For scientists, finding agreement among several lines of evidence brings confidence that an explanation may have some validity. On the other hand, when different lines of evidence lead to opposite conclusions, this suggests that one’s hypothesis needs to be refined or rejected. A classic example of the latter situation comes, ironically, from what has been put forth as one of the strongest evidences for evolution--the wolf to whale hypothesis.
The evolutionary idea is that whales evolved from a terrestrial, wolf-like creature (a mesonychid). For some time, proponents of this idea advanced a series of fossil creatures that, they suggested, showed a series of steps between this mesonychid on one end and a whale on the other. Unfortunately, as scientists examine the morphology of whales, they realize that whales are morphologically more similar to pigs than to wolves. This is problematic in itself, but the situation is worse (for the evolutionist). Molecular information (DNA analysis) is also now available for assessing the wolf to whale story. It turns out that whales have a closer molecular affinity to hippos than to wolves.
Were* the wolf to whale hypothesis a valid explanation (for the origin of whales), one would expect to find agreement among the fossil evidence, the morphological evidence, and the molecular evidence. Instead, each line of evidence leads to a different conclusion, which argues against the validity of this particular story (best evidence though it may be for evolution).
* (“Were” is here used as the past subjunctive form of “to be” and should not be confused with the archaic word for “man” that, when combined with “wolf,” describes a mythological creature capable of transforming from a man to a wolf and back. This author will, however, allow the reader to draw his own conclusions about whether an inadvertent juxtaposition of these two concepts--werewolves and the wolf-to-whale hypothesis--is, after all, appropriate.)