Why do zebras have stripes? and why is a giraffes neck so long? and why did these species survive past darwin?

You have to understand that the phrase 'survival of the fittest' does not have to imply that what makes an animal fit is obvious to you. On the Giraffes they would have an obvious advantage of being able to reach food high up in a tree that other animals are unable to reach. This means that they may be able to survive even during droughts. As for the zebra/stripe thing I cant begin to guess how that might help them survive.