Eugenics refers to a theoretical perspective developed in the late 19th century by a English mathematician named Sir Francis Galton. The theory posited that in order to create a human population without flaws, humanity could be preserved through selective breeding and the discouragement of reproduction from those humans perceived to have undesirable traits. Selective breeding and infanticide have both been terms associated with eugenics and motherhood. The term and the definition were heavily accepted by the upper and middle classes, primarily in the United States. Application of the theory was attempted in the early 20th century within the United States and later adopted by Adolf Hitler, demonstrated through eugenics experiments during World War II.