thumb|right|200px|Ronald Fisher in 1912The Correlation between Relatives on the Supposition of Mendelian Inheritance is a scientific paper by British statistician and geneticist Ronald Fisher which was published in the Transactions of the Royal Society of Edinburgh in 1918, marking a significant milestone in genetics. In this study, Fisher integrated Mendel's principles of inheritance with statistical techniques to clarify how characteristics could manifest as both continuous (such as height or weight) and still be regulated by distinct genetic factors.

Background

thumb|right|200px|[[Karl Pearson]]

Mendelian inheritance was rediscovered in 1900. However, there were differences of opinion as to the variation that natural selection acted upon. The biometric school, led by Karl Pearson followed Charles Darwin's idea that small differences were important for evolution. The Mendelian school, led by William Bateson, however thought that Gregor Mendel's work gave an evolutionary mechanism with large differences. Joan Box, Fisher's biographer and daughter states in her 1978 book, The Life of a Scientist that Fisher, then a student, had resolved this problem in 1911.

Although Gregor Mendel demonstrated that plant traits were inherited in specific combinations, the first researcher to demonstrate that people inherit many physical attributes continuously was Francis Galton. Galton (1875) used statistical techniques he developed  particularly correlation, regression, and variance to study similarities between relatives and to understand how much population differences were due to chance. He also used his statistical knowledge in genetics, and described heritability as something that can be measured using probability and distributions.

Later, Karl Pearson extended Galton's use of statistics in biology by developing the field of "biometry," which is the statistical examination of biological diversity. However, it would take another generation before Fisher (1918), synthesizing the earlier work of Mendel, Galton and Pearson, found a way to reconcile the earlier research into an overall theory of heredity. Fisher showed that if multiple genes were involved in the determination of a single trait, then continuous variation could result from the action of Mendelian genetics. Pearson's models could accurately describe variation but not its genetic basis. His view of heredity was one of blending parental influences rather than discrete, particulate inheritance.

Later scholarship has shown that the divide between the Mendelian and biometric traditions was not as rigid as once thought. Researchers such as Pearson were already exploring ways to connect statistical and genetic ideas. Early genetics represented a spectrum of approaches rather than a strict opposition between two schools of thought. This intellectual diversity, ranging from Galton's descriptive statistics to Pearson's mathematical formalism, provided the groundwork for Ronald A. Fisher, who would later unite Mendelian genetics with biometry. Fisher's synthesis formed the theoretical basis of population genetics and the study of quantitative traits. Fisher's analysis resolved the long-standing dispute between biometricians and Mendelians by demonstrating that continuous variation could emerge naturally from Mendelian inheritance if a trait were influenced by many genes of small effect.

In this work, Fisher introduced the statistical concept of variance as a way to quantify variability within a population. He showed that total phenotypic variance could be separated into two main components: genetic variance, resulting from inherited factors, and environmental variance, resulting from non-genetic influences. This idea became central to the emerging field of quantitative genetics. By defining variance and its additive properties, Fisher laid the foundation for modern approaches to estimating heritability and predicting how traits respond to natural or artificial selection.

References

  • The University of Adelaide has made the original available in pdf format: [http://digital.library.adelaide.edu.au/dspace/bitstream/2440/15097/1/9.pdf]