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Greulich, “A comparison of the physical growth and development of American-born and native Japanese children,” p. 304.
         Greulich didn’t realize this at the time, but it was a perfect illustration of how genes really work : not dictating any predetermined forms or figures, but interacting vigorously with the outside world to produce an improvised, unique result.
       Two excellent summaries from two of the top figures in the field of gene-environment interaction:
    A key feature of gene expression is that it can be altered in a reversible way by extra-cellular signals and by environmental influences. Although DNA starts off the causal chain, what really matters is the expression of the genes (in terms of messenger RNA). There are no genetic effects without this expression. (Rutter, Moffitt, and Caspi, “Gene-environment interplay and psychopathology,” p. 229.)

    Individual genes and their environments interact to initiate a complex developmental process that determines adult personality. Most characteristic of this process is its interactivity: Subsequent environments to which the organism is exposed depend on earlier states, and each new environment changes the developmental trajectory, which affects future expression of genes, and so forth. Everything is interactive, in the sense that no arrows proceed uninterrupted from cause to effect; any individual gene or environmental event produces an effect only by interacting with other genes and environments. (Turkheimer, “Three laws of behavior genetics and what they mean,” p. 161.)
         in truth human height has fluctuated dramatically over time .
    This from height anthropologist Richard Steckel: “We have 1200 years of adult male height trends in Northern Europe that show that height was greatest in the early middle ages, when there was a warmer climate, and reached a minimum in the Little Ice Age of the 17th and 18th centuries.” (Steckel, “Height, Health, and Living Standards Conference Summary,” p. 13.)
    Also: American and British teenagers were six inches taller, on average, than their predecessors a century earlier. (Ceci, Rosenblum, DeBruyn, and Lee, “A Bio-Ecological Model of Intellectual Development.”)
         The New Yorker ’s Burkhard Bilger : Bilger, “The Height Gap.”
    A few more excerpts from Bilger’s piece:
    Though climate still shapes musk oxen and giraffes—and a willowy Inuit is hard to find—its effect on industrialized people has almost disappeared.Swedes ought to be short and stocky, yet they’ve had good clothing and shelter for so long that they’re some of the tallest people in the world. Mexicans ought to be tall and slender. Yet they’re so often stunted by poor diet and diseases that we assume they were born to be small.
      Biologists say that we achieve our stature in three spurts: the first in infancy, the second between the ages of six and eight, the last in adolescence. Any decent diet can send us sprouting at these ages, but take away any one of forty-five or fifty essential nutrients and the body stops growing. (“Iodine deficiency alone can knock off ten centimetres and fifteen I.Q. points,” one nutritionist told me.)
      Steckel, after his work on slaves, went on to Union soldiers and Native Americans. (The men of the northern Cheyenne, he found, were the tallest people in the world in the late nineteenth century: well nourished on bison and berries, and wandering clear of disease on the high plains, they averaged nearly five feet ten.) Then he enlisted anthropologists to gather bone measurements dating back ten thousand years. In both Europe and the Americas, he discovered, humans grew shorter as their cities grew larger. The more people clustered together, the more pest-ridden and poorly fed they became. Heights also fell in synch with global temperatures, which reached a nadir during the Little Ice Age of the seventeenth century.
      Around the time of the Civil War, Americans’