... events, and responds to them, often by restructuring the genome. We know about the components of genomes that could be made available for such restructuring. We know nothing, however, about how the cell senses danger and instigates responses to it that often are truly remarkable." Thus Barbara McClintock ends the paper she delivered in Stockholm when she received a Nobel Prize in 1983. Most of McClintock's paper reviews her pioneering work with the corn genome, but she adds some examples of other genomic responses to external stresses. One such stress is applied to an oak tree when a wasp lays its egg in a leaf. The stress causes the oak genome to reprogram itself and construct a wholly new and unplanned plant structure to house and feed the developing insect. Some of these structures (galls) are very elaborate and are precisely tailored to each different wasp species. From such examples, it is apparent that the genome of an organism somehow perceives stresses and reacts to them -- often in completely unanticipated ways. The stresses may be mechanical, thermal, chemical; in fact, almost anything. McClintock's conclusion is: ". .. that stress, and the genome's reaction to it may underlie many formations of new species." (McClintock, Barbara; "The Significance of Responses of the Genome to Challenge," Science, 226:792, 1984.) Comment. The implications here are broad and deep. Evolution can be driven by external stresses. The new species thus produced may differ substantially from the original organism, eliminating the need to ...