Given that interaction and borrowing are possible reasons for the similiarities between languages, the original African language would have likely been influenced by the languages of the cultures it encountered and theoretically replaced. Merritt Ruhlen explains how that African language developed and why it is considered to be the original fully modern language .

There is, however, indirect circumstantial evidence from other areas of science that may provide an answer to these two questions. Both the archaeological record (in terms of bones and artifacts) and human genes (in terms of gene frequencies and mitochondrial DNA) indicate that all modern humans share a recent common ancestry in Africa. What is surprising, and difficult to explain, is that people who look just like us — modern humans — first appear in the archaeological record one hundred thousand years ago. But these people did not behave like us; they are indistinguishable from Neanderthals in both their toolkit and their behavior. It was only around fifty thousand years ago that — quite suddenly — both toolkits and behavior started to change with amazing rapidity. Toolkits that had remained unchanged over hundreds of thousands of years began to change with the rapidity of tennis-shoe styles today. And styles that had been uniform over huge geographical distances began to differentiate in neighboring villages. People began to fashion tools from other materials. Whereas previously only stone had been used, now bone, shells, ivory, and other natural materials were employed. Art appeared for the first time, burials became more complex, and people seem to have spread out of Africa to inhabit the entire world, replacing earlier inhabitants (Neanderthals) or occupying territories hitherto uninhabited, such as Australia, Oceania, and the Americas.

Merritt Ruhlen talks about the development of the fully modern language and possible reasons for a sudden change in language and human behavior.

Persisting in languages around the world are traces of the sudden expansion of humans at the time of the development of the original fully modern language. Merritt Ruhlen discusses how these traces can be seen in certain widespread roots as a result of their common origins.