Love. It is a powerful human emotion, the driving force behind many of our decision, and (according to Albus Dumbledore) the one thing that Voldemort cannot understand. However, many people do not understand how this phenomenon occurs. Love is, in fact, driving by different chemical and hormonal changes in the brain.
Love is generally broken up into three stages: lust, attraction, and attachment.
1. Lust
Lust is the initial attraction between two people, based solely on hormones, specifically estrogen and testosterone. Testosterone can be present in both men and women and is a large factor in the sex drive, hence this is the section of attraction that (evolutionarily) primarily concerned procreation. This section tends to last for a few weeks to a few months, depending on the person in question.
2. Attraction
Attraction is the phase generally considered to be "love." This phase causes one to focus more on their significant other and on romance. Throughout this period the brain releases a variety of chemicals which affect one's mood, commonly called monoamines. These include, but are not limited to, the following: pheromones, serotonine, dopamine, and norepinephrine. There is also a sudden spike in the presence of NGH (Nerve Growth Hormone) which eventually returns to the typical level. Scientists believe that these chemicals affect the brain in a way similar to amphetamines. The area of the brain involved with pleasure is stimulated, and the affected party often experiences increased heart rate, insomnia, decreased appetite, and feelings of excitement. They are often totally absorbed with thoughts of their significant other. This stage is believed to last from one and a half to three years.
3. Attachement
Unlike the other two stages, which are temporary, attachement is the phase of love concerned with love term and marital relationships. Attachement increases and strengthens the bonds between people, allowing for connections that can last years or even decades. Attachement is typically caused by shared traits - children, houses, and common interests, to name a few. Attachement is usually associated with an increase in the presence of oxytocin and vasopressin. This stage will last for the remainder of the relationship.
Explanation of various neurochemicals:
Estrogen
Estrogen is a group of chemically similar compounds including estrone, estradoil, and estriol. The two main sex hormones, estrogen and testosterone, are found in both men and women, however, estrogen is more prevalent in women. It allows for the menstrual cycle to occur and allows for women to bear children. Estrogen can help women retain fluid and even reduce the risk of breast cancer.
Testosterone
Testosterone is the primary sex hormone in men, although it is also present in small amounts in women. (The hormone is approximately ten times more present in men than in women.) Testosterone allows for the development of the testis and prostate. Furthermore it increases muscle mass, bone mass, and growth of hair on the body.
Pheromones
Pheromones are various chemicals that both humans and animals excrete in response to various social situations. They are excreted when the being in question is aggregated or alarmed. Some are used as a way of attracting partners of another gender, as neurotransmitter signals, as a developmental trigger, as markings of territory, to transfer information about an animal's history, and to mark a trail for other members of the species. They are also help activate the sex drive in humans and animals.
Serotonine
Serotonine is also a neurotransmitter. It affects moods and mental functions, movement abilities, the ability of the body to regulate temperature and blood pressure, the ability to vomit, the ability to sleep, and the lessening of depression. Certain foods can affect the amount of serotonine in the body, and therefore have an impact on one's ability to sleep.
Dopamine
Dopamine is yet another neurotransmitter. It has similar affects on the body as adrenaline, impacting motor skills, feelings, and ability to feel enjoyment or pain.
Norepinephrine
Norepinephrine is a hormone and a neurotransmitter. When it acts as a hormone is activates the phenomenon commonly referred to as "fight or flight" which helps the body deal with times of disaster. When it acts as a neurotransmitter it helps send nerve signals between neurons.
Oxytocin
Oxytocin, a neuromodulator, plays a big part for women in human reproduction. It allows them to give birth and breastfeed their children. It also has an effect in relationships, enabling recognition, bonding between two individuals, and increases feelings of motherhood and anxiety. People who are lacking in oxytocin may be sociopaths, psychotic, self-obsessed, and manipulative.
Vasopressin
Although vasopressin's main function is in homeostasis (see blog post on sharks), it also facilitates social interaction and bonding.
Check out a cute song about the science of love
here.
Sources:
http://www.bbc.co.uk/science/hottopics/love/
http://en.wikipedia.org/wiki/Biological_basis_of_love
http://www.scientificamerican.com/article.cfm?id=your-brain-in-love-graphsci
http://en.wikipedia.org/wiki/Love#Biological_basis
http://www.wisegeek.com/what-is-estrogen.htm
http://en.wikipedia.org/wiki/Testosterone
http://en.wikipedia.org/wiki/Pheromone
http://www.whatisserotonin.com/what-is-serotonin/what-is-serotonin/
http://bipolar.about.com/od/glossary/g/gl_norepinephri.htm
http://en.wikipedia.org/wiki/Oxytocin
http://en.wikipedia.org/wiki/Vasopressin
Researchers created an experiment in which brewer's yeast was fed sugar and encouraged to reproduce, in hopes that the typically unicellular organism would perhaps create some kind of multicellular creature. To encourage this evolution the scientists raised so called "lines of yeast" from a single cell in 10 individual flasks full of "broth" - a soupy substance of nutrients. The flasks were shaken constantly for twenty four hours, and then allowed to settle. One drop of settled cells were put into a new flask and the yeast grew again. This meant that if the yeast fell quickly it would have a larger chance of survival. In a few weeks Dr. Ratcliff, the leader of the study, found that the yeast cells fell rapidly and created a small cloud of yeast at the base of the container. When examined under a microscope, it appeared that the yeast was, in fact, growing in small colonies. Each of these contained hundreds of individual cells. These colonies appeared to be in the shape of snowflakes, and appeared after a mere 60 generations of cells.
