I believe language evolved because it facilitated trade. If you wanted X, being able to say “X?” made it a thousand times easier to find someone with excess X. This efficiency required prior language learning, of course. Language learning happened in the background, so to speak, then paid off in the foreground by making one of human life’s biggest tasks (trading) much easier.
After reading this excellent article about netbooks, I realized they’re like language. All sorts of tasks become much easier for your computer if the heavy lifting is done by a server. You no longer need Word or Photoshop, for example. Just as using language to trade required prior language learning, using netbooks this way requires prior software development.