This from Scientific American:
February 12th [wa]s the 200th birthday of Charles Darwin and Abraham Lincoln. But they’re linked by something else, too.
Before Darwin, natural philosophers held to a point of view called typology, or essentialism. Members of a particular class were all the same. For example, all triangles have the same fundamental characteristic: three sides.
This way of thinking, however, extended to the biological world, including humans.
As the great evolutionary biologist Ernst Mayr wrote in an essay in the July, 2000, issue of Scientific American, “For the typologist, Caucasians, Africans, Asians or Inuits are types that conspicuously differ from other human ethnic groups. This mode of thinking leads to racism.”
But Darwin replaced typology with the new concept of populations.
Groupings of organisms are populations of unique individuals—who vary. Typology offered a philosophical justification for a slave being worth three fifths of a white person in the Constitution. But now science insisted that all people, regardless of race, were fully human. A viewpoint that finally began to be put in practice in the U.S. by Lincoln.