Ah ha!!  I knew it.  Ladies, there is now a better excuse to get to bed early.  How about a scientific proof that yes, we really are that tired?  According to Yahoo! News:

"A study shows women normally wake up before men because they have shorter sleep cycles. The study found on average, women's 24-hour sleep-wake cycle is about six minutes shorter than men-- but due to sleeping and waking, that equates waking up about 30 minutes earlier.  It also makes women typically go to bed earlier than men.  It could also cause women's higher rates of insomnia and seasonal depression."

Read the full article HERE.

So ladies, don't feel guilty next time you have to "go to bed early" because you're tired!  It's natural.  But don't worry guys, that just may mean that your girl will wake you up a half an hour earlier to fit in "adult time"'...if you catch my drift. ;)