Comments on life, the universe and everything from an aging Sixties survivor.

Location: Massachusetts, United States

Ummm, isn't "about me" part of the point of the blog?

Friday, June 25, 2010


Fredric:"You Must be Igor."
Igor:"No. It's pronounced Eye-gor."
Fredric:"They told me Igor."
Igor:"They were wrong then,weren't they?"

(Young Frankenstein)

Back we go to Mr. Chanda and his assertions regarding body surface area and its effect on cooling.

Mr. C stands exonerated on one point, the main one, but culpable on a second point, lack of clarity. He mentioned that this point refers to the ratio of body surface area to body volume (SA:V) but didn't stay around the point long enough to explain how the ratio works.

The zoological premise in play here is Allen's Rule , which maintains among other things that endotherms (including humans) of the same volume may have differing surface areas, which will aid or impede their temperature regulation. (There's actually a better explanation in Wikipedia, but I generally avoid linking there.)

In general:
  • Low surface area to volume ratio tends to conserve heat
  • High surface area to volume ratio tends to dissipate heat
Chanda's rain forest dweller has a high SA:V ratio by virtue of having a small body, which incidentally generates less heat to start with. African plains dwellers also have a high SA:V ratio through having a very elongated body. This is an illustration of evolutionary biology's irritating habit of having more than one solution for the same problem. Chanda mentions the proportionately small heads and shoulders, but skips the more important fact, the length of the limbs in proportion to the trunk. Since there is proportionately less variation in trunk length than limb length amongst adult humans, the best way for the organism to increase surface area and remain physically active is to have longer limbs. There is, of course, the Jabba the Hutt model, but that suffers from lack of mobility. It's also debatable whether Jabba was an endotherm.

There are other selection factors at work, so one can't go to the wall with Allen's Rule. Those other factors are one reason we can have different heat dissipation solutions. For example, a very tall plains hunter or herder has several advantages over a short one: being able to see farther is just one. A very short rainforest dweller has advantages in that environment over a tall person: being able to move more quietly and hide more easily are among them.

A better illustration than Chanda's, and one consistent with Allen's Rule, is between the African plains dwellers such as the Fur, the Dinka, and the Masai, and the Inuit of Arctic North America. The Africans have a very high surface area to volume ratio achieved in part with very long limbs. The Inuit have a low surface area to volume ratio achieved in part by having relatively short limbs. The Inuit also have relatively heavy layers of fatty tissue, which increases body volume.

In discussing the rain forest people, Chanda veers toward the more controversial Bergmann's Rule, which maintains that within the same species, larger individuals appear in higher latitudes and smaller ones in equatorial latitudes. The latter have a high surface area to volume ratio more or less because they are small, and thus are better adapted to a tropical climate. Bergmann's hypothesis is subject to many exceptions, elephants being the most obvious. Neither rule is considered absolute these days, because both open the field to so many alternate explanations.

So Chanda's statement is correct. The two populations have reached two different solutions to the same problem--heat dissipation.

Back to business. The weakness of tall=well nourished as an absolute principle has always been that it is one-dimensional and contains a very heavy dose of projection. The argument exists in part to support a mythical faith in human progress. For example, we are assured that people have uniformly grown taller since the Middle Ages, as a marker of progress. The Dutch evidence sharply contradicts this. My own studies with British military records, done some 35 years ago, likewise contradict the conventional wishful thinking. Contemporary observations from the 15th century onward contradict a faith in progress that begins to seem naive. Nutrition is a factor in human growth, but just one factor in a matrix of environmental, statistical, genetic and epidemiological factors. You have to look at all of them together to come close to the picture.


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