"I love you." Today, we say these three words — to boyfriends and girlfriends, husbands and wives. But to every person, and to every brain, the phrase means something different.
Selection, naturally
The most fit will survive to reproduce, passing on their genes to the next generation. This, of course, is Darwin's theory of natural selection. An individual pursues the most genetically fit partner to pass on favorable traits to offspring, increasing their chance of reproductive success.
Senior Lecturer in Neuroscience John Stein knows all about selecting favorable mates — he is happily married with children. Having a baby is a major investment, so females need to be choosy. And males have to flaunt their stuff to convince females of their worth — heavy antlers on deer, thick manes on lions and brightly-colored feathers on birds show off physical fitness, Stein said. If a male is smart and fast enough to survive despite showy appendages that take energy to maintain and can draw the attention of predators, he must be a genetically fit mate.
But it is 2011, and with hair gel and a dearth of natural predators, humans function outside of these bounds. Fathers do not hunt for food, and mothers do not fight off tigers. The act of survival simply is not that difficult — most everyone lives to reproductive age. So how do humans choose a mate?
The modern equivalent of antlers, Stein said, are gold chains and Porsches. The courtship process — going on dates and exchanging lavish gifts — is just a man's way of saying, "I can provide for you and our children."
And after the male sows his seeds, he sticks around. Monogamy gives children a survival advantage, Stein said, and since the child shares 50 percent of the father's DNA, "it is a worthwhile investment of your time to help your child survive."
Love — that attachment between father and mother — is biologically advantageous.
Your love is my drug
Being in love feels great. Love is almost like a drug.
This actually makes a lot of sense. Peer into the brain of someone who has recently fallen in love, and you will find activity in the same areas associated with addictive behavior and reward-seeking, said Sean Maldonado '11, a neuroscience concentrator who focuses on love and the brain.
When the reward system is activated, a person is inclined to perform that behavior again. This reinforcement is caused by the hormone oxytocin, also called the "cuddle hormone" because of its association with attachment. Oxytocin is necessary for creating a bond between a mother and her infant and is also known to promote monogamy. This hormone is released after orgasms, creating a feeling of attachment between sexual partners.
The ventral tegmental area — that love and drug-stimulated region — is also linked to higher levels of dopamine. Brain-imaging studies show that viewing pictures of loved ones, compared to viewing pictures of neutral friends, causes a peak in activation in that region.
But while some areas of the brain have increased activity during love, others receive less blood flow. One such area is the amygdala, part of the limbic system, which is associated with emotion, especially fear. The longer a couple is together, Maldonado explained, the more comfortable they are in the relationship.
Brains in love have increased levels of dopamine and norepinephrine, as well as decreased levels of serotonin. Such chemical conditions are curiously similar to the effects of Obsessive Compulsive Disorder and depression on the brain. "For all intents and purposes, the lovesick person is mentally ill," Maldonado said.
Love is in the air
Walking across the Main Green, an array of potential mates is within view. How to tell which one is the one?
Try sniffing them. In a 1995 study published in the proceedings of the Royal Society of London, women smelled the T-shirts of men, ranking each shirt in order of preference. Women chose T-shirts of men whose major histocompatibility complexes — which present foreign invaders to trigger an immune response — were most different from their own. Offspring of two people with dissimilar complex types will have stronger immune systems that are able to detect a more diverse array of bacterial and viral invaders.
Birth control has been shown to throw off a woman's sense of smell. A relationship that begins happily while a woman is taking the pill could turn sour if she chooses to stop.
Men can also pick up on scents. Studies show that men find women who are ovulating more attractive than women who are menstruating.
College Love
Looking for love in the party scene is risky as well. Drugs and alcohol can interfere with brain processes, leading to poor judgment. The euphoric effect of drugs and alcohol can be confused for feelings of affection for a partner, Stein explained.
And yet, despite the challenges of college life, many students have found love at Brown. Over one-third of students reported being in an exclusive relationship in The Herald's Spring 2010 poll. There have been 410 marriages between alums who graduated in the 1980s and 410 between alums who graduated in the 1990s, according to the Brown Alumni Association. There have already been 100 marriages between graduates of the most recent decade.
Many of these couples knew each other while at Brown, but some met at alumni events, said Todd Andrews '83, vice president for alumni relations.
"We see this as a strong indication that Brown is a very romantic place," Andrews said.
That magic feeling
Science can provide explanations for love letters and heartache, but it cannot explain the indescribable, magical feeling of finding the one.
"Humans regularly do things that don't make sense within the realm of biology," Stein said. Many people choose to be celibate, deliberately not perpetuating their genes. Just because two people are a good genetic match does not necessarily mean that they will have a lasting, meaningful relationship.
Philosophical love and scientific love need not be mutually exclusive, Maldonado said. It is difficult to say to someone, you are "just feeling a series of chemicals coursing through you," he said. But "it's important to realize that whatever is going on in your brain is what you're going to be feeling, and how you're feeling is real."
"I think love is the most important thing in the world," he said.
