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The Case of the Deformed Frogs

Norman Johnson

A Plague of Frogs: The Horrifying True Story. William Souder. xv + 299 pp. Hyperion, 2000. $23.95.

Hormonal Chaos: The Scientific and Social Origins of the Environmental Endocrine Hypothesis. Sheldon Krimsky. xiii + 284 pp. The Johns Hopkins University Press, 2000. $35.95.

Off on a nature studies field trip in rural Minnesota, junior high school students discover several frogs with abnormal or missing legs. After initial skepticism, various scientists confirm the students' findings, observing many more classes of abnormalities—extra limbs, deformed jaws, shriveled testes and others—present at high frequencies in several frog species in numerous locales across the state. The scientists begin to worry whether what is happening to the frogs might signal possible dangers to humans.

The above is not the teaser to the latest thriller or X-Files episode; this story is all the more horrifying because it is true. A Plague of Frogs does, however, read like a mystery novel—one with several detectives in pursuit of the culprit, sometimes working at cross-purposes. Tensions between field-oriented naturalists and lab-oriented "gene jockeys" and between university researchers and those employed by governmental agencies (such as the Environmental Protection Agency) make for interesting subplots.

In addition to providing a good science detective story, Souder demonstrates how science—in particular, evolutionary and environmental biology—is done. "Real science," Souder explains, "is about inference and interpretation, about formulating hypotheses that can withstand every test to which they are put. To make anything from your data you need a skeptical soul." He deftly introduces relevant concepts in developmental and evolutionary biology, often employing striking imagery and analogies, and expresses himself vividly—maintaining, for instance, that "a frog with a deformed leg or with the wrong number of legs is ? not merely abnormal, it's an insult to 350 million years of evolution."

A mink frog (<em>Rana septentrionalis</em>)Click to Enlarge Image

Almost immediately after the discovery of the deformities, attention focused on two major hypotheses for their cause: parasites and chemicals. (Curiously, both have intellectual underpinnings from Susan Bryant's developmental biology lab at the University of California, Irvine.) Evaluation of the hypotheses requires an understanding of how frogs develop. Previous studies showed that parasites, when encapsulated within tiny tadpoles, could disrupt limb bud development. Upon encountering foreign matter (the parasite), the limb bud cells would alter their patterns of division, which would eventually result in the formation of extra limbs. The question is whether parasites can and do cause the spectrum of deformities seen at the Minnesota sites.

Methoprene is the leading suspected chemical. Used to control mosquitoes, it acts like an insect juvenile hormone and thus prevents the mosquitoes from maturing. According to the chemical hypothesis, methoprene or a similar chemical may disrupt the development of limb buds in frogs by behaving like a vertebrate hormone.

The chemical hypothesis for the frog deformities is a subset of the broader environmental endocrine hypothesis (EEH), which is the subject of Hormonal Chaos. The premise behind the EEH is that chemicals mimicking endocrine hormones can bind to receptors and thus can cause health problems in humans as well as other animals. Krimsky shows how this hypothesis first developed within the scientific community, in large part as a result of the persistence and insight of Theo Colborn. While working for the nonprofit Conservation Foundation in the 1980s, Colborn formulated the EEH, linking together evidence from several disparate sources: deleterious effects on wildlife exposed to pesticides, defects in babies whose mothers took the estrogen substitute diethylstilbestrol (DES) and controversial claims that human sperm is declining in quantity and quality.

After tracing the development of the EEH within the scientific community, Krimsky then discusses debates of the EEH within the arena of policy-making and describes how elements of the EEH came to the attention of politicians spanning the political spectrum from then-Senator Alphonse D'Amato to his colleague John Glenn. The press began covering the EEH during the early 1990s, and in 1996 the publication of Our Stolen Future, written by Colborn with Dianne Dumanoski and Pete Myers, led to a dramatic increase in the number of media reports and commentaries on the EEH. In the particularly illuminating section of Hormonal Chaos devoted to the reviews and coverage of Our Stolen Future and the EEH in general, Krimsky demonstrates the biases of different media outlets.

How should we make policy in cases when the science is suggestive but not conclusive and the stakes are high? "From a policy standpoint," Krimsky states, "it may be considered rational to act as if the hypothesis were true while retaining one's scientific skepticism." As a precedent, he notes that asbestos use was strictly restricted even amid continuing debate about the extent to which it caused cancer.

A Plague of Frogs and Hormonal Chaos differ with respect to their intended audiences, with the former being better suited for a general audience. Hormonal Chaos, though, is an excellent guide for those interested in the details of the interplay between science and environmental public policy. Hormonal Chaos (and to a lesser extent A Plague of Frogs) also discusses gradations in strength of evidence and in strength of the relationships between variables and thus should appeal to those interested in the philosophy of science.

In fiction, and especially in television shows, mysteries are wrapped up quickly, often with the capture of the bad guy. Real life is not as simple, and the case of the deformed frogs is still not "solved." Parasites are part of the cause but not the whole cause of the deformities. Souder concludes that "The question as to what threat these other causes pose to humans remains as problematic today as it did ? in 1995."

Despite our ignorance about the causes, we do know that the current level of deformities across many frog species is unusually high. We also know that population sizes of numerous amphibian species have been declining over the past two decades. Although the extent to which these facts bode ill for human health is still debatable, the frogs themselves are in peril.

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