Our ancestors slept a lot more than we do. Back in the ice age, the daily cycle of being asleep or awake depended on the natural daily cycle of night and day. Our pineal gland near the base of our brain had evolved over millions of years to control when we sleep and when we wake based on the presence or absence of natural light. However, thanks to Thomas Edison and his invention and perfection of the light bulb, our pineal gland can be easily confused. While artificial light allows us the freedom to safely do anything at any time of day, it also interrupts our natural sleep patterns. With natural winter periods of day and night, our ancestors may have slept up to 16 hours! But thanks to artificial light our daylight has been lengthened and our sleep has been shortened to less than half that amount.
We have, however, managed to remain healthy and function very well if given 8 full hours of sleep. The problem is that very few people actually sleep for eight hours. Forty million Americans suffer from sleep disorders. 43% of our population is moderately to severely sleep deprived. We watch TV and surf the web too late. We consider sleep a luxury when it is really a necessity. Ideally, you should get about 10 hours of sleep, but eight will suffice.
Evidence of the first three side effects (obstructed memory, concentration and reaction time) is clear when you consider that 3 of the worst catastrophic mistakes in history were made when the people in charge were deprived of normal sleep patterns. 3-mile island, the Exxon Valdez oil spill, and the sinking of the Titanic all happened during the middle of the night, under the eyes of sleep deprived humans!