Dysgenics (also known as cacogenics ) is the study of factors producing the accumulation and perpetuation of defective or disadvantageous genes and traits in offspring of a particular population or species.

The adjective "dysgenic" is the antonym of "eugenic". It was first used c. 1915 by David Starr Jordan, describing the dysgenic effect of World War I. Jordan believed that healthy men were as likely to die in modern warfare as anyone else, and that war killed only the physically healthy men of the populace whilst preserving the disabled at home.