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dissipating advantage to those with longer appendages. Accordingly, people with rounded physiques (endomorphs) should have more difficulty with heat dissipation than will those with linear physiques (ectomorphs). Presumably, a given meal will produce greater thermic overload for the endomorph, who ought to learn, eventually, to eat less in the interests of thermoregulatory comfort.

There is substantial evidence that people adapt to a hot climate. Of course, eating less may be construed as an adaptation par excellence; but other related adaptations have been proposed. It is suggested above that heat can drive one's set-point for BW downward. Physical anthropologists (see Beller, 1977 for a fascinating review) have long noted a correspondence between physique and climate (Bergmann's rule, noted above). That linear physiques generally do better in the heat may be seen as an evolutionary selection principle, with races adapting to hot environments by altering their physique in an ectomorphic direction. One strong implication of this adaptational point of view is that certain people will do better in a hot environment than will others. Presumably, an individual who is genetically preadapted to a hot climate will have less trouble adapting to such a climate; such a displacement ought to disrupt his or her eating patterns less.

More pertinent to this discussion, perhaps, is the question of individual rather than evolutionary adaptation. Does, or can, an individual's set-point shift in response to heat exposure? If so, then the individual should feel uncomfortably overweight on initial exposure and cut back on eating; with a reduced set-point, the individual would eventually maintain a lower BW, and show a continued suppression of appetite appropriate for his or her more svelte physique.

Adaptation to Heat or Cold?

Interestingly, the endomorphy of a population is not correlated with mean annual temperature so much as with mean January temperature in northern latitudes (Beller, 1977). This finding has a number of implications, foremost among which is that normative BW depends more on extremes of cold than on heat. As an adaptation, this makes sense, because in these northern or temperate latitudes—and even in some tropical latitudes where the temperature occasionally plummets—the risk of insufficient fat/energy is greater than the risk of an excess of fat/energy. When one focuses on adaptation to hot climates, the implications are confusing. The main threat facing an individual in the hot climate would seem to be a failure of thermoregulation: heat dissipation is the main concern. Yet if the nighttime temperature drops precipitously, as may happen in the desert, then heat adaptation during the day may be more than cancelled out by cold adaptation at night. Conceivably, cold desert nights could lead to a continuing



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