Scientific American February 1993 [antikvár]

LETTERS TO THE EDITORS Count on Confusion Robert M. May makes excellent points in "How Many Species Inhabit the Earth?" [Scientific American, October 1992]. I was especially taken by his suggestion that butterflies have attained the "honorary stams of birds." Giving the currently known species of butterflies as 17,500, he estimates the true number as no more than 20,000. Later in the same issue ("Singing Caterpillars, Ants and Symbiosis"), Philip J. De-Vries cites the number of known butterfly species as "more than 13,500." It presents a nearly perfect example of May's central thesis concerning the uncertainty of the number of taxa. Charles E. Diters U.S. Fish and Wildlife Service Sex Ratios at Work I am concerned that some of the opinions in "Sex Differences In the Brain," by Doreen Kimura [Scientific American, September 1992], are misleading and potentially damaging. Your readers deserve to know that Klmura's opinion regarding a biological foundation for occupational sex segregation is not shared by aU scientists. Whether the measured sex diiferences in certain cognitive and motor skills are "quite substantial" as she says is debatable. Certainly, none of them develops independent of social influences. Even if they did, the ratio of men and women in science and engineering would be closer to 50/50. In some fields of science and engineering, the current sex ratio is more than 90 percent men to fewer than 10 percent women. Kimura indicates that the sex differences range from approximately 0.20 standard deviation for one measure of verbal fluency to approximately 0.75 standard deviation for one of targeting skill. She calls the 0.75 effect size large. Yet the sex difference in adult height in the U.S. Is approximately 2.0 standard deviations. Thus, even the largest sex difference on any individual cognitive or motor test Is substantially smaller than the sex difference In height. The largest sex difference on any ability construct (defined by performance on several related tests) is that in vlsuospatial ability, which is only about 0.45 effect size units—a little less than one quarter the difference in height. Using an extreme assumption that wsuospatial ability is the only factor determining success as an engineer or physicist, one would expect about 60 percent of those jobs to be held by men and about 40 percent by women. Even if a person needed to score in the top 5 percent of the popuiation in vlsuospatial ability to succeed, a ratio of only about 70 men to 30 women would be predicted. Those predictions assume that the sex difference Is determined exclusively by factors that caimot be modifled by socialization or education, which is not true. Researchers studying sex segregation in occupations have concluded that the major determinants are economic and political, not hormonal. It would be difficult to explain the m^jor shifts in fields such as teaching and secretarial work, which men once dominated. In terms of biology. If women continue to be misinformed about their chances of succeeding as engineers and scientists, the sex ratios tn those professions are im-Ukely to change. As Beraadine Healy, the director of the National Instimtes of Health, stated In I99I, "It is safe to say that sustaining America's scientiflc preeminence wUl depend on attracting— and retaining—talented women." Per-pemation of stereotypes about sex and science works against this goal. Meussa Hines Department of Psychiatry and Biobehavloral Sciences School of Medicine, University of CaMfornia, Los Angeles Kimura replies: I agree that the reasons men and women are differentially represented across occupations are complex. Nevertheless, my claim that on the basis of biological predisposition, men and women would not be expected to be equally represented in all occupations is, I believe, a moderate view shared by most biological scientists in this field (most of whom are women). If one looks at a specific vlsuospatial ability such as mental rotaUon, the differences between men and women range across smdies from 0.70 to 1.0 in effect size. The sex differences in mathematical reasoning hover around 0.50. Even In the latter case, the ratio of men to women at the upper end of the distribution is very high, and it is differentiation at the upper end that is significant for certain professions. A recent smdy reported that girls with very high math achievement scores also tend to have interests and values that better suit them for nonscience fields. Such values are not necessarily determined by sociaUzation. The common inference that women are kept out of the sciences by systemic or deliberate discrimination is not based on evidence. One might as well argue that men are kept out of nursing careers by discrimination. Instead the process appears to be largely seff-selectlon. As for the deslrabiUty of attracting women to the physical sciences, that is a political, not a scientiflc. Issue. Still Scavenging Others have observed that modern parks appeal to us by recapitulating tiie East African savanna of our hominid ancestors. If Robert J. Blumenschlne and John A. Cavallo ["Scavenging and Human Evolution," Scientific American, October 1992] are right, another taste from that time may remain. The meat we buy in the supermarket, though called fresh, has generally been himg for a day or two to "age"—producing exactly the quality our vestigial scavenger instincts still prize: a delicate carrion tang. Stuart Gelzer Ardmore, Pa. Caveat Educator Three sample science questions, devised by an Individual who casts himself as a reformer of the science curricula in our schools, were posed in "Teaching Real Science," by Tim Beardsley [Scientific American, October 1992], It appears that we also need to be concerned about the English curricula, to wit Bill Aldridge's question: