This week's Economist has an article on the chemistry of love and relationships (at least in voles.) For those of you who do not have a subsciption - and I recommend that you get one - here is the article for your enjoyment and reflection:
I GET A KICK OUT OF YOU
Feb 12th 2004
Scientists are finding that, after all, love really is down to a chemical
addiction between people
OVER the course of history it has been artists, poets and playwrights who
have made the greatest progress in humanity's understanding of love. Romance has
seemed as inexplicable as the beauty of a rainbow. But these days scientists are
challenging that notion, and they have rather a lot to say about how and why
people love each other.
Is this useful? The scientists think so. For a start, understanding the
neurochemical pathways that regulate social attachments may help to deal with
defects in people's ability to form relationships. All relationships, whether
they are those of parents with their children, spouses with their partners, or
workers with their colleagues, rely on an ability to create and maintain social
ties. Defects can be disabling, and become apparent as disorders such as autism
and schizophrenia--and, indeed, as the serious depression that can result from
rejection in love. Research is also shedding light on some of the more extreme
forms of sexual behaviour. And, controversially, some utopian fringe groups see
such work as the doorway to a future where love is guaranteed because it will be
provided chemically, or even genetically engineered from conception.
The scientific tale of love begins innocently enough, with voles. The prairie
vole is a sociable creature, one of the only 3% of mammal species that appear to
form monogamous relationships. Mating between prairie voles is a tremendous
24-hour effort. After this, they bond for life. They prefer to spend time with
each other, groom each other for hours on end and nest together. They avoid
meeting other potential mates. The male becomes an aggressive guard of the
female. And when their pups are born, they become affectionate and attentive
parents. However, another vole, a close relative called the montane vole, has no
interest in partnership beyond one-night-stand sex. What is intriguing is that
these vast differences in behaviour are the result of a mere handful of genes.
The two vole species are more than 99% alike, genetically.
WHY DO VOLES FALL IN LOVE?
The details of what is going on--the vole story, as it were--is a fascinating
one. When prairie voles have sex, two hormones called oxytocin and vasopressin
are released. If the release of these hormones is blocked, prairie-voles' sex
becomes a fleeting affair, like that normally enjoyed by their rakish montane
cousins. Conversely, if prairie voles are given an injection of the hormones,
but prevented from having sex, they will still form a preference for their
chosen partner. In other words, researchers can make prairie voles fall in
love--or whatever the vole equivalent of this is--with an injection.
A clue to what is happening--and how these results might bear on the human
condition--was found when this magic juice was given to the montane vole: it
made no difference. It turns out that the faithful prairie vole has receptors
for oxytocin and vasopressin in brain regions associated with reward and
reinforcement, whereas the montane vole does not. The question is, do humans
(another species in the 3% of allegedly monogamous mammals) have brains similar
to prairie voles?
To answer that question you need to dig a little deeper. As Larry Young, a
researcher into social attachment at Emory University, in Atlanta, Georgia,
explains, the brain has a reward system designed to make voles (and people and
other animals) do what they ought to. Without it, they might forget to eat,
drink and have sex--with disastrous results. That animals continue to do these
things is because they make them feel good. And they feel good because of the
release of a chemical called dopamine into the brain. Sure enough, when a female
prairie vole mates, there is a 50% increase in the level of dopamine in the
reward centre of her brain.
Similarly, when a male rat has sex it feels good to him because of the
dopamine. He learns that sex is enjoyable, and seeks out more of it based on how
it happened the first time. But, in contrast to the prairie vole, at no time do
rats learn to associate sex with a particular female. Rats are not monogamous.
This is where the vasopressin and oxytocin come in. They are involved in
parts of the brain that help to pick out the salient features used to identify
individuals. If the gene for oxytocin is knocked out of a mouse before birth,
that mouse will become a social amnesiac and have no memory of the other mice it
meets. The same is true if the vasopressin gene is knocked out.
The salient feature in this case is odour. Rats, mice and voles recognise
each other by smell. Christie Fowler and her colleagues at Florida State
University have found that exposure to the opposite sex generates new nerve
cells in the brains of prairie voles--in particular in areas important to
olfactory memory. Could it be that prairie voles form an olfactory "image" of
their partners--the rodent equivalent of remembering a personality--and this
becomes linked with pleasure?
Dr Young and his colleagues suggest this idea in an article published last
month in the JOURNAL OF COMPARATIVE NEUROLOGY. They argue that prairie voles
become addicted to each other through a process of sexual imprinting mediated by
odour. Furthermore, they suggest that the reward mechanism involved in this
addiction has probably evolved in a similar way in other monogamous animals,
humans included, to regulate pair-bonding in them as well.
YOU MIGHT AS WELL FACE IT...
