We are part of nature, a product of a long evolutionary journey. To some degree, we carry the ancient oceans in our blood. … Our brains and nervous systems did not suddenly spring into existence without long antecedents in natural history. That which we most prize as integral to our humanity - our extraordinary capacity to think on complex conceptual levels - can be traced back to the nerve network of primitive invertebrates, the ganglia of a mollusk, the spinal cord of a fish, the brain of an amphibian, and the cerebral cortex of a primate.