A bronze of Rodin's The Thinker Copyrighted image Credit: Jupiter Images

We separated from our Old World monkey cousins some thirty million years ago, and from the chimpanzees some six million years back. The brain has evolved in this period in response to environmental and social changes. The basic impetus is always the same- the individual gene seeks to perpetuate itself.

Genes become associated in body systems and many species enhance their survival with collective living and communication.