Some branches deteriorated more than others. The other idea was that Biblical creation produced only the white race. Other races were produced by separate and lesser creations. That falls apart as we learn more about genetics. Races are far less well-defined than we'd thought.
Racial identity is a pitifully small part of genetic makeup.
Those genealogical arguments have died only in recent times. Hitler, and even Henry Ford, were still using them a scant sixty years ago. Meanwhile, the geographic question has lasted just as long. Since the Biblical accounts were written by tribes of the Eastern Mediterranean, that's where 19th-century scholars thought the human species arose. When the first australopithecine skull turned up in South Africa, in 1924, scientists, who'd been looking for human origins in Asia, rejected the find.