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Health

Patterns of human height & lifestyle

Gene ExpressionBy Razib KhanDecember 27, 2010 2:02 AM

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Steve Hsu, The mystery of height:

I was looking at The Formosan Encounter: Notes on Formosa's Aboriginal Society, A Selection of Documents from Dutch Archival Sources. The Dutch came to Taiwan (then called Formosa) in the early 17th century and these translated documents record their impressions of the Austronesian natives. (Both the Dutch and Chinese settlers traded with the natives during this period.) One report states that the aboriginal men were taller by a head and neck, on average, than the Dutch. (The average Dutchman came only to the shoulder of the average native?) Another report describes the aborigines as tall and sturdily built, like semi-giants. This paper on historical Dutch height suggests that 17th century Dutchmen were about 170 cm or so on average. Holland was the richest country in Europe at the time, but nutritional conditions for average people were still not good by modern standards. So how tall were the aborigines? Presumably well above 180cm since "a head and neck" would be at least 20cm! (Some Native Americans were also very tall when the Europeans first encountered them.) But, strangely, the descendants of these aborigines are not known for being particularly tall. This paper reports that modern day aboriginal children in Taiwan are shorter than their Han counterparts. On the other hand, the Dutch are now the tallest people in the world, with average male height exceeding 6 feet (183 cm). This kind of reversal makes one wonder whether, indeed, most groups of humans have similar potential for height under ideal conditions, as claimed here. (Note the epigenetic effects -- several generations of good nutrition might be required for a group to reach its full height.)

And now from the The Economist:

About 12,000 years ago people embarked on an experiment called agriculture and some say that they, and their planet, have never recovered. Farming brought a population explosion, protein and vitamin deficiency, new diseases and deforestation. Human height actually shrank by nearly six inches after the first adoption of crops in the Near East....

Here is one model which I am in some sympathy with:

Constant warfare was necessary to keep population density down to one person per square mile. Farmers can live at 100 times that density. Hunter-gatherers may have been so lithe and healthy because the weak were dead. The invention of agriculture and the advent of settled society merely swapped high mortality for high morbidity, allowing people some relief from chronic warfare so they could at least grind out an existence, rather than being ground out of existence altogether.

The indigenous people of the Andaman Islanders in the Bay of Bengal are often classed as "Negritos." This is in part a reference to their small size. But here is a description of the only population which has refused outside contact, the Sentinelese:

From the boat one could not made out their facial features but they appeared to be of a fairly good height. As our landing parties approached the beach the Sentinelese disappeared into the forest....

Here's a video of a later contact with the Sentinelese. They seem to be a trim and normally proportioned people, though I can't judge their heights too well. In developed nations height is about ~80-90% heritable. That means that most of the population variance in height can be attributed to variance in genes. The distribution of heights of children are well predicted by the heights of parents. But what about between population differences? A great deal of this is obviously due to different environmental inputs. And yet some differences do seem to remain on the margin. Then there is the strange fact that American whites are now shorter than population-controlled Europeans, an inversion of the 19th century pattern. A combination of epigenetics, genetic variation, and the balance of nutritional inputs, explain much of the world wide variation. Ten years ago I probably would have weighted #2 more than I do now. I suspect that the balance of nutrients, and not just the amount of calories, matters more than we might have thought. This may explain much, though not all, of the decrease in height with the shift from hunter-gatherer lifestyle to farming. Farming can extract an order of magnitude more calories per unit of land, but at the cost of nutritional diversity. Also, in regards to short hunter-gatherer populations such as the Bushmen, Pygmies, and many of the Negritos, their social and cultural marginalization has a lot of complex downstream effects (though please note black Americans have about the same mean height as white Americans, so we need to be careful here). Australian Aborigines are not particularly short, suggesting that long term co-existence with agriculturalists may have had an impact on other hunter-gatherer groups, as they were pushed into marginal lands, and exposed to the density dependent diseases of farmers. It is the last element which I believe explains some of the size difference of the Sentinelese from other Andaman Islanders. It may be that the common microbial flora of Eurasians has a deleterious impact on isolated populations, and results in low grade morbidity which shifts the development of these groups. When a group of Andamanese were separated from Indians in the 1960s they recovered much of their health, and the population began to grow again.

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