'The immediate point was clear: America was a good place to live in the eighteenth century. Game was abundant, land free for the clearing, settlement sparse enough to prevent epidemics. On Komlos’s graph, even the runaway slaves are five feet eight, and white colonists are five feet nine—a full three inches taller than the average European of the time. “So this is the eighteenth century,” Komlos said, slapping the files. “This is not problematic. It shows that Americans are well nourished. Terrific.” He reached into a cardboard folder and pulled out another series of graphs. “What is problematic is what comes next.”
Around the time of the Civil War, Americans’ heights predictably decreased: Union soldiers dropped from sixty-eight to sixty-seven inches in the mid-eighteen-hundreds, and similar patterns held for West Point cadets, Amherst students, and free blacks in Maryland and Virginia. By the end of the nineteenth century, however, the country seemed set to regain its eminence. The economy was expanding at a dramatic rate, and public-hygiene campaigns were sweeping the cities clean at last: for the first time in American history, urbanites began to outgrow farmers.
Then something strange happened. While heights in Europe continued to climb, Komlos said, “the U.S. just went flat.” In the First World War, the average American soldier was still two inches taller than the average German. But sometime around 1955 the situation began to reverse. The Germans and other Europeans went on to grow an extra two centimetres a decade, and some Asian populations several times more, yet Americans haven’t grown taller in fifty years. By now, even the Japanese—once the shortest industrialized people on earth—have nearly caught up with us, and Northern Europeans are three inches taller and rising.
The average American man is only five feet nine and a half—less than an inch taller than the average soldier during the Revolutionary War. Women, meanwhile, seem to be getting smaller. According to the National Center for Health Statistics—which conducts periodic surveys of as many as thirty-five thousand Americans—women born in the late nineteen-fifties and early nineteen-sixties average just under five feet five. Those born a decade later are a third of an inch shorter.'
The massive immigration from Mexico and Latin America has an impact. 80% of all population growth is due to immigration.
Americans are a genetic melting pot. Immigrants are likely bringing the average down.
The obvious and simple reason is Americans have gone crazy about “low fat”, “low calorie”, “low red meat” diets. As that craze spread, so has diabetes, obesity and shorter Americans, not to mention low sperm counts.