1890 - 1962
Modern Evolutionary Synthesis
In the mid-1800s Gregor Mendel debunked the then current thinking of heredity as a process of blending the traits of the two parents (see Jean-Baptist Lamarck). Instead, heredity was driven by individual units (later called genes) that contained dominant and recessive variants. These units acted independently and recessive traits would be carried across generations and reemerge visibly (later called phenotype) when in the homozygous state. There was no blending of the dominant and recessive variations.
In 1859, Charles Darwin published his revolutionary concept of evolution by natural selection. This concept explained how environmental factors worked against the variations within species leading to the eventual emergence of new related species. Although Darwin overlapped with Mendel, he was unaware of Mendel's work and did not understand the mechanism of variation within species nor how that variation changed over time.
To many in the early twentieth century, there seemed to be an incompatibility between Mendelian inheritance and Darwinian evolution. How could the gradual evolution of species through natural selection be explained by genes that worked in step-wise, all-or-none gradations?
Sir Ronald A. Fisher, an Englishman, was a statistical genius who laid the foundations for modern experimental design. He was knighted in 1952. His contributions to biostatistics are foundational. He applied strict mathematical principles to Mendelian genetics to quantify and solidify the principles of natural selection and to explain how blended phenotypes can arise from what he called "particulate" inheritance. His work, along with J.B.S. Haldane and Sewall Wright is the basis for the field of population genetics. This work was later expanded by the geneticist Theodosius Dobzhansky into the modern evolutionary synthesis. This grand synthesis brought together key concepts of Darwinian evolution, Mendelian genetics, genetic drift and paleontology.
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