Copyright © 1998 by McGraw-Hill, Inc. All rights reserved. Printed in the United States of America. The entire contents or parts of this Update may be reproduced for use with Physical Anthropology, Sixth Edition, or Physical Anthropology: The Core, second edition, by Philip L. Stein and Bruce M. Rowe, provided each reproduction bears the copyright notice. The publisher's written pd èbssion must be obtained for other use.
See Physical Anthropology, 6th edition, Chapter 12, page 285; Physical Anthropology: The Core, 2nd edition, Chapter 8, page 197.
In the animal kingdom, behavior is often regulated by chemicals called pheromones. These can be defined as "airborne chemical signals that are released by an individual into the environment and which affect the physiology or behaviousXêj other members of the same species." These compounds are not detected by an individual as an odor, but they do produce a clear change in the behavior of the individual.
Many scientists believe that humans, whose behavior is thought to be primarily the result of learning, do not produce or respond to pheromones in any significant way. However, it has been known for some time that women living together will often synchronize their menstrual cycles. This fact suggested to many biologists thauXõeeromones exist in humans.
Recently Kathleen Stern and Martha K. McClintock have reported the results of experiments that suggest that human pheromones do exist. Experiments have shown that rats also synchronize their menstrual cycles, and two rat pheromones have been identified that serve to lengthen and shorten the menstrual cycle. The same phenomenon has been found to work in humans.
The researchers took samples of secretions from the armpit of women and exposed the secretionrXña other women. These axillary compounds taken from women before ovulation (the late follicular stage) shortened the menstrual cycles of recipient women by 1.7 ± 0.9 days. On the other hand, axillary compounds taken from women at the time of ovulation had the opposite effect. They lengthened the menstrual cycle of recipients by 1.7 ± 0.9 days. Thus the shortening and lengthening effects of the two compounds would, over time, serve to synchronize the menstrual cycles of women living together.
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Reference: K. Stern and M. K. McClintock, "Regulation of Ovulation by Human Pheromones," Nature, 392 (12 March 1998), 177-179.