“It is argued in this study that language, as we know it today, probably began to emerge about 20,000 years ago.”

In an impressive feat of mental gymnastics the linguist then claims that it likely spread from Africa (because all good things must come from Africa). If he was not so blinded by ideology, he could look for evidence of diffusion in the real world. There is plenty. Dogs were domesticated more than 15,000 years ago in Eurasia, and spread the whole world over. Or, of course, bullroarer mystery cults, seven sisters of the pleiades, snake myths, etc.

More likely, the linguist has a belief that full language evolved and spread late, and then has to find a way to make this palatable to his colleagues.