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Chemistry Between People Is More Than Just a Saying

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TIMES MEDICAL WRITER

After decades of speculation, false leads and heated controversy, University of Chicago scientists finally appear to have proved the existence of human pheromones--odorless chemicals released by one person that affect the behavior of another.

Psychologists Martha K. McClintock and Kathleen Stern report today in the journal Nature that they have identified two pheromones collected from the underarms of women--one that lengthens the menstrual cycle and one that shortens it.

The compounds may eventually find use in helping infertile women conceive, but the confirmation of pheromones’ existence may have much greater ramifications for the individual human psyche and human social behavior.

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Researchers suspect that other pheromones may control sexual activity, human compatibility, group behavior and other social activity, just as they do in animals.

Now that two pheromones have been found, some speculate that it will become easier to identify others.

The report “clearly shows, for the first time, that the potential for chemical communication involving sexual function has been preserved in humans during evolution,” according to psychologist Aron Weller of Bar-Ilan University in Israel.

McClintock and Stern’s paper “is going to be a classic,” added Charles Wysocki of the Monell Chemical Senses Center in Philadelphia. “Now we need to find out how [the pheromones] work.”

The term “pheromone” was coined 39 years ago by researchers studying insects. They found that insects secreted odorless chemicals that could alter the behavior of other insects of the same species. Pheromones have subsequently been shown to induce a variety of behaviors in virtually all insects and animals.

The chemicals determine, for example, with which partners hamsters mate, how dominance relationships develop among male elephants and when rat mothers wean their pups. Female monkeys in heat release a pheromone that serves as an aphrodisiac to males.

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But it has never been clear whether humans secrete and respond to pheromones in the same manner as other animals.

The first evidence that they might was collected by McClintock when she was an undergraduate at Wellesley College in the late 1960s. In a now-famous paper published in Nature in 1971, she documented that the menstrual cycles of women living closely together in dormitories or other social groups became synchronized.

“This was one of the first real examples of social interactions affecting basic biology,” McClintock said.

Other researchers have confirmed her finding and observed the same effect in lesbian couples.

In the current study, McClintock and Stern identified 29 women, ages 20 to 35, with a history of regular ovulation. Nine of the women wore cotton pads placed over the axillary glands under their armpits for eight-hour periods in the early portion of their menstrual cycle and, later, during ovulation. The pads were then cut into quarters, moistened with alcohol and frozen.

They were collected in this fashion because animal studies had shown that different pheromones are secreted at different times of the cycle.

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Then, each day for two months, the pads were wiped under the noses of the other 20 women in the study. The pads collected early in the menstrual cycle were found to shorten the menstrual cycle in 68% of the women exposed to them.

In contrast, the pads collected later, during ovulation, lengthened the menstrual cycle in 68% of the women exposed to them. Cycles were shortened by one to 14 days and were lengthened by one to 12 days.

McClintock had previously developed computer simulations showing that this kind of lengthening and shortening of the cycle produces the menstrual synchronization she observed in her earlier studies. She had also demonstrated an identical effect in rats and isolated the rat pheromones that produce it.

The new study, she said, “demonstrates that humans have the potential to communicate pheromonally.”

Unlike earlier, heavily criticized studies that have attempted to demonstrate the presence of pheromones, McClintock’s “is a very well-done piece of work,” Wysocki said. “I doubt that there will be any serious criticism because of the elegance of design and execution.”

George Preti of Monell, who led one of those earlier studies, was pleased to see McClintock’s findings. “This bears us out, shows that we were right,” he said.

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Researchers must now find out what the pheromones are and how they work, a process that may take years because they are present in such small amounts.

In most other animals, but not all, pheromones are detected by a special organ in the nose called the vomeronasal organ or VNO.

Until a few years ago, most scientists believed that humans did not possess a VNO. Although researchers have now shown that it is present in humans, many experts, perhaps a majority, still think that it is vestigial tissue with no function. (Plastic surgeons remove the VNO during cosmetic surgery on the nose.)

But McClintock noted that there are other ways pheromones could work their magic. For example, there might be other receptors in the nose, or pheromones might simply be absorbed through tissues, like cocaine is absorbed, she noted.

Once the pheromones are identified, most agree, they could be used to regulate fertility. For example, the compounds could be used with women who are infertile because of irregular menstrual cycles. On the other hand, they could also be manipulated to provide birth control by making women less fertile.

Despite the new proof of the existence of human pheromones, experts cautioned, there is still no evidence that hormones influence other types of sexual behavior. Perfumes and fragrances purporting to contain human pheromones, Wysocki said, “have never been shown to produce reliable and valid responses” in members of the opposite sex.

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(BEGIN TEXT OF INFOBOX / INFOGRAPHIC)

The Pheromones Phenomenon

Many scientists think pheromones--odorless chemicals released by one person to affect the behavior of another--are detected in humans by the vomeronasal organ in the back of the nose, which may transmit signals to the hypothalmus. Others, however, think that other tissues are sensitive to the hormones.

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