THE ASTONISHING HYPOTHESIS

It's exactly 40 years since Watson and Crick published their landmark double-helix papers in Nature, setting biology on a revolutionary course. In the meantime, Watson has continued to reign supreme in matters genomic, while Crick (now at the Salk Institute) has pursued lifelong interests: the origin of life and the nature of the brain. Lest anyone doubt, Crick hasn't suddenly got religion; the ``astonishing'' of the title refers to his reductionist conviction that we're merely a reflection of how our nerve cells behave. As for soul, this is a book about consciousness: Soul hardly enters in except by way of denying mystical entities, ghosts, or other personae in the machine. Moreover, Crick omits discussion of self- consciousness and uses visual awareness as his surrogate for consciousness in general. His reasons are that humans are strongly visual animals; that much is known about the visual system in primates and humans; and that many experiments have and can be done to test hypotheses. So after some introductory historical material, he plunges into several hundred pages of review on the organization of the brain and the visual pathways. None of this is likely to entrance readers outside of neuroanatomy classes, but at least one point is well taken: Computer folk won't get anywhere trying to model the brain with digital approaches—the brain is a super parallel processor that ``degrades gracefully'' (it can afford some loss of neurons without ill effects) compared with ``brittle'' PCs. In the end, Crick (as well as CalTech colleague Christof Koch) sees the virtue in some neural network models and argues that the brain's thalamus may be the central integrating unit in consciousness, with the process perhaps requiring some aspects of memory and attention and involving synchronous firing of groups of neurons. These are plausible, interesting, testable ideas—but, as Crick admits, there's a long way to go.... (Ten b&w photographs, 60 drawings—not seen)