Scientific theories are never "true or "false"; they are "good" or "bad" in various degrees, and the criterion is one of usefulness—predictability and manipulation to (seeming) advantage. Theories are often discarded, simply because evidence may be insufficient for one, where it seems to sustain another—or where another can account for observed phenomena more simply. Take Lamarck's theories on the effect of environment on heredity; so far, the evidence seems to put this in the "bad" classification. But if certain experiments could be made....
