During the last three hundred years, the average body mass of humans in developed countries has increased by over 50 percent, and our average longevity by over 100 percent. This extraordinary fact has nothing to do with natural selection of genes for bigger bodies; it has moved far too fast for that. It is a change—call it a technophysiolgiccal change—that has come about because we are better nourished. It also has not much to do with the variation in individuals' genetic potential. Some people will always be shorter than others: natural selection both allows for differences and selects for them. This story is about the rising average of population height.
It began around 1700, when agriculture was being brutally rationalized but also when trade between regions relieved some of the seasonal and yearly gluts and dearths of one's own homestead. It goes with the almost vertical rise in world population since then. The economist Robert Fogel argues that it reflects a whole suite of advantages. People with greater height, and appropriately larger body mass for height, live longer and suffer fewer illnesses in old age. Also they can work more: they do need more calories for basal metabolism, but, if fed, give proportionately higher physical output.
Most of the data concern men, because nations measure soldiers. This means there are sets of statistics to compare the veterans of the Union Army who lived until 1910 with veterans of World War II at the same age. There are also sets that track Europeans through the centuries. Adolescent males in Britain have grown taller each fifty years, just as the age of female menarche has been falling. Currently the tallest population in the world are the Dutch, who average 181 cm (just over 5'11"). In 1860, however, Dutch males averaged only 164 cm (under 5'5"). Other European countries had similar rises, as did the United States, to its present male average of 177 cm (under 5'10"). Fogel calculates that if the populations of Britain or France in the eighteenth and much of the nineteenth centuries had reached modem stature, they would have eaten up their whole countries' food supplies just for basal metabolism, with nothing left for work.
People who are children of immigrants to the United States frequently look down on the tops of their parents' heads. (Not all the growth is achieved in one generation: it takes several for the effects of previous maternal nutrition to wear off.) We laugh at the child-sized suits of armor for great medieval warriors. Modern men who live in quaint English Tudor houses develop a peculiar bobbing gait, to duck under every door lintel, and still they keep on cracking their heads. But seeing Fogel's figures makes us realize that something very peculiar is going on. For the first time since the strapping skeletons form Cro-Magnon days, we are living up to our genetic potential.