Natural Selection Seems Insufficient

[Jal]

Bullshit. That's a non-sequitur.  Or false dichotomy. Or some other fallacy.  "Humanly undetectable" doesn't translate to impotent. Many things were humanly indetectable until modern science.

You're underestimating God's ability to play hide and seek.

Don't overcomplicate this. God simply loves His clay dolls.

LOL, "humanly detectable".  Nothing that we've now detected was ever impossible for us to detect, as you suggest these souls are, just undetected.  You could only be talking about a thing that doesn't interact.  Consider this, even if your god made a soul shