Interesting .. but I think what has been described as Darwin's "doubt" might actually be Darwin's joke. Plantinga is taking something said tongue-in-cheek, and applying formal logic to it .. it's fun, but not that worthwhile.
The fact that our physical brains are the product of natural selection, and are in a constant
state of evolutionary change, does not make them unreliable - the mind .. that difficult to quantify product of the electro-chemical processes of the physical brain, and what we do with it, is quite separate from what was occurring within the distant relative that was our original monkey brain. :)
Philosophy, including logic, as well as mathematics and the scientific method, is what gives our 'minds' reliability. Observation, how we "see" the world around us, might be a physical process, but the way we determine reliability is that others see the same things we do, and then we apply evidence-based reasoning in order to come to the conclusion that what we are seeing, and what it means, is "probably" correct.
In the end, this is all that we have, so we must consider our conclusions to be correct - Darwin was living in an age of great science-based wonders, discoveries and creations, and that is why I believe that his "doubt" was a joke .. the reliability of our monkey-brain was being proven on a daily basis .. medicine, engineering .. a long list - around the time of his authoring "The Origin of Species", electrical light was beginning to roll out to the public and all things electrical was all the rage .. proof of advancement! :)
I leave room for the existence of a creative force in the universe, and even the possibility of a designer responsible for us, but if there was / is such a being, I believe it dictates and directs nothing, but rather introduced an evolutionary algorithm that has led to the diversity we see, and has resulted in us, and what we in a constant state of becoming. If that is not the case, then it is all just dumb luck and responses to environments that were randomly generated by natural forces. :-)
All very interesting .. and I am no expert in any of these areas, but I really appreciate the reply .. it's great that such conversations can carry on, on STEEMIT!
Cheers!