Book excerpt: Carlson's history of degeneracy theory, the idea that certain people are biologically disposed to become socially unfit or "degenerate," examines the birth of both good and bad eugenics movements. While good eugenics movements focus on people whose needs may require intense social attention and expensive social investments, bad eugenics movements call for isolation if not eradication and genocide. He brings the history into the present day, where the potential misapplication of DNA science and social attitudes toward the human genome could lead to similar movements.