Sex stimulates the release of vasopressin and oxytocin in people, as well as
voles, though the role of these hormones in the human brain is not yet well
understood. But while it is unlikely that people have a mental, smell-based map
of their partners in the way that voles do, there are strong hints that the
hormone pair have something to reveal about the nature of human love: among
those of Man's fellow primates that have been studied, monogamous marmosets have
higher levels of vasopressin bound in the reward centres of their brains than do
non-monogamous rhesus macaques.
Other approaches are also shedding light on the question. In 2000, Andreas
Bartels and Semir Zeki of University College, London, located the areas of the
brain activated by romantic love. They took students who said they were madly in
love, put them into a brain scanner, and looked at their patterns of brain
The results were surprising. For a start, a relatively small area of the
human brain is active in love, compared with that involved in, say, ordinary
friendship. "It is fascinating to reflect", the pair conclude, "that the face
that launched a thousand ships should have done so through such a limited
expanse of cortex." The second surprise was that the brain areas active in love
are different from the areas activated in other emotional states, such as fear
and anger. Parts of the brain that are love-bitten include the one responsible
for gut feelings, and the ones which generate the euphoria induced by drugs such
as cocaine. So the brains of people deeply in love do not look like those of
people experiencing strong emotions, but instead like those of people snorting
coke. Love, in other words, uses the neural mechanisms that are activated during
the process of addiction. "We are literally addicted to love," Dr Young
observes. Like the prairie voles.
It seems possible, then, that animals which form strong social bonds do so
because of the location of their receptors for vasopressin and oxytocin.
Evolution acts on the distribution of these receptors to generate social or
non-social versions of a vole. The more receptors located in regions associated
with reward, the more rewarding social interactions become. Social groups, and
society itself, rely ultimately on these receptors. But for evolution to be able
to act, there must be individual variation between mice, and between men. And
this has interesting implications.
Last year, Steven Phelps, who works at Emory with Dr Young, found great
diversity in the distribution of vasopressin receptors between individual
prairie voles. He suggests that this variation contributes to individual
differences in social behaviour--in other words, some voles will be more
faithful than others. Meanwhile, Dr Young says that he and his colleagues have
found a lot of variation in the vasopressin-receptor gene in humans. "We may be
able to do things like look at their gene sequence, look at their promoter
sequence, to genotype people and correlate that with their fidelity," he muses.
It has already proved possible to tinker with this genetic inheritance, with
startling results. Scientists can increase the expression of the relevant
receptors in prairie voles, and thus strengthen the animals' ability to attach
to partners. And in 1999, Dr Young led a team that took the prairie-vole
receptor gene and inserted it into an ordinary (and therefore promiscuous)
mouse. The transgenic mouse thus created was much more sociable to its mate.
LOVE, LOVE ME DO
Scanning the brains of people in love is also helping to refine science's
grasp of love's various forms. Helen Fisher, a researcher at Rutgers University,
and the author of a new book on love*, suggests it comes in three flavours:
lust, romantic love and long-term attachment. There is some overlap but, in
essence, these are separate phenomena, with their own emotional and motivational
systems, and accompanying chemicals. These systems have evolved to enable,
respectively, mating, pair-bonding and parenting.
Lust, of course, involves a craving for sex. Jim Pfaus, a psychologist at
Concordia University, in Montreal, says the aftermath of lustful sex is similar
to the state induced by taking opiates. A heady mix of chemical changes occurs,
including increases in the levels of serotonin, oxytocin, vasopressin and
endogenous opioids (the body's natural equivalent of heroin). "This may serve
many functions, to relax the body, induce pleasure and satiety, and perhaps
induce bonding to the very features that one has just experienced all this
with", says Dr Pfaus.
Then there is attraction, or the state of being in love (what is sometimes
known as romantic or obsessive love). This is a refinement of mere lust that
allows people to home in on a particular mate. This state is characterised by
feelings of exhilaration, and intrusive, obsessive thoughts about the object of
one's affection. Some researchers suggest this mental state might share
neurochemical characteristics with the manic phase of manic depression. Dr
Fisher's work, however, suggests that the actual behavioural patterns of those
in love--such as attempting to evoke reciprocal responses in one's loved
one--resemble obsessive compulsive disorder (OCD).
That raises the question of whether it is possible to "treat" this romantic
state clinically, as can be done with OCD. The parents of any love-besotted
teenager might want to know the answer to that. Dr Fisher suggests it might,
indeed, be possible to inhibit feelings of romantic love, but only at its early
stages. OCD is characterised by low levels of a chemical called serotonin. Drugs
such as Prozac work by keeping serotonin hanging around in the brain for longer
than normal, so they might stave off romantic feelings. (This also means that
people taking anti-depressants may be jeopardising their ability to fall in
love.) But once romantic love begins in earnest, it is one of the strongest
drives on Earth. Dr Fisher says it seems to be more powerful than hunger. A
little serotonin would be unlikely to stifle it.
