Dale Carnegie observed decades ago in his bestseller, How to Win Friends and Influence People, that people prefer talking to listening. At first blush, this seems counterintuitive, as in most information exchanges, it's the receiver who gets the better bargain, by receiving information. So how did people evolve to prefer to give information than to receive it?

The answer, as is often the case, comes down to sex. In the tribal groups in which language evolved, the person doing the talking was more likely to get laid than his silent competitor. Thus, people with genes that caused them to talk more propagated in the population. 

Much like peacock's feathers, talking evolved as a way to show off to potential mates, and has been with us ever since.

Another benefit of the desire to talk is passing invaluable information to our progeny. Genes that make people want to teach their kids clearly made for better survival of the kids, and thus those genes expanded in the population.