Study
Finds Signs of Elusive Pheromones in Humans
By NATALIE ANGIER
hey
may be odorless and colorless and their function may be mysterious,
but human pheromones at last have the zest of scientific truth.
Researchers at the University of
Chicago have demonstrated that compounds swabbed from the underarms of
young women at different times of the month can alter the length of
other women's menstrual cycles, compressing or expanding the cycles in
predictable fashion.
The experiments offer the first solid
proof of the existence of human pheromones, compounds produced by one
individual that can influence the biology or behavior of another. Over
the last few decades, scientists have identified a wide variety of
insect and animal pheromones, but until now, the evidence for their
relevance to human affairs has been circumstantial, equivocal and
bitterly contested.
The new results, being reported
Thursday in the journal Nature, show that people are indeed capable of
being led by the nose.
"This is a very exciting study
that is going to make a lot of researchers sit up and take
notice," said Dr. Charles Wysocki of the Monell Chemical Senses
Center in Philadelphia. "It has the experimental safeguards and
controls that have been lacking in the past."
The findings also cast new light on the
widely discussed but much disputed phenomenon of menstrual synchrony,
in which women who live together supposedly find their monthly cycles
coinciding over time. Dr. Martha McClintock, the senior researcher in
the new study, first reported her observations of menstrual synchrony
in 1971. Since then, some researchers have confirmed her finding,
while others have failed to find supporting evidence for it.
The latest data reveal that women
release a complex bouquet of pheromones throughout the month, with the
result that synchronicity among female roommates is possible, but by
no means guaranteed.
"Finding menstrual synchrony was
like finding a fossil tooth," said Dr. McClintock. "Thirty
years later, we've excavated the whole beast, and it turns out to be a
whole lot more interesting than that first tooth alone."
She and her co-author, Kathleen Stern,
have determined that compounds taken from the underarm secretions of
women who were in the early, or follicular, phase of the menstrual
cycle can shorten the cycle of women exposed to the extracts.
By contrast, compounds extracted from
the women at midcycle, when they are ovulating, can have the opposite
effect on recipients, lengthening their menstrual cycle. Underarm
effluvium taken from women after ovulation, in the luteal phase of the
cycle, has no detectable impact on the timing of other women's
periods.
The researchers have yet to isolate the
actual pheromones, but they said the work might eventually yield new
birth-control methods and treatments for infertility.
Other researchers predicted that the
discovery would throw wide the door on pheromone research. They said
that subliminal chemical cues very likely underlay many human
behaviors, including mate choice, nepotism, dominance struggles, even
xenophobia.
"Now we can stop horsing around
and go after these chemicals to find out what they are," said Dr.
Thomas Eisner, a chemical ecologist at Cornell University in Ithaca,
N.Y. "There should be no barrier to the isolation and elucidation
of these molecules."
Scientists emphasized that humans were
unlikely to be as rigidly beholden to pheromones as are certain other
creatures. When an ovulating female boar is exposed to a pheromone
from a male boar's saliva, for example, she immediately freezes into a
spread-legged mating posture, a fact that pig farmers use to
facilitate artificial insemination.
In the new study, the scientists asked
nine healthy women to wear cotton pads under their arms for eight
hours at a stretch during distinct phases of their cycles. The pads
were then cut into sections, treated with alcohol, and wiped under the
noses of 20 other women every day for a month. The recipients said
they could smell nothing from the pads except the alcohol used as a
suspension.
The effects of the applications,
however, were quick and significant. In 68 percent of the women, the
follicular-phase extracts shortened their current menstrual cycle by
anywhere from one to 14 days, with an average abridgment of 1.7 days.
When the same group of women were later swabbed with ovarian-phase
extracts, a different 68 percent of them were affected, this time by a
lengthening of their cycle by from one to 12 days, with an average
expansion of 1.4 days.
Because the pheromonal compound either
stretched or condensed a recipient's cycle depending on its origin,
the new study circumvents complaints about previous studies, when
critics pointed out that the random fluxes of women's periods could
make coincidental convergence look like pheromonally orchestrated
synchrony.
What remains unknown is why women are
sensitive to one another's menstrual cycles in the first place. The
McClintock laboratory has shown that communal ovulation occurs in
rats, and that the female rats benefit by being able to conceive, give
birth to and nurse their pups en masse. Through a sharing of
lactational duties, the females rear larger offspring more quickly
than they do when nursing on their own.
Thus it makes sense for rats to have a
method of communicating their reproductive status to their peers, and
for dilatory cyclers to speed up or fast cyclers to slow down in order
to coordinate their timing of ovulation and conception. In theory,
ancestral women might also have benefited from group cycling, group
mothering, and the ability to breast-feed one another's young.
But Dr. Jane Lancaster, an
anthropologist at the University of New Mexico in Albuquerque, said
human gestation and lactation were too drawn out for the rodent form
of communalism to apply.
"Great apes don't have that kind
of group synchronicity, so why should we?" Dr. Lancaster said.
Instead, Dr. Lancaster hypothesized
that a young woman who is entering puberty might benefit from being
responsive to the cycles of her mother and older sisters.
"In this case, competent ovulators
help their female kin during development to become regular cyclers and
ovulators themselves," she said. Alternatively, women might use
pheromones aggressively, as part of female-female competition.
Co-wives of a polygamous man might seek to suppress one another's
fertility, for example.
"Reproduction is a very
time-consuming, risky business," Dr. McClintock said. "The
more cues a female has to her social setting, and whether this is the
right time to try getting pregnant, the better off she'll be."
In other words, nosiness pays.
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Pheromones Story
