Is the 20th century increase in human height entirely nongenetic?

The twentieth-century increase in human height in affluent nations may not be entirely due only to such nurturant considerations as food supply and electric lights. A possible genetic role might be found in interactions of food supply, maternal pelvic size, and height-survival/vulnerability links, and in mate selection. Humans seem to be following the paleontological principle that most species tend to evolve larger sizes over time.