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Eugenics is the study of improving the human race by selective breeding. Its rationale is to remove bad or deleterious genes from the population, increasing the overall fitness of humanity as a result. Campaigns to stop the criminal, the poor, the handicapped, and the mentally ill from passing on their genes were supported in the past by such people as British feminist Marie Stopes and Irish playwright George Bernard Shaw. In the United States in the early 1900s, enforced sterilization was carried out on those deemed unfit to reproduce.

One problem with practical eugenics is who decides what is a desirable characteristic and what is not. Both before and during the World War II, there was a eugenics program in place in Nazi Germany. Initially this was carried out on inmates of mental institutions, but very quickly the reasons for sterilization became more and more arbitrary. After the World War II, there was a backlash against eugenics and anthropologists such as Franz Boas and Ruth Benedict championed the opposite view, tabula rasa (blank slate). This view favored the theory that humans are born with an empty mind, which is filled by experience. American anthropologist Margaret Mead carried out work in Samoa that confirmed these ideas, demonstrating that people are programmed by their environment, not by their genes, and that providing a decent environment produces people who behave decently towards each other. Modern work suggests that it is a subtle interaction of both the genetic make-up and the environmental conditions that shape an individual.

Eugenics happens to a minor degree in modern society, most notably when a couple with family histories of genetic disorders decide not to have children or to terminate a pregnancy, based on genetic screening. In 1994 China passed restrictions on marriages which involved individuals with certain disabilities and diseases.

There is evidence that the practice of eugenics could never be truly effective. When one calculates the frequency of deleterious alleles in the population, it is found humans all carry at least 1% of alleles which if present in homozygous form would prove fatal. When scientists predict the effects that might be achieved by preventing all individuals possessing a given allele from breeding, it is found that the effect would be minimal. One problem associated with this prediction is the difficulty in detecting certain alleles when they are present in the heterozygous form.

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Science EncyclopediaScience & Philosophy: Ephemeris to Evolution - Historical Background