When Carl Sagan published The Dragons of Eden
in 1977, his speculations on the development of the human brain drew on the still-nascent field of neuroscience. Now science writer Dorion Sagan (Carl's son) and brain theorist Skoyles present a follow-up that includes not only new discoveries about brain functions but also a coherent theory as to how and why humans developed the intelligence that sets them apart from other primates. Key to this evolution, they argue, are two facts: the plasticity of the brain (particularly in the prefrontal cortex), which means that it "is not fixed in what it can do"; and our status as social beings. Because the ape brain had already evolved into a "biocomputer with a wide range of mental skills that was ready, without further physical evolution, to do totally novel things," it could accommodate the need for pre-humans to use symbols to negotiate increasingly complex social relationships. And symbols "made the mind of the human-ape unlike that of any other," enabling its capacity for kinship, emotion and abstract reasoning. "Human evolution," Sagan and Skoyles argue, "did not fix our brain's information processing but instead created reprogrammable neural circuits that could evolve new kinds of intelligence." This thesis may generate controversy, but it is supported with creative arguments and intriguing evidence. Concluding with a sketch of how brain evolution might progress in the coming millennium, Sagan and Skoyles offer a thrilling, accessible biological narrative. (June)
