I'm not denying that we can make presuppositions. I'm questioning their rational basis under the two respective worldviews of atheism and Christianity. I am not dealing with other worldviews right now - only those two.
(Yes there are so-called "theistic evolutionists." My reason for selecting atheism is because I thinkg that Darwism fits most consistently into that particular worldview, as Darwinism attempts to provide a rational basis for it, e.g. a way to explain our origins without God).
"Darwinism attempts to provide a rational basis for it, e.g. a way to explain our origins without God"
False. If it did, it would violate methodological naturalism. Science is philosophically removed from arguments for or against God.
"I'm questioning their rational basis under the two respective worldviews of atheism and Christianity. I am not dealing with other worldviews right now - only those two."
But, that premise is false as evolutionary theory is not atheistic. Also, philosophical propositions do not affect the reality of the situation. This is why Greek science died - it's not enough to construct logical arguments for or against something; you have to actually go investigate.
For example, quantum mechanics entirely violates causality or cosmological arguments. The philosophical irrationalities though do not render quantum mechanics false because such philosophical propositions are self-consistent axiomatic fields that do not necessarily hold true in the world.