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Introduction
Life existed for a long time on earth before human intelligence. Does our planet just happen to be the only one whose conditions make life possible? Or are we one of billions of planets that sustain life? If little green men in flying saucers showed up, we could ask them the answer. But failing that, and without any conclusive evidence, we don’t really know.
The data we do have that we can examine is that life originated at least once here on earth very shortly after conditions appeared to be suitable to support it. More than three billion years after that, we humans appeared as a result of an almost uncountable number of life cycles, mutations, and reproductions.
This book is about the essential essence of humans as an intelligent life form — the nervous system. We can and do ask many questions about the nervous system, but here are three of the big ones:
What does our nervous system have in common with that of other animals?
How is our nervous system different from that of other animals?
What differences between humans are associated with differences in their nervous systems?
Neurobiologists have some answers to all three of these questions. We know that neurons are specialized cells with some functions specific to neurons, and others similar to most other cells on earth. We also know that nervous systems have similar organizational themes and methods of communication across all animal species. On the other hand, the nervous systems of mammals and primates are vastly more complicated than those of invertebrates and even of cold-blooded vertebrates.
