Both models support the idea that populations of a plant or animal "type" can change through natural or artificial selection (such as dog breeding). The big difference is how much change can take place. Creation supports variation within a type (the Genesis "kind"), representing "good design" which allows populations to exhibit differing dominant traits in differing environments. Evolution believes that these smaller adaptations, given enough time, can eventually accumulate to become large changes, to the point where a "new type" of organism would now exist.

If evolution is true, the fossil record should show a continuous, gradual change from simpler life forms to more complex ones, with transitional forms existing in all cases. If creation is true, all higher-order forms (above the species level) were created fully functional and the fossil record should show abrupt appearance and no transitional forms. A "transitional" or "intermediate" form means a plant or animal which has some feature showing only partial development, such as "wings" that are part scale and part feather, documenting a transition from a reptile to a bird, for example. No such conclusive example is known, yet countless such cases must have existed if evolution is true! Note: a transitional form is often confused with a "mosaic", where an animal exhibits traits from different types, but where each trait is fully-formed. Mosaics are unusual but don't provide any proof for evolution.