The story of love as told by hormones

Helen Fisher of Rutgers University broke down love into three stages of neurological responses in her landmark paper, "Lust, Attraction, and Attachment in Mammalian Reproduction."

1. LUST: Lust, sex drive, and libido, are defined as the craving for sexual gratification independent of a desire for a specific person. Lust evolved as a way to motivate individuals to seek sex as well as to be receptive to potential suitors' advances. For humans, sex drive switches on near the end of puberty when testosterone reaches a certain level. Oestrogen also plays a role in spurring human's sex drive.

-Testosterone: Androgens like testosterone have long been associated with sexual arousal. When castrated males are injected with testosterone, their sex drive returns. Women with higher levels of testosterone circulating in the blood have more sexual thoughts, a greater desire for sex, and a higher levels of sexual activity on average.

-Oestrogen: Rising levels of oestrogen hormones, like estrogen, triggers

estrus and sexual behavior in females. These help increase sexual motivations just before women ovulate, when estrogen levels are at their peek, to increase the chance of conception. However, this estrus effect is understated in humans as compared to other mammals and is thought to be connected with the fact that we have sex throughout a female's fertility cycle instead of only when women are fertile.

2. ATTRACTION: Attraction allows humans to focus and concentrate their sexual energy on a suitable partner. Feelings of romantic or passionate love are characterized by euphoria when things are going well, mood swings when they’re not, focused attention, obsessive thinking, and intense craving for the individual. These feelings are driven by high dopamine and norepinephrine levels and low serotonin. Attraction evolved to facilitate mate choice, focusing an individual's mating efforts on a preferred partner. In mammals, attraction is characterized by territory defense, nest building, mutual feeding, grooming, maintenance of close proximity, separation anxiety, shared parental chores, as well as feelings of calm, social comfort, emotional unions. Three main hormones are involved in the attraction phase of love:  adrenaline, dopamine, and serotonin.

-Adrenaline: When first falling for someone, your stress responses are activated, which increases adrenalin and cortisol in your blood stream. This is why many people who are deeply attracted to another person experience sweaty palms, a pounding heart, and a dry mouth.

-Dopamine: The brains of love struck couples are loaded with high levels of dopamine, which is thought to be connected with feelings of desire and reward by triggering bursts of euphoria. In fact, dopamine acts very similar to cocaine. This chemical causes a variety of behavioral effects including more energy, less need for food or sleep, increased attention and pleasure in the small details of a new romance.

-Serotonin: A study out of Pisa, Italy found that the low serotonin levels for couples in a new romance are similar to low serotonin levels of obsessive-compulsive patients. For this reason, some believe the chemical is the reason why new lovers continually pop up in the minds of the newly romanced and why affection can become obsessive.

3. ATTACHMENT: Attachment evolved as a way to aid positive social interactions as well as to maintain these romantic connections long enough for a couple's love to result in healthy offspring. How long this attachment phase is said to last on average is a huge point of contention. The hormones oxytocin and vasopressin both contribute to your level of attachment, adding to the sense of calm, peace, and stability one feels with a long-term partner.

-Oxytocin: Oxytocin is best recognized as the hormone responsible for inducing labor, but more recently it has become known as the cuddle hormone. It is associated with maintaining healthy relationships, whether that be in setting boundaries or helping to mediate emotional experiences. In mammals, oxytocin has been known to produce a variety of behaviors. For rats the hormone facilitates nest building and pup retrieval. In sheep it aids in the acceptance of offspring. In prairie voles, it is involved in the formation of adult pair-bonds. In humans, oxytocin stimulates milk secretion and uterine contractions during childbirth. For men and women, it is also released during orgasms, which is thought to aid in pair bonding. One landmark study found a steady relationship, or relationships, may positively influence oxytocin's responsiveness and effectiveness.  Considering that the hormone is present in high levels during childbirth and nursing, it may also aid in bonding between mother and child.

-Vasopressin: Vasopressin is released post-coitus and is thought to be important in securing a long-term partner. The importance of this hormone in pair bonding was found when scientists studied prairie voles. Like humans these animals have much more sex than is needed for reproduction and they form reasonably stable pair-bonds. When vasopressin was suppressed in male prairie voles, their pair-bond deteriorated immediately. They lost their devotion and did not guard their partner against new suitors. Could it be that Vasopressin also triggers our jealous instincts?

Read more abotu Helen Fisher's research at youramazingbrain.org.uk or read her full journal article originally published in the science journal Human Nature, "Lust, Attraction, and Attachment in Mammalian Reproduction."

Photo from hlifemedia.com

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