THE BIRTH OF THE MIND
How a Tiny Number of Genes Creates the Complexity of Human Thought.
By Gary Marcus.
Basic Books, $26.
Gary Marcus, the psychologist who directs the Infant Language Center at New York University, wants to do something that would have been impossible a decade ago: reveal the genetic origins of the mind. Marcus posits that the brain is wired up by the genes to learn from its surroundings, a view considered extreme by many neuroscientists, who believe that experience determines the ultimate connections between neurons. In ''The Birth of the Mind,'' Marcus considers the common objection that the young brain's extreme flexibility means it requires sensory input to develop. Not so, he responds; the brain is prewired to be flexible, often, for example, sending test signals to confirm eyes and ears are working and to reapportion brain tissue if they are not, even while still in the womb. Marcus writes that the brain results from the same pathways that make lungs, noting that ''from a gene's-eye view, brains are just one more elaborate configuration of proteins.'' When it is not bogged down in the nature-nurture debate, ''The Birth of the Mind'' presents a clear and accessible review of recent work on the biology of brain growth.