The secular trend in human physical growth: a biological view.

Nutritionists and anthropometric historians alike are familiar with the secular trend-height and weight in adults, and the rate of physical development in children, increasing since at least the mid 19th century. The social conditions which drive this trend are of interest to anthropometric historians, but the underlying biology is also important. Here the trends for height, weight and menarcheal age are summarised and contrasted. In Northern Europe, adult height has largely stabilised, and the age of menarche has also settled at around 13 years, while weight continues to increase due to obesity. The increase in height from one generation to the next occurs mainly in the first 2 years of life, due to increases in leg length. The height trend has lasted for 150 years or more, i.e. for six generations, because the rate of catch-up from one generation to the next is biologically constrained to avoid the cost of too rapid catch-up.