Describe at least one manifestation of 20th century public policy that was based in Darwinian thought ... or ...

One example of public policy that was based on Darwinian thought is that of eugenics. Eugenics is the idea of trying to improve the genetic quality of a population by not allowing the reproduction of certain groups, and encouraging the reproduction of others. Although the concept of eugenics predates Darwin, it gained scientific support after his theory of evolution.

The concept is heavily disputed. Moreover, it carries negative associations due to its identification with the policies of Nazi Germany. However, eugenics was influential in a variety of regimes during the 20th century. In America, this was embodied in the American Eugenics Society, founded in 1922.