With the world's advances in medicines and technology, we are able to keep many people alive who would have died in years gone by.  This is, of course wonderful when we look at it from a "life is all important" view point.  BUT, what will happen in the world with more people?  Where will the additional food and water come from?  How can we sustain an increased population?  Begin with and think about the problems - do some research come up with your ideas.