Smooth variables [in biology]

Despite their importance in understanding natural selection both in biology and in potential computational applications, the fundamental origins of smooth variables or so-called quantitative traits seem to have been investigated rather little. Within populations of organisms such traits are often found to have Gaussian distributions (as, for example, in heights of humans), but this gives little clue as to their origin. (Weights of humans nevertheless have closer to a lognormal distribution.) It is generally assumed that smooth variables must be associated with so-called polygenes that effectively include a large number of individual discrete genes. In pre-Mendelian genetics, observations on smooth variables are presumably what led to the theory that traits of offspring are determined by smoothly mixing the blood of their parents.