Mendelian Inheritance, Intelligence Testing, And American Eugenics
Galton's eugenic ideas found fertile ground in America after 1900, when scientists rediscovered Mendel's findings regarding the inheritance of physical traits in pea plants. Mendel's notions of "dominant" and "recessive" genetic traits, easily identified in "lower" organisms such as plants and animals, convinced people that human eugenic improvement was possible. Scientists assumed that even complex human traits such as intelligence and behavior behaved as simple genetic "unit characters," such as height or color in peas.
The advent of intelligence testing in the 1900s provided a new way to quantify Galton's notion of genius. American eugenicists assessed an individual's eugenic worth by combining his intelligence quotient (IQ) with a Galtonian study of the family pedigree. Psychologist Henry Herbert Goddard published one famous study, The Kallikak Family, in 1912. Goddard traced two family lines that originated with a common male ancestor, whom he called Martin Kallikak (from the Greek words for beautiful [kalos] and bad [kakos]). One branch appeared healthy and eugenic, descended from Martin's marriage to a "respectable" woman. The second branch was composed of "Defective degenerates" (alcoholics, criminals, prostitutes, and particularly the mentally "feebleminded") born of Martin's dalliances with a "feebleminded" tavern mistress. Goddard thus "proved" the inheritance of feeblemindedness, and its social cost.
Convinced that "feeblemindedness" and other complex antisocial behaviors behaved like simple Mendelian traits, eugenicists lobbied for compulsory sterilization laws. Between 1907 and the mid-1930s, such laws were adopted by thirty-two American states. The U.S. Supreme Court upheld these laws in 1927, when Justice Oliver Wendell Holmes ruled that, "the principle that sustains compulsory vaccination of schoolchildren is broad enough to cover the cutting of the fallopian tubes. … Three generations of imbeciles are enough." "Feebleminded" individuals were prominent among the more than 60,000 individuals sterilized in the United States under eugenic sterilization laws between 1927 and 1979.