On my 70th birthday, I was asked how I felt about mankind’s prospects. This is my reply: We are behaving like yeasts in a brewer’s vat, multiplying mindlessly while greedily consuming the substance of a finite world. If we continue to imitate the yeasts, we will perish as they perish, having exhausted our resources and poisoned ourselves in the lethal brew of our own wastes. Unlike the yeasts, we have a choice. What will it be?