Wonderful though it is, romantic love is unstable--not a good basis for
child-rearing. But the final stage of love, long-term attachment, allows parents
to co-operate in raising children. This state, says Dr Fisher, is characterised
by feelings of calm, security, social comfort and emotional union.
Because they are independent, these three systems can work
simultaneously--with dangerous results. As Dr Fisher explains, "you can feel
deep attachment for a long-term spouse, while you feel romantic love for someone
else, while you feel the sex drive in situations unrelated to either partner."
This independence means it is possible to love more than one person at a time, a
situation that leads to jealousy, adultery and divorce--though also to the
possibilities of promiscuity and polygamy, with the likelihood of extra
children, and thus a bigger stake in the genetic future, that those behaviours
bring. As Dr Fisher observes, "We were not built to be happy but to reproduce."
The stages of love vary somewhat between the sexes. Lust, for example, is
aroused more easily in men by visual stimuli than is the case for women. This is
probably why visual pornography is more popular with men. And although both men
and women express romantic love with the same intensity, and are attracted to
partners who are dependable, kind, healthy, smart and educated, there are some
notable differences in their choices. Men are more attracted to youth and
beauty, while women are more attracted to money, education and position. When an
older, ugly man is seen walking down the road arm-in-arm with a young and
beautiful woman, most people assume the man is rich or powerful.
THESE FOOLISH THINGS
Of course, love is about more than just genes. Cultural and social factors,
and learning, play big roles. Who and how a person has loved in the past are
important determinants of his (or her) capacity to fall in love at any given
moment in the future. This is because animals--people included--learn from their
sexual and social experiences. Arousal comes naturally. But long-term success in
mating requires a change from being naive about this state to knowing the
precise factors that lead from arousal to the rewards of sex, love and
attachment. For some humans, this may involve flowers, chocolate and sweet
words. But these things are learnt.
If humans become conditioned by their experiences, this may be the reason why
some people tend to date the same "type" of partner over and over again.
Researchers think humans develop a "love map" as they grow up--a blueprint that
contains the many things that they have learnt are attractive. This inner
scorecard is something that people use to rate the suitability of mates. Yet the
idea that humans are actually born with a particular type of "soul mate" wired
into their desires is wrong. Research on the choices of partner made by
identical twins suggests that the development of love maps takes time, and has a
strong random component.
Work on rats is leading researchers such as Dr Pfaus to wonder whether the
template of features found attractive by an individual is formed during a
critical period of sexual-behaviour development. He says that even in animals
that are not supposed to pair-bond, such as rats, these features may get fixed
with the experience of sexual reward. Rats can be conditioned to prefer
particular types of partner--for example by pairing sexual reward with some kind
of cue, such as lemon-scented members of the opposite sex. This work may help
the understanding of unusual sexual preferences. Human fetishes, for example,
develop early, and are almost impossible to change. The fetishist connects
objects such as feet, shoes, stuffed toys and even balloons, that have a visual
association with childhood sexual experiences, to sexual gratification.
So love, in all its glory, is just, it seems, a chemical state with genetic
roots and environmental influences. But all this work leads to other questions.
If scientists can make a more sociable mouse, might it be possible to create a
more sociable human? And what about a more loving one? A few people even think
that "paradise-engineering", dedicated to abolishing the "biological substrates
of human suffering", is rather a good idea.
AS TIME GOES BY
Progress in predicting the outcome of relationships, and information about
the genetic roots of fidelity, might also make proposing marriage more like a
job application--with associated medical, genetic and psychological checks. If
it were reliable enough, would insurers cover you for divorce? And as brain
scanners become cheaper and more widely available, they might go from being
research tools to something that anyone could use to find out how well they were
loved. Will the future bring answers to questions such as: Does your partner
REALLY love you? Is your husband lusting after the au pair?
And then there are drugs. Despite Dr Fisher's reservations, might they also
help people to fall in love, or perhaps fix broken relationships? Probably not.
Dr Pfaus says that drugs may enhance portions of the "love experience" but fall
short of doing the whole job because of their specificity. And if a couple fall
out of love, drugs are unlikely to help either. Dr Fisher does not believe that
the brain could overlook distaste for someone--even if a couple in trouble could
inject themselves with huge amounts of dopamine.
However, she does think that administering serotonin can help someone get
over a bad love affair faster. She also suggests it is possible to trick the
brain into feeling romantic love in a long-term relationship by doing novel
things with your partner. Any arousing activity drives up the level of dopamine
and can therefore trigger feelings of romance as a side effect. This is why
holidays can rekindle passion. Romantics, of course, have always known that love
is a special sort of chemistry. Scientists are now beginning to show how true
* "Why We Love: The Nature and Chemistry of Romantic Love", by Helen
Fisher. Henry Holt and Company, New York.