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Karl Pearson

Contributions to Biometrics
Karl Pearson was important in the founding of the school of biometrics, which was one of the competing theories to describe evolution and population inheritance at the turn of the 20th century. His series of eighteen papers, "Mathematical Contributions to the Theory of Evolution" established him at the founder of the biometrical school for inheritance. In fact, Pearson devoted much time during 1893 to 1904 to developing statistical techniques for biometry. These techniques, which are widely used today for statistical analysis, include the chi-squared test, standard deviation, and correlation and regression coefficients. Pearson's Law of Ancestral Heredity stated that germ plasm consisted of heritable elements inherited from the parents as well as from more distant ancestors, the proportion of which varied for different traits. Karl Pearson was a follower of Galton, and although the two differed in some respects, Pearson used a substantial amount of Francis Galton's statistical concepts in his formulation of the biometrical school for inheritance, such as the law of regression. The biometric school, unlike the Mendelians, focused not on providing a mechanism for inheritance, but rather on providing a mathematical description for inheritance that was not causal in nature. While Galton proposed a discontinuous theory of evolution, in which species would have to change via large jumps rather than small changes that built up over time, Pearson pointed out flaws in Galton's argument and actually used Galton's ideas to further a continuous theory of evolution, whereas the Mendelian's favored a discontinuous theory of evolution. While Galton focused primarily on the application of statistical methods to the study of heredity, Pearson and his colleague Weldon expanded statistical reasoning to the fields of inheritance, variation, correlation, and natural and sexual selection.

For Pearson, the theory of evolution was not intended to identify a biological mechanism to explain patterns of inheritance, whereas the Mendelian's postulated the gene as the mechanism for inheritance. Pearson criticized Bateson and other biologists for their failure to adopt biometrical techniques in their study of evolution. Pearson criticized biologists who did not focus on the statistical validity of their theories, saying "before we can accept [any cause of a progressive change] as a factor we must have not only shown its plausibility but if possible have demonstrated its quantitative ability" Biologists had succumb to "almost metaphysical speculation as to the causes of heredity," which had replaced the process of experimental data collection that actually might allow allow scientists to narrow down potential theories.

For Pearson, laws of nature were useful for making accurate predictions and for concisely describing trends in observed data. Causation was the experience "that a certain sequence has occured and recurred in the past". Thus, identifying a particular mechanism of genetics was not a worthy pursuit of biologists, who should instead focus on mathematical descriptions of empirical data. This, in part led to the fierce debate between the biometricians and the Mendelians, including Bateson. After Bateson rejected one of Pearson's manuscripts that described a new theory for the variability of an offspring, or homotyposis, Pearson and Weldon established Biometrika in 1902.