We got to talking about climate history and human history. In Steffensen's view, these amounted to more or less the same thing. "If you look at the output of ice cores, it has really changes the picture of the world, our view of past climates and of human evolution," he told me. "Why did human beings not make civilization fifty thousand years ago?""You know that they had just as big brains as we have today," he went on. "When you put climate in a framework, you can say, well it was an ice age. And also this ice age was so climatically unstable that each time you had the beginnings of a culture, they had to move. Then comes the present interglacial--ten thousand years of very stable climate. The perfect conditions for agriculture. If you look at it, it's amazing. Civilizations in Persia, in China and in India start at the same time, maybe six thousand years ago. They all developed writing and they all developed religion and they all built cities, all at the same time, because the climate was stable. I think if the climate was stable fifty thousand years ago, it would have started then. But they had no chance. Under a White Sky: The Nature of the Future