Magazine article American Scientist

Letters

Magazine article American Scientist

Letters

Article excerpt

Seeing Is Believing

To the Editors:

Henry Petroski's Engineering column "The Evolution of Eyeglasses" (September-October) is characteristically informative. Petroski suggests that we do not know why centuries passed between the invention of eyeglasses and the invention of telescopes and microscopes. Vasco Ronchi provided a clear and persuasive explanation in his 1970 book The Nature of Light. He noted 13th-century scholars' "emphatic and unanimous" rejection of the idea that glass lenses could have any consequences for science. Ronchi explains that glass lenses were qualitatively incompatible with ancient Greek theories of optics, which, strange as it may seem, were still predominant in the late Middle Ages. It took almost three centuries for the visible facts of lenses to overcome this entrenched theoretical bias. A closely related discussion is provided in a paper I recently published in Ecological Psychology.

A particularly vivid depiction of the early use of (and fears about) eyeglasses can be found in The Name of the Rose, Umberto Eco's novel of early 14th-century monastic murder and intrigue. Eco's protagonist, William of Baskerville, owns a pair of spectacles, knows when they were invented, and confesses that he often refrains from wearing them in public, fearing that they (and, by implication, he) might be thought diabolical.

Thomas Stoffregen University of Minnesota Minneapolis, MN

Only Human

To the Editors:

I especially enjoyed Pat Shipman's column "Why Is Human Childbirth So Painful?" (Marginalia, NovemberDecember). As a former professor of gross anatomy, I have always subscribed to the "obstetrical dilemma hypothesis." But after reading this column, I tend toward the alternative that childbirth has become more difficult as improved diet has increased newborn body size. Humans have enjoyed a calorie-rich diet from well before the dawn of what is called civilization. So one might have to go back to the early hominid Australopithecus to compare precivilization human brain, pelvis, and body sizes.

From 1976 to 1994 my primary National Institutes of Health grant was to investigate relationships between protein-calorie nutritional insufficiency and brain growth and development. My previous work has made me wary of broad conclusions based on measurements of humans' growth, because the variation that one can observe among individuals is so huge. In the matter of body and brain size for age, we have no idea what is biologically "normal" for Homo sapiens. Pediatricians can show mothers growth charts, which are founded on a limited sample, but they can't say what is normal. Somewhere at the intersections of physiology, anatomy, genetics, and physical anthropology, there are probably answers. I would love to see the brain sizes of Australopithecus, Homo erectus, Homo neanderthalensis, and other hominids plotted for comparison with Holly Dunsworth's plots of brain size in modem humans and apes.

Regardless of the mother's nutritional circumstances, I am aware that it is exceedingly difficult to undernourish a fetus in utero, but I do think an anthropological approach to the obstetricalenergetics debate would yield valuable information. Diet may be a key factor.

Richard Wiggins Apex, NC

To the Editors:

I enjoyed reading Pat Shipman's column concerning "Why Is Human Birth So Painful?" but was troubled by the anthropocentric approach and some

factual errors. Dr. Shipman is wrong when she states, "Human newborns are unique among mammals [that give birth to a single young] in that our babies cannot immediately get up, feed, and walk around." The order Chiroptera (bats) contains over 1,000 species, and about 90 percent give birth to only a single offspring at a time, as detailed in a paper that Thomas Kunz and I published in the Symposia of the Zoological Society of London in 1987. Although developmental state at birth varies among species, many bats are bom blind, hairless, and helpless. …

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