One of the main problems when skeptics like yourself get involved in specific issues involving the immaterial (in this case “How does evolution affect the traditional theological concept of the soul?”) is that the discussion can end up ignoring the actual question and trying to defend or attack the very existence of the immaterial itself. Interesting, but diverting from the matter in hand.
For the person committed solely to scientific evidence, no evidence for the immaterial can, in principle, be found. It is simply impossible for the activity that investigates material efficient causes to draw conclusions about what is not material, like (in Ed Feser’s example) sweeping a field with a metal detector and declaring there is no architecture or pottery buried.
The other side of the same coin is that material processes cannot, in principle, produce non-material outcomes. So as I hinted above, to investigate evolution for clarification on “the soul” is a wild goose chase. If non-material elements exist in human beings then Darwinian evolution alone has no way to produce them, and I include in that formal causation in the Aristotelian (not Platonic) sense and final causation in the Christian sense.
An agnostic open to other sources of knowledge may well find plenty of empirical evidence for the immaterial: my “no-religion” son-in-law, some years ago, found himself saying when the phone rang, “That will be my mother telling me my grandfather’s died.” Grandfather was previously well, mother didn’t often phone - but it turned out he’d unexpectedly taken his own life. Most people have some such anomalous experience which they refuse to reject even if they don’t understand it. Sometimes they do understand it - somebody recovers suddenly from illness at the time they later discover their Church prayed. The empirical evidence can be assessed in such cases - but evaluating it through science cannot conceivably endorse any immaterial cause.
So this discussion ought to proceed in the context in which Brad set it: “as modern Christians”, that is, accepting the assumption of the immaterial, in that we are doing theology from belief in God, or it is going off-topic.
If that is so, right ways to investigate “the soul”, it seems to me, are ways that are capable of dealing with the immaterial because they themselves involve the immaterial.
And so it is legitimate to address it, as those like Aquinas or even Plato did, from purely philosophical reasoning, since logic is itself immaterial. Is there a logical necessity for the soul, and what characteristics must it have if so? That involves the same orderly mental processes that are used in science, but which precede it and develop the metaphysical basis on which science can be done. But they are more versatile than science, though they include it.
Secondly, it is legitimate to involve the other half of intelligence, intuitive reasoning, just as scientists do all the time (though it’s a well kept secret, cf Kuhn, Eddington, Polanyi etc). Intuitions seldom stand alone, but provide the insights to be tested by other means.
Thirdly, divine revelation is essential in an area for which, though we have direct experience (we know we are “us”, for which there is no persuasive material explanation available) we cannot fully know ourselves. What does inspired Scripture say about souls? How does it relate to cultural milieu (and how does the cultural milieu relate to true knowledge, because even ancient Egyptians might have good insights)? Importantly, does it encourage us to bother with the issue, or suggest that we spend our efforts on other matters?
I’ve not made any positive contribution to the actual matter in hand with this, but here’s a thought. Resurrection is the firm Christian hope: Abraham, Isaac and Jacob will be at the wedding feast of the Lamb. That implies there is a principle of continuity, technically a “universal” of human identity. One could place that in God’s mind, so that he somehow recreates us as us - that makes it akin to a platonic form, re-instantiated in new matter. A bit like a soul. Or this universal could reside in our constitution, in which case if you don’t call it “the soul” you call it the same thing by another name.
But it doesn’t reside, by any means I can conceive, in anything to do with Darwinian evolution.