In 1885, Francis Galton, a British biologist, published a paper in which he demonstrated with graphs and tables that the children of very tall parents were, on average, shorter than their parents, while the children of very short parents tended to exceed their parents in height (cited in Walker 1929). Galton referred to this as "reversion" or the "law of regression" (i.e., regression to the average height of the species). Galton also saw in his graphs and tables a feature that he named the "co-relation" between variables. The stature of kinsmen are "co-related" variables, Galton stated, meaning, for example, that when the father was taller than average, his son was likely also to be taller than average. Although Galton devised a way of summarizing in a single figure the degree of "co-relation" between two variables, it was Galton's associate Karl Pearson who developed...