Why we love — the actual chemistry

there is a book on this called “Why We Love” by helen fisher. see “First flush of love not emotional”

It’s based on research/experiments with hundreds of subjects over several years involving psychological surveys, fMRI, blood tests, and the like. Also seems this applies to mammals of all sorts. Fun to read all the way through.

  1. Three stages (lust, love, attachment)
  2. Lust is characterized by sexual attraction to the opposite sex, and driven primarily by testosterone regardless of gender
  3. Love is defined by focus/obsession with one mate in particular, mediated by dopamine and norephrenine. when the “mate” is not present the rise in dopamine/norephrenine causes a drop in serotonin, just like an addiction/depression.
  4. Attachment is creates the sense of peace/solace/trust in a long term relationship and occurs primarily due to oxytocin in females and vasopressin in males.

According to the book there are interactions between these three effects (for example attachment may suppress lust), with evolutionary explanations.

Neuroeconomic research shows that expressions of “trust” increase oxytocin in people (men & women), while expressions of mistrust create a rise in testosterone only in men (not women).

Update on 9/2/2008: “‘Bonding Gene’ Could Help Men Stay Married”

A study of Swedish twin brothers found that differences in a gene modulating the hormone vasopressin were strongly tied to how well each man fared in marriage.

“Our main finding was an association between a variant of the vasopressin receptor 1a gene and how strong bonds men reported they had to their partners,” said lead researcher Hasse Walum, of the department of medical epidemiology and biostatistics at the Karolinska Institute in Stockholm. “Men carrying this variant scored on average lower on a scale measuring the strength of the bond compared to men not carrying this variant.”

Women married to men carrying the “poorer bonding” form of the gene also reported “lower scores on levels of marital quality than women married to men not carrying this variant,” Walum noted.

Vasopressin activates the brain’s reward system, and “you could say that mating-induced vasopressin release motivates male voles to interact with females they have mated with,” Walum said. “This is not a sexual motivation, but rather a sort of prolonged social motivation.” In other words, the more vasopressin in the brain, the more male voles want to stick around and mingle with the female after copulation is through. This effect “is more pronounced in the monogamous voles,” Walum noted.

They found that men with a certain variant, known as an allele, of the vasopressin 1a gene, called 334, tended to score especially low on a standard psychological test called the Partner Bonding Scale. They were also less likely to be married than men carrying another form of the gene. And carrying two copies of the 334 allele doubled the odds that the men had undergone some sort of marital crisis (for example, the threat of divorce) over the past year.

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