AP Photo

Compact and white-haired at 75, Peter Duesberg has wide-set blue eyes magnified by corrective lenses as thick as his German accent. He is the picture of a courtly Old World scientist. But Duesberg is given to through-the-looking-glass scientific theories, the most recent of which, about the origins of cancer, could turn an accepted truth of molecular biology on its head. Viruses like hepatitis C don’t cause cancer, he says, and neither do collections of mutated genes — as nearly every other scientist believes. Instead, he argues, cancer arises when the number and appearance of a cell’s chromosomes become disrupted, leading to a tumor that has, in effect, evolved into a parasitic new...