Modern convention dictates that a single, consolidated period of sleep in each 24-hour period is ideal for human adults, but, in fact, early humans were likely polyphasic sleepers, meaning they experienced several sleep-wake cycles daily. Nowadays, the latter sleep pattern is generally reserved for extreme situations. Still, there are those who advocate its regular use as a means of increasing productivity. Which American futurist reportedly spent two years taking just four 30-minute naps a day? Discuss