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Saturday, December 25, 2010

The mystery of height

Academia Sinica (where I am on sabbatical) has a small bookstore that my kids always drag me to. Ordinarily I am happy to spend embarrassingly large amounts of time at a bookstore, but this place has only a small collection of English books. Over time, I think I've flipped through most of them! Yesterday 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.)

In the nineteenth century, when Americans were the tallest people in the world, the country took in floods of immigrants. And those Europeans, too, were small compared with native-born Americans. Malnourishment in a mother can cause a child not to grow as tall as it would otherwise. But after three generations or so the immigrants catch up. Around the world, well-fed children differ in height by less than half an inch.* In a few, rare cases, an entire people may share the same growth disorder. African Pygmies, for instance, produce too few growth hormones and the proteins that bind them to tissues, so they can’t break five feet even on the best of diets. By and large, though, any population can grow as tall as any other.

* I'm not sure where this statement comes from, since, for example, Japanese still seem to be a few inches shorter than, say Europeans. But it's also true that even the modern Japanese diet is lower in protein and calcium than the corresponding European or American one.

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