Modifying DNA and playing with genes biologists create all kind of mutations - those which are similar to "natural" mutations and well beyond. They accelerate evolution many folds, or reverse it (by removing genes or entire chromosomes).

Analysing genotype of various species, again they find direct correspondence between gradual/abrupt changes in DNA and gradual/abrupt changes in body design/function from specie to specie (and within species).

The similarities in DNA found in different species is strongest evidence of evolution - because it is impossible to have similar DNA "by chance". Only common origin creates common DNA.

Rate of evolution follows rate of changes in environment. Some marine animals did not change much over a few hundred million years (many millions of generations), yet some bacteria and viruses may change dramatically in a few tens of generations only. So sometimes creating "new" specie takes hundred million years, sometimes - few years or tens of years only (thus leaving very little fossile record and appearance of abrupt changes). So, abrupt changes in environment (asteroid, volcano, runaway climatic instabilities, viral deseases, etc.) may result in abrupt changes of specie due to survival of only extreme mutants.

So, it is not a question of "evolution (=selection) or ..." (ahem, or WHAT instead of evolution by the way? What is the alternative? Creation? Of human with 98% of ape DNA?), it is a question of clarifying details of natural selection in complex and changing environment.