A normal human cell contains 46 chromosomes. Most tumor cells contain double or triple that; in some, chromosomes are also missing or mangled. The condition, called aneuploidy, was first linked to cancer in 1914 but the connection was eventually pushed aside when scientists (Duesberg among them) discovered oncogenes-- genes that spur tumor growth. If a few oncogenes mutate, the theory goes, uncontrolled cell division,
or cancer, will follow. But, Duesberg argues, the disease doesn't always follow. Scientists have genetically engineered rodents teeming with oncogenes and yet these animals, he notes, rarely become tumorous. "If the mutation theory was right," he says, "those mice should be meatballs." Moreover, cells within the same tumor don't always manifest the same mutated genes.