It wasn't the kind of
passage you usually encounter in a strait-laced science journal: "I have
had to spend periods
of several weeks on a remote island in comparative isolation," Anonymous wrote in Nature. Curiously, he
continued, the day before he was due for shore leave his beard grew noticeably: "I have come to the conclusion
that the stimulus for (this) growth is related to the resumption of sexual activity."
Neither Anonymous nor his fellow scientists
were surprised that the aforementioned activity would loose a flood
of testosterone, which affects beards the way Miracle-Gro affects tomato plants. No, the weird part is that merely
anticipating female companionship did the trick.
Just as stress in the
med students I wrote about last week altered the expression of genes in
their immune systems,
so libidinous thoughts seem to affect gene expression, says developmental psychologist David Moore of Pitzer
College in Claremont, Calif. Thoughts can cause the release of hormones that can bind to DNA, "turning genes
`on' or `off.' "
If something as will-o'-the-wisp as a thought
can tweak genes, it's no surprise that more substantial influences can,
too. For instance, when R. Adron Harris and his team at the University of Texas, Austin, screened 10,000 genes
in the frontal and motor cortexes of alcoholics, they found changes in the expression of 191, they reported in last
month's Journal of Neurochemistry.
to cause "a selective reprogramming" of brain genes in areas involved in
judgment and decision
making, says Dr. Harris. Among them: genes that code for myelin, whose loss may impair cognition and judgment.
may also alter genes. The conventional wisdom is that drugs such as Prozac
work by blocking
re-uptake by brain neurons of the neurotransmitter serotonin. But Prozac starts doing that in 24 hours. Why, then,
do such drugs typically take weeks to lift depression? "The hunch is that Prozac works by altering gene
expression, maybe causing sprouting of new neurons and remodeling of synapses," Dr. Harris says.
too, can affect gene expression. How much a mother rat handles and licks
her offspring -- an
environmental influence if ever there was one -- has an astonishing effect: It determines whether genes that code
for receptors for stress hormones in the brain are expressed or not. And the level of those receptors affects how a
rat reacts to stress. Rats with attentive moms were much less fearful and more curious, finds Michael Meaney of
McGill University in Montreal. Rats that got less maternal handling grew up to be timid and withdrawn in novel
Rats are not long-tailed people, so you can't
infer that maternal affection affects gene expression and thus
temperament in babies, too. But something sure does. There is no shortage of evidence that intelligence, shyness,
impulsivity, risk-taking and illnesses have a genetic component.
But identical twins, who have the same genes,
don't have identical traits: One twin might be schizophrenic and the
other not, one might be shy and the other outgoing, one might get a "gene-based" cancer and the other not. The
difference between identical twins is the experiences they have and, if I may speculate, which of their genes are
What signal from the environment keeps schizophrenia-related
genes silent? What activates IQ-lifting genes?
Whatever it is, even a short-lived environmental signal might turn on genes that tell neurons how, and how much,
to grow. That would leave an enduring mark: Neural circuits would be complex or simple, and different brain
regions would be strongly linked or not. From such neuronal differences arise differences in intelligence and
personality, health and temperament.
Linking specific environmental
influences to gene activity would have been a pipe dream only a few years
the new technology of microarray analysis, in which "gene chips" reveal which DNA in a sample of tissue is
expressed and which is quiescent, is making such discoveries possible.
This past April, in one of their coolest uses so far, gene chips showed that the difference between human brains and chimp brains is not which genes each brain has. Those are nearly identical. The difference is which genes are turned on and which are switched off.
Ironically, the recognition
that genes depend on the environment follows hard on the heels of genetics'
triumph: sequencing the human genome. But what's now clear is that the more we learn about genetics, the more
we'll see that genes are not destiny.
©2002 Associated Press