Going back to Pygmy and Bushmen origins?

At www.bbc.co.uk/science-environment-12665643 we learn that 'modern humans' may have originated in southern Africa according to a genetic study and a paper in PNAS. It seems that hunter gatherer populations such as the Bushmen possess a greater degree of genetic diversity than, shall we say, Bantu subsistence farmers, or cattle raising and herd based cultures. Why is this novel? – it was being said years ago (see Jean-Pierre Hallet, Pygmy Kitabu, Souvenir Press:1974). Professor Chris Stringer of the Natural History Museum was asked for his opinion of the new paper and managed to bring an air of composure to the BBC hack by saying Bushmen, Pygmies and the Sandawe of East Africa were much more widespread in the past – and inhabited most of Africa south of the Sahara. Hence, it may be true to say early humans have an origin in the hunter gatherers of southern Africa but that is only because they have been wiped out from other parts of Africa – and are in fact a small part of the population even in the southern part of the continent. Stringer also said that Bushmen and Pygmies probably contributed genes and behavioural characteristics to modern humans of all kinds but he did not think there was a single 'garden of eden' where modern humans evolved. We are diverse.