How Humans Get Tall
Питание играло весьма посредственную роль. Я сделал перевод главного.
For most of human history, the world belonged to shorties. It wasn’t until well after the invention of cars and antibiotics that the average European man outgrew today’s average American teenaged girl.
Last year, Tim Hatton, an economist at the University of Essex in the U.K., rounded up data on the heights of European 21-year-olds dating from 1860 to about 1980. The results, published in the Oxford Economic Papers, were impressive: The average European man became about 11 centimeters taller between 1870 and 1970, gaining about a centimeter per decade.
On average, the Europeans grew faster than Latin Americans, South Asians, and Africans did. But the fact that the bulk of the height increase occurred in the early 20th century-through two world wars, poor healthcare, and a global economic recession-was puzzling. Food became cheaper between the wars, but people were also increasingly moving to cities and further from sources of fresh dairy and produce.
“It can't just be nutrition,” Hatton told me by phone. “There must be something else going on.”
When thinking about why we grow, it can help to visualize the body as a type of machine, as the economist Richard Steckel did:
“This machine expends fuel at rest (basal metabolism) amounting to some 1,200 to 1,400 calories per day (depending upon the size of the person) to breathe, keep warm, circulate the blood and so forth, and in physical effort, fighting infection and physical growth.”
We eat food to keep our inner engines running. Our bodies then use those calories to lengthen our bones and multiply our cells until we reach the end of puberty. But when we’re ravaged by infections or deprived of nutrients, growth takes a back seat to keeping the heart and organs functioning. If we’re struck by too many diseases and deficiencies, we stop short (literally) of the height we might have achieved. While about 80 percent of height is determined by genes, scientists now believe that nutrition and sanitation determine much of the rest.
Мы едим, чтобы поддерживать в рабочем состоянии наши внутренние двигатели. Наши тела затем используют эти калории, чтобы удлинять наши кости и умножать наши клетки, пока мы не достигнем конца полового созревания. Но когда мы заражены инфекцией или лишены должных питательных веществ, рост отходит на второй план, чтобы поддерживать на требуемомо уровне работоспособность сердца и прочих важных органов. Если мы поражены слишком многими заболеваниями и дефицитом питательных веществ, мы становимся ниже (в буквальном смысле) потециально возможного роста. В то время как около 80 процентов роста определяется генами, ученые теперь считают, что питание и гигиена во многом определяют остальное.
As the New Yorker’s Burkhard Bilger put it in 2004: “Height variations within a population are largely genetic, but height variations between populations are mostly environmental, anthropometric history suggests. If Joe is taller than Jack, it’s probably because his parents are taller. But if the average Norwegian is taller than the average Nigerian it’s because Norwegians live healthier lives.”
Your childhood environment can give you (or take away) three or four inches. A lack of nutrient-rich food and clean water explains why stunting is prevalentamong children in developing countries. Studies of North Koreans found that those born after the country was divided in two were about two inches shorter than their counterparts in the South.
When Barry Bogin, an anthropologist at Temple University, measured the heights of children from the Maya ethnic group, he found that Maya refugee children growing up in the United States were about four inches taller than Maya children who were still living in their native Guatemala. He chalked up the difference to America’s superior nutrition and healthcare.
As Hatton charted Europeans’ remarkable growth spurt, he also found that the increase in height corresponded with a simultaneous drop in infant mortality. But he wasn’t sure what was driving those two metrics.
For a new working paper, he wanted to examine what it was, exactly, about the life circumstances of those 20th-century Europeans that determined whether they became lanky or squat.
Hatton and his colleagues, Roy E. Bailey from the University of Essex and Kris Inwood from the University of Guelph, created a database of 2,236 British soldiers who served in World War I, and then they looked up their birth records. The soldiers were relatively representative of the male population as a whole-about two-thirds of the 1890 British male birth cohort enlisted. It turns out that subtle differences in their heights hinted at their origins:
- Those from white-collar backgrounds were taller: This follows the theory that wealth buys better food and living conditions, and thus greater height in adulthood. The men who hailed from the top two social classes stood a half-inch taller, on average.
- The more kids there were in a household, the shorter they were: Not only because there was less food to go around, but also because it made it more likely that there were more people in each bedroom. “Crowding can help spread respiratory and gastrointestinal infections,” Hatton said. “People sneezing on each other, that sort of thing.” Each additional sibling cost the men an eighth of an inch, and having more than one person per bedroom shaved off a quarter-inch.
- Children of literate mothers were taller: When mothers couldn’t read, they were less likely to know about the importance of a balanced diet or clean cutlery. The researchers measured the percentage of women by region who were only able to sign their marriage certificates with an X, rather than their name. People from areas with a high percentage of illiterate mothers were a quarter-inch shorter.
- People from industrial districts were shorter than those from agricultural areas: Regardless of income, the Dickensian living conditions of 19th century British cities suppressed height by about nine-tenths of an inch. On top of being hit with factory pollution, urban dwellers were packed into filthy, disease-ridden slums. Jacob's Island, a poor area of London, in 1840 (Wikimedia Commons) As Kellow Chesney described in The Victorian Underworld, “Hideous slums, some of them acres wide, some no more than crannies of obscure misery, make up a substantial part of the metropolis … In big, once handsome houses, thirty or more people of all ages may inhabit a single room.”
“Together these developments help to explain the apparent puzzle of rapid improvement in average health status during a period of war and depression that predates the advent of universal health services,” Hatton and his colleagues wrote.
For centuries, Americans were the NBA players of the world. We were two inches taller than the Red Coats we squared off against in the American Revolution. In 1850, Americans had about two and a half inches on people from every European country. But our stature plateaued after World War II, and since then, other countries shot past us. White Americans have grown a bit taller since the early 1980s, but African Americans haven’t.
Now, the Dutch are the tallest, at an average of six feet for men and five-foot-seven for women. They’ve come a long way: In 1848, a quarter of Dutch men were rejected from military service because they didn’t meet the five-foot-two height limit. “Today, fewer than one in 1,000 is that short,” the Associated Press noted in 2006. (The tallest people on record, though, are apparently the people of the Dinaric Alps, in the former Yugoslavia, where adolescent males are, on average, six-foot-one monoliths.)
The Danes, Norwegians, and Germans stack up right under the Dutch. American men and women, meanwhile, measure just 5’9" and 5’4", respectively, barely edging out the Southern Europeans.
John Komlos, an economic historian who has studied height extensively, thinks we Americans lost our height advantage because of poorer overall healthcare and nutrition compared to Europe. Our social shortcomings, he believes, are literally making us come up short.
"American children might consume more meals prepared outside of the home, more fast food rich in fat, high in energy density and low in essential micronutrients," he and co-author Benjamin E. Lauderdale of Princeton University wrote in 2006. "Furthermore, the European welfare states provide a more comprehensive social safety net including universal health care coverage."
That’s probably not the full story - immigration and fertility changes play a role too, after all. Our slipping height advantage might, in the end, be far less meaningful than measures like life expectancy or obesity. And of course, there's nothing wrong with being petite.
But given that how tall we grow reflects how well we grew up, the trend of the incredible shrinking American is worth paying attention to. (с) источник
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