All they need to do is make this statement and the notion that God designed it is disallowed! No proof required. Ain't it wonderful how science works?
That is, by definition, the nature of science: natural explanations for natural processes.
As soon as you say, "God did it", then you are no longer scientific.
Of course, that doesn't mean you're wrong, it only means that science itself can't go there.
And if you'll give it a little thought, you'll realize that's just the way it should be.
After all, whoever would want some scientist defining what is, or is not, God?