2 19th Century Origins

Two geniuses of the last century provided the fundamental principles on which much of what we do today still depends. Francis Galton's boundless curiosity, ingenuity and passion for measurement were combined in seminal insights and contributions which established the foundations of the scientific study of individual differences. Karl Pearson's three-volume scientific biography of Galton is an enthralling testimony to Galton's fascination and skill in bringing a rich variety of intriguing problems under scientific scrutiny. His Inquiry into the Efficacy of Prayer reveals Galton to be a true ``child of the Enlightenment'' to whom nothing was sacred. To him we owe the first systematic studies of individual differences and family resemblance, the recognition that the difference between MZ and DZ twins provided a valuable point of departure for resolving the effects of genes and culture, the first mathematical model (albeit inadequate) for the similarity between relatives, and the development of the correlation coefficient as a measure of association between variables that did not depend on the units of measurement. The specificity that Galton's theory of inheritance lacked was supplied by the classical experiments of Gregor Mendel on plant hybridization. Mendel's demonstration that the inheritance of model traits in carefully bred material agreed with a simple theory of particulate inheritance still remains one of the stunning examples of how the alliance of quantitative thinking and painstaking experimentation can predict, in advance of any observations of chromosome behavior or molecular science, the necessary properties of the elementary processes underlying such complex phenomena as heredity and variation.