uses  now the reason we need, not just nuclear power of course, but all other sources of energy er is erm illustrated by these next couple of slides erm I'm sure you've seen data like this before  growth in the world's population over the last er few hundred years erm  over the middle ages the er world's population was fairly stable, although the birth rate was high er the death rate was equally high because of things like cholera and bubonic plague and smallpox and other things that used to kill people off in large numbers.