I think math and science clash here. Math would prove that Darwin does not explain evolution. The survival of the fittest is true. But the speed of DNA change cannot explain evolution. Change is too slow and random for it to explain the speedy change in species.
Genesis could have happened. Just not here on earth.
It's true because it's nothing more than a tautology. "Only the fittest survive and we know that because those that survive must be the fittest because they survived."