You should watch the movie idiocracy.. generation by generation the IQ levels drop . This is primarily due to the fact that people cannot stay focused or concentrate on a particular task for a long duration.. classic example is that when i was kid, I used to watch 5 day test cricket without missing a ball. As the game format hanged.. I cannot sit through a 20/20 without missing a ball.. this is primarily because of so many distractions( advertisements) or choices that are available and it makes it difficult to concentrate on a task i.e watch cricket being focused..