[Paleopsych] NYT: A Gene for Romance? So It Seems (Ask the Vole)
checker at panix.com
Tue Jul 19 19:30:52 UTC 2005
A Gene for Romance? So It Seems (Ask the Vole)
By NICHOLAS WADE
Biologists have been making considerable progress in identifying
members of a special class of genes - those that shape an animal's
behavior toward others of its species. These social behavior genes
promise to yield deep insights into how brains are constructed for
certain complex tasks.
Some 30 such genes have come to light so far, mostly in laboratory
animals like roundworms, flies, mice and voles. Researchers often
expect results from these creatures to apply fairly directly to people
when the genes cause diseases like cancer. They are much more hesitant
to extrapolate in the case of behavioral genes. Still, understanding
the genetic basis of social behavior in animals is expected to cast
some light on human behavior.
Last month researchers reported on the role of such genes in the
sexual behavior of both voles and fruit flies. One gene was long known
to promote faithful pair bonding and good parental behavior in the
male prairie vole. Researchers discovered how the gene is naturally
modulated in a population of voles so as to produce a spectrum of
behaviors from monogamy to polygamy, each of which may be advantageous
in different ecological circumstances.
The second gene, much studied by fruit fly biologists, is known to be
involved in the male's elaborate suite of courtship behaviors. New
research has established that a special feature of the gene, one that
works differently in males and females, is all that is needed to
induce the male's complex behavior.
Social behavior genes present a particular puzzle since they involve
neural circuits in the brain, often set off by some environmental cue
to which the animal responds. Catherine Dulac of Harvard has found
that the male mouse depends on pheromones, or air-borne hormones, to
decide how to behave toward other mice. It detects the pheromones with
the vomeronasal organ, an extra scent-detecting tissue in the nose.
The male mouse's rule for dealing with strangers is simple - if it's
male, attack it; if female, mate with it. But male mice that are
genetically engineered to block the scent-detecting vomeronasal cells
try to mate rather than attack invading males.
The mice have other means - sound and sight - of recognizing male and
female. But curiously, nature has placed the sex discrimination
required for mating behavior under a separate neural circuit aroused
through the vomeronasal organ.
"It was very surprising for us," Dr. Dulac said.
The gene that was eliminated from the mice is a low-level member of a
presumably complex network that governs the inputs and outputs
necessary for mating behavior. The most striking behavioral gene
discovered so far is a very high level gene in the Drosophila fruit
The gene is called fruitless because when it is disrupted in males
they lose interest in females and instead form mating chains with
other males. The male's usual courtship behavior is pretty fancy for a
little fly. He approaches the female, taps her with his forelegs,
sings a song by vibrating his wing, licks her and curls his abdomen
for mating. If she is impressed she slows down and accepts his
proposal. If not, she buzzes her wings at him, a gesture that needs no
All these behaviors, researchers discovered several years ago, are
controlled by the fruitless gene - fru for short - which is switched
on in a specific set of neurons in the fly's brain. The gene is
arranged in a series of blocks. Different combinations of blocks are
chosen to make different protein products. The selection of blocks is
controlled by a promoter, a region of DNA that lies near but outside
the fru gene itself.
So far four of these fru gene promoters have been found. Three work
the same way in both male and female flies. But a fourth selects
different blocks to be transcribed, making different proteins in males
and in females. This difference, it seemed, was somehow the key to the
whole suite of male courtship behaviors.
Last month Barry J. Dickson of the Austrian Academy of Sciences
provided an elegant proof of this idea by genetically engineering male
flies to make the female version of the fruitless protein, and female
flies to generate the male version. The male flies barely courted at
all. But the female flies with the male form of fruitless aggressively
pursued other females, performing all steps of male courtship except
How does the male form of the fruitless protein govern such a complex
behavior? Dr. Dickson and his colleagues have found that the protein
is produced in 21 clusters of neurons in the fly's brain. The neurons,
probably connected in a circuit, presumably direct each step of
courtship in a coordinated sequence.
Surprisingly, female flies possess the same neuronal circuit. The
presence of the male form of fruitless somehow activates the circuit ,
in ways that are still unknown.
Fruitless serves as a master switch of behavior, just as other known
genes serve as master switches for building an eye or other organs.
Are behaviors and organs constructed in much the same way, each with a
master switch gene that controls a network of lower level genes?
Dr. Dickson writes that other such behavior switch genes may well
exist but could have evaded detection because disrupting them - the
geneticist's usual way of making genes reveal themselves - is lethal
for the fly. (Complete loss of the fruitless gene is also lethal, and
the gene was discovered through a lucky chance.)
Though researchers like to focus on specific genes, they are learning
that in behavior, an organism's genome is closely linked to its
environment, and that there can be elaborate feedback between the two.
Honeybees spend their first two to three weeks of adult life as nurses
and then switch to jobs outside the hive as foragers for the remaining
three weeks. If all foragers are removed from a hive, the nurse bees
will sense the foragers' absence through a pheromone and assume their
own foraging roles earlier. As the colony ages however, there are too
few nurses, so some bees stay as nurses far longer than usual.
Gene Robinson, a bee biologist at the University of Illinois, has
found that a characteristic set of genes is switched on in the brains
of nursing bees and another set in foraging bees. This is an effect of
the bees' occupation, not of their age, since both the premature
foragers and the elderly nurses have brain gene expression patterns
matched to their jobs.
Evidently the division of labor among bees in a hive is socially
regulated through mechanisms that somehow activate different sets of
genes in the bees' brains.
A remarkable instance of genome-environment interaction has been
discovered in the maternal behavior of rats. Pups that receive lots of
licking and grooming from their mothers during the first week of life
are less fearful in adulthood and more phlegmatic in response to
stress than are pups that get less personal care.
Last year, Michael J. Meaney and colleagues at McGill University in
Montreal reported that a gene in the brain of the well-groomed pups is
chemically modified during the grooming period and remains so
throughout life. The modification makes the gene produce more of a
product that damps down the brain's stress response.
The system would allow the laid-back rats to transmit their behavior
to their pups through the same good-grooming procedure, just as the
stressed-out rat mothers transmit their fearfulness to their
"Among mammals," Dr. Meaney and colleagues wrote in a report of their
findings last year, "natural selection may have shaped offspring to
respond to subtle variations in parental behavior as a forecast of the
environmental conditions they will ultimately face once they become
independent of the parent."
A full understanding of these behavior genes would include being able
to trace every cellular change, whether in a hormone or pheromone or
signaling molecule, that led to activation of the gene and then all
the effects that followed. Dr. Robinson has proposed the name
"sociogenomics" for the idea of understanding social life in terms of
the genes and signaling molecules that mediate them.
The genes discovered so far mostly seem to act in different ways and
it is hard to state any general rules about how behavior is governed.
"It's early days and we don't have enough information to develop
theories," Dr. Robinson said.
A question of some interest is how far the genetic shaping of behavior
exists in people. Larry J. Young of Emory University, who studies the
social behavior of voles, said that, in people, activities like the
suckling of babies, maternal behavior and sexual drives are likely to
be shaped by genes, but that sexual drives are also modulated by
"The genes provide us the background of our general drives, and
variations in these genes may explain various personality traits in
humans, but ultimately our behavior is very much influenced by
environmental factors," he said.
Researchers can rigorously explore how behavioral genes operate in
lower animals by performing tests that are impossible or unethical in
people. "The problem with humans is that it is extremely difficult to
prove anything," Dr. Dulac said. "Humans are just not a very good
More information about the paleopsych