Linguists are tracing the origins and evolutions of languages. The evidence they use is independent of genetics, but the methodology is quite similar. As with the human genome, they are certain that human language originated in Africa, where they find the greatest diversity of phonemes.
A widespread language family in Africa is Bantu. Its origins can be traced to the highlands between Cameroon and Nigeria, right near Bioko.
But before that time, all humans had apparently evolved ‘universal grammar’ and an innate facility for language. The evolution of this facility must have required selection pressures in which sophisticated language was important. This facility was selected for in babies and children, just as physical features such as furless bodies and subcutaneous fat (blubber) were selected for. In the process of natural selection, babies and children with better language abilities were more likely to have many offspring when they became adults.
If humans were scattered around Africa as small groups of 'Hunter-gatherers', there would have been no selection pressures to evolve universal grammar. However, if thousands of humans were living for millions of years along the shores of Bioko as ‘Free-sharing floaters’, with their main activities being singing and talking, a facility for language would have been an important factor in their reproductive success.
As groups of humans left the island, mainly between 200,000 and 50,000 years ago, they invented vocabularies for new activities and situations. Each group developed its own language. They had already evolved the facility for universal grammar.
Maps from: https://en.wikipedia.org/wiki/Bantu_expansion