RICHARD TOWNSHEND/CORBIS

Textbooks usually make the triumph of a scientific theory seem inevitable and uncontestable. But at the time that a theory is being forged, the reality is not nearly so tidy. An experimental result is only clear-cut if researchers agree on how to interpret it. Individuals may have conflicting hunches about what nature is up to, however, and a finding that is conclusive to one scientist may be unimpressive to another. In some cases the ideal experiment is not yet possible. In others only one or a few data points exist. Disagreement is productive, though. It forces each side to clarify its views and to find experiments that will distinguish one idea from another. And in the end, researchers generally come to a new consensus. Experiments corroborate each other. Theories make defensible predictions. And new students come along who lack the prejudices of their predecessors. Science marches ahead, in other words, erasing many records of dissent along the way. Here are six raging debates that textbooks will one day no doubt present as cut-and-dried. --JR Minkel