THE MOLECULE OF MOREidealized, curious, future looking. The later part, companionate love, is
H&N focused—satisfying, peaceful, and experienced through bodily
senses and emotions.
A romance built on dopamine is a thrilling, if short-lived, roller
coaster ride, but our brain chemistry gives us the tools to move down the
path that leads to companionate love. Just as dopamine is the molecule
of obsessive yearning, the chemicals most associated with long-term
relationships are oxytocin and vasopressin. Oxytocin is more active in
women and vasopressin in men.
Scientists have studied these neurotransmitters in the laboratory
in a variety of animals. For example, when scientists injected oxytocin
into the brains of female prairie voles, the animals formed a long-term
bond with whatever male happened to be around. Similarly, when male
voles that were genetically programmed to be promiscuous were given
a gene that boosted vasopressin, they mated with one female exclu-
sively, even though other receptive females were available. Vasopressin
acted like a “good-husband hormone.” Dopamine does the opposite.
Human beings who have genes that produce high levels of dopamine
have the highest number of sexual partners and the lowest age of first
sexual intercourse.
Most couples have sex less frequently as obsessive dopaminergic
love evolves into companionate H&N love. This makes sense, since oxy-
tocin and vasopressin suppress the release of testosterone. In a similar
way, testosterone suppresses the release of oxytocin and vasopressin,
which helps explain why men with naturally high quantities of testos-
terone in their blood are less likely to marry. Similarly, single men have
more testosterone than married men. And if a man’s marriage becomes
unstable, his vasopressin falls, and his testosterone goes up.
Do human beings require long-term companionship? There’s good
evidence that the answer is yes. Despite the superficial appeal of hav-
ing multiple partners, most people eventually settle down. A United
Nations survey found that more than 90 percent of men and women
marry by the age of forty-nine. We can live without companionate love,
but the majority of us arrange a good portion of our lives around trying
to find it and keep it. The H&Ns give us the ability to do that. They