It's a definitional thing. By "evolution", most people are referring to Darwinian models rather than Lamarckian ones, but there are quasi-Lamarckian models that are actually quite plausible.
Selection is pretty clear cut. The biggest argument (to me) is identifying what the major source of variation is. For strict Darwinians that is usually "mutation", but other possibilities exist.
Indeed, that is the reason for these threads, other possibilities exist. One such is that species were intelligently designed by a Creator.
Since neither of these possibilities has been observed one must try to deduce from available evidence which is the more likely of the two. The discovery of DNA has scientifically shown the unlikelihood of mutations being able to achieve the large transformations required for evolution to be true. Intelligent design by a Creator is therefore the most likely of the two possibilities.