In 1868 in England, Charles Darwin proposed his pangenesis theory to describe the units of inheritance between parents and offspring and the processes by which those units control development in offspring. Darwin coined the concept of gemmules, which he said referred to hypothesized minute particles of inheritance thrown off by all cells of the body. The theory suggested that an organism's environment could modify the gemmules in any parts of the body, and that these modified gemmules would congregate in the reproductive organs of parents to be passed on to their offspring. Darwin's theory of pangenesis gradually lost popularity in the 1890s when biologists increasingly abandoned the theory of inheritance of acquired characteristics (IAC), on which the pangenesis theory partially relied. Around the turn of the twentieth century, biologists replaced the theory of pangenesis with germ plasm theory and then with chromosomal theories of inheritance, and they replaced the concept of gemmules with that of genes.

Theodosius Dobzhansky studied genetics and evolutionary biology, primarily using fruit flies, in the Soviet Union and the United States during the twentieth century. Scholars credit his widely read 1937 book Genetics and the Origin of Species with providing one of the earliest and most impactful integrations of Charles Darwin’s theory of evolution by natural selection with Gregor Mendel’s theory of genetics and therefore contributing significantly to the Modern Synthesis. In his research, Dobzhansky studied wild populations of organisms such as fruit flies and found that populations of the same species can differ in the frequency of one or more genetic traits. Understanding the role of such genetic diversity in evolution became a central theme of his research. Later in his career, he wrote about the social implications of his research, including the relationship between biological and cultural notions of race. Through both his scientific papers and popular writings, Dobzhansky shaped the course of evolutionary biology in the twentieth century and influenced public discussions of race in the years following World War II.