Evolutionary theory says that the fittest survive. How do we know which are the fittest? Well, they are the ones that survive.
I am not a fan of evolutionary theory, but at least one attack on the theory is pointless. Some people argue that evolutionary theory is wrong because it is a tautology. Of COURSE it is tautological. All of science is tautological because all science is based on math and all of math is tautological.
Tautology is extremely important - it shows us that things we never suspected were the same ARE, in fact, the same. So, a really complicated equation may turn out to reduce to 1. Who knew? It was a very informative tautology.
The problem with evolution theory is it tends to be uninformative tautology.
BTW, creationism is also useless, just in a different way. I have no no idea how God populated the earth with living things, nor is it central to my salvation that I know these things, so it isn't something I view as a crucial problem to solve.
The primary point of this post is to point out that tautology, per se, is not the problem.
Uninformative tautologies - those are the problems.