monogeny (n.)

word-forming element of Greek origin meaning "one, single, alone; containing one (atom, etc.)," from Greek monos "single, alone," from PIE root *men- (4) "small, isolated."

1864, in anthropology, "the doctrine that the human race is not one but consists of many distinct species" (opposed to monogeny or monogenism), from Late Greek polygenēs "of many kinds," from polys "many" (see poly-) + -genēs "born" (from PIE root *gene- "give birth, beget"). By c. 1970 the same word was used in a different sense, in reference to the theory that multiple genes contribute to the form or variant of some particular trait of an organism. Another word for the anthropological theory was polygenism (1857).