Complex sentence: Johann Friedrich Blumenbach and other monogenists such as Georges-Louis Leclerc, Comte de Buffon were believers in the "Degeneration theory" of racial origins the theory claims that races can degenerate into "primitive" forms.
Split into simpler sentences: Johann Friedrich Blumenbach and other monogenists such as Georges-Louis Leclerc, Comte de Buffon were believers in the "Degeneration theory" of racial origins. The theory claims that races can degenerate into "primitive" forms.