Subtitled "Speculations on the Evolution of Human Intelligence," [The Dragons of Eden] is a superlative work: erudite, facile, fascinating, and eminently readable. In it, Sagan "speculates" about what is going on inside the human head. Fundamentalists had better not get into this book; it's liable to cause a fundamentalist fit. Central to Sagan's speculations (which qualify him as a latter-day "Renaissance man," so wide is his range of references) is the fact of human evolution from earlier forms of life on spaceship Earth.

In order to say anything about what might be going on between our ears, Sagan has to describe the process of brain evolution. (p. 88)

Sagan devotes a good deal of attention, of course, to the neocortex [a part of the brain common to most higher primates], especially the left and right hemispheres and their distinctly differing functions. He not only restates the "basic" information now...