do you need to know ios 7 if you want to program for ios 8?

Not really a programming question, but this topic needs an up to date discussion for all the newbies outthere. I've googled but didn't find anything useful. So, do you need to know ios 7 if you want to program for ios 8? Is iOS 8 just a extension and everything in programming for iOS 7 is also valid in iOS 8? There are many books on iOS 7(not so much on iOS8), but it would be a waste of money to buy out of date books. Thanks for answering