Originally posted by Coletti
Falsifiability.
There must be some criteria which you can say would disprove the theory. If X is true, then theory Y is false.
Evolution is a theory, not a hypothesis, because it has survived repeated tests. You have managed to define evolution's strength, not its weakness.
However, Creationism as a general theory fails on this very criterion of falsifiability. In defense of their general theory, Creationists do put forth propositions that can be tested from time to time, and their work demonstrates a long string of failures.
Consider as one of hundreds upon hundreds of examples:
"The reptile-bird intermediates mentioned above date from the Upper Jurassic and Lower Cretaceous (about 150 million years ago), whereas pelycosauria and therapsida (reptile-mammal intermediates) are older and date from the Carboniferous and the Permian (about 250 to 350 million years ago, see the Geological Time Scale). This is precisely what should be observed if the fossil record matches the standard phylogenetic tree.
The most scientifically rigorous method of confirming this prediction is to demonstrate a positive corellation between phylogeny and stratigraphy, i.e. a positive corellation between the order of taxa in a phylogenetic tree and the geological order in which those taxa first appear and last appear (whether for living or extinct intermediates). For instance, within the error inherent in the fossil record, prokaryotes should appear first, followed by simple multicellular animals like sponges and starfish, then lampreys, fish, amphibians, reptiles, mammals, etc., as shown in Figure 1. Contrary to the erroneous (and unreferenced) opinions of some anti-evolutionists (e.g. Wise 1994, p. 225-226), studies from the past ten years addressing this very issue have confirmed that there is indeed a positive corellation between phylogeny and stratigraphy, with statistical significance (Benton 1998; Benton and Hitchin 1996; Benton and Hitchin 1997; Benton et al. 1999; Benton et al. 2000; Benton and Storrs 1994; Clyde and Fisher 1997; Hitchin and Benton 1997; Huelsenbeck 1994; Norell and Novacek 1992a; Norell and Novacek 1992b; Wills 1999). Using three different measures of phylogeny-stratigraphy correlation [the RCI, GER, and SCI (Ghosts 2.4 software, Wills 1999)], a high positive correlation was found between the standard phylogenetic tree portrayed in Figure 1 and the stratigraphic range of the same taxa, with very high statistical significance (P < 0.0001) (this work, Ghosts input file available upon request)."
Theobald, Douglas L. "29+ Evidences Macroevolution: The Scientific Case for Common Descent." The Talk.Origins Archive. Vers. 2.83. 2004. 12 Jan, 2004 <http://www.talkorigins.org/faqs/comdesc/>