When we had to survive on our wits, gather and kill our food from scratch and be more at the mercy of our environment than we are today, we probably had enough challenge to keep our brains healthy.
Within a hundred years of physical and chemical science, men will know what the atom is. It is my belief when science reaches this stage, God will come down to earth with His big ring of keys and will say to humanity, 'Gentlemen, it is closing time. '