Speech enables man to manage and exchange ideas, and it also allows him to collect ideas. Once spoken and heard by another, an idea gains lasting qualities. Speech and writing permit man to gather together thousands of years of ideas. A young chimpanzee can obtain information only from those it associates with, but a human child can inherit all the knowledge that has been gathered for two million years. Man learns from the past and builds on it. The ape learns from the present and repeats it. If man were as unable as the ape to exchange ideas, he too would still be building nests in the trees.