Whatever the reason, the changes were powerful enough to disrupt the weather all over the world, including in our African birthplace. But not too powerful, or too subtle—a phenomenon called the Goldilocks Effect. If the changes had been too sudden, the climatic violence would have killed our ancestors outright, and I wouldn’t be writing this book for you today. If the changes had been too slow, there may have been no reason to develop our talent for symbolism and, once again, no book. Instead, like Goldilocks and the third bowl of porridge, the conditions were just right. The change was enough to shake us out of our comfortable trees, but it wasn’t enough to kill us when we landed.

Whatever the reason, the changes were powerful enough to disrupt the weather all over the world, including in our African birthplace. But not too powerful, or too subtle—a phenomenon called the Goldilocks Effect. If the changes had been too sudden, the climatic violence would have killed our ancestors outright, and I wouldn’t be writing this book for you today. If the changes had been too slow, there may have been no reason to develop our talent for symbolism and, once again, no book. Instead, like Goldilocks and the third bowl of porridge, the conditions were just right. The change was enough to shake us out of our comfortable trees, but it wasn’t enough to kill us when we landed.