What was once the greatest mystery of biology, the human brain, is gradually yielding its secrets. Investigators are probing its deepest ＿＿（26）＿＿ with powerful tools. Francis Crick, who possesses a notoriously hard nose, has made consciousness a legitimate subject for science. Gerald M. Edelman contends that our sense of awareness stems from a process he calls neural Darwinism, in which groups of neurons compete with one another to create an effective representation of the world. Edelman has ＿＿（27）＿＿ this theory in a series of books in 1992. Others have challenged whether conventional neuroscience—despite its success in ＿＿（28）＿＿ other attributes of the mind—can ever account for consciousness. Chalmers rather holds that philosophers can and must construct a higher-level theory to bridge that “explanatory gap” between the physical and subjective realms. He asserts that just as physics assumes the existence of properties of nature, so must a theory of consciousness posit the existence of a new fundamental property. The field of consciousness studies is struggling with its own ＿＿（29）＿＿ problem.