The man who says all he does facing profiteers

Man too does things which could seem to be against his own interest. Jean-Louis Dessalles from Telecom Paris, in an interesting conference called "human language, a paradox of evolution", shows that language should normally disadvantage its user: the one who shares information while the one who listens has simultaneously his own information and others'.

Yet we are descended from a man who talks. This fundamental invention that occured 100 or 200,000 years ago is even the reason of our intelligence according to Jacques Monod in "le hasard et la nécessité". What kind of Darwinian advantage Nature could give to one who speaks and gives information to others ?