize detailed internal structures...

have been used to investigate brain regions that seem to be involved in producing the human experience of love.

External links

The Nature of Love (1958) - Harry Harlow
Harry Harlow
Harry Frederick Harlow was an American psychologist best known for his maternal-separation and social isolation experiments on rhesus monkeys, which demonstrated the importance of care-giving and companionship in social and cognitive development...

, American Psychologist, 13, 573-685
Harry Harlow - A Science Odyssey: People and Experiments
http://esciencecommons.blogspot.com/2009/10/science-of-love.html - eScienceCommons: The Science of Love
http://people.howstuffworks.com/love6.htm - HowStuffWorks: How Love Works
http://www.theage.com.au/news/General/Your-dopamine-or-mine/2005/06/03/1117568370393.html - The Age: Your dopamine or mine ?

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