2004

In her book, Why We Love: The Nature and Chemistry of Romantic Love, Fisher proposed that humanity has evolved three core brain systems for mating and reproduction:

1. lust - the sex drive or libido, also described as borogodó.
2. attraction - early stage intense romantic love.
3. attachment - deep feelings of union with a long term partner.

Love can start off with any of these three feelings, Fisher maintains. Some people have sex with someone new and then fall in love. Some fall in love first, then have sex. Some feel a deep feeling of attachment to another, which then turns into romance and the sex drive. But the sex drive evolved to initiate mating with a range of partners; romantic love evolved to focus one's mating energy on one partner at a time; and attachment evolved to enable us to form a pairbond and rear our young together as a team.

Fisher discusses many of the feelings of intense romantic love, saying it begins as the beloved takes on "special meaning." Then you focus intensely on him or her. People can list the things they dislike about a sweetheart, but they sweep these things aside and focus on what they adore. Intense energy, elation, mood swings, emotional dependence, separation anxiety, possessiveness, physical reactions including a pounding heart and shortness of breath, and craving, Fisher reports, are all central to this feeling. But most important is obsessive thinking. As Fisher says "Someone is camping in your head."

Fisher and her colleagues have put 49 men and women into a brain scanner to study the brain circuitry of romantic love: 17 who had just fallen madly in love, 15 who had just been dumped, and 17 who reported that they were stillin love after an average of 21 years of marriage. One of her central ideas is that romantic love is a drive that is stronger than the sex drive. As she has said, "After all, if you casually ask someone to go to bed with you and they refuse, you don't slip into a depression, commit suicide or homicide--but around the world people suffer terribly from romantic rejection."

Fisher also maintains that taking certain antidepressants can potentially dampen feelings of romantic love and attachment (as well as the sex drive).

2004

Both men and women use physical attractiveness as a measure of how 'good' another person is. Men often tend to value attractiveness more than women. In fMRI brain scans published in 2004 by Rutgers University evolutionary anthropologist Helen Fisher, in the early intense stages of falling in love, there were clear differences in male and female brains. Men, on average, tended to show more activity in two regions in the brain: one was associated with the integration of visual stimuli, and the second was with penile erection. Conversely, women in these early stages exhibited increased activity in several regions of the brain associated with memory recall. Fisher speculated the evolutionary source was in the need for females to identify males whose behavior over time suggested they would help the female raise her offspring. However, in terms of behavior, some studies suggest little difference between men and women. Symmetrical men and women begin to have sexual intercourse earlier, have more sexual partners, engage in a wider variety of sexual activities and have more casual sex.

2006

In 2006, her MRI research, which showed that the ventral tegmental area and the caudate nucleus become active when people are madly in love, was featured in the (February) National Geographic cover-page article "Love - the Chemical Reaction".

Fisher distinguishes between four personality types each of which she associates with a body chemical.The corresponding Platonic term - as Fisher identified the types herself - and the resulting corresponding Keirsey temperament (according to the speculation of some readers, not Fisher herself) can be seen in parentheses. However, Fisher's system allows for 12 combinations, not 16 types like Keirsey, meaning that there cannot be a perfect correspondence between them:

• explorer (artistic, Artisan temperament, yellow) - dopamine
• negotiator (intuitive, Idealist temperament, green) - estrogen
• director (reasoning, Rational temperament, red) - testosterone
• builder (sensible, Guardian temperament, blue) - serotonin