"Of course there clearly had to be a Supreme Being. But since the universe was a bit of a mess, it was obvious that the Supreme Being hadn't in fact made it.
If he had made it he would, being Supreme, have made a much better job of it, with far better thought given, taking an example at random, to things like the design of the common nostril. You only had to look around to see that there was room for improvement practically everywhere.
Terry Prachett - Small Gods
If you had an opportunity to rebuild humans from scratch, what - if anything - would you change? Are we as good as we could be, or is there, in fact, room for improvement? Let's find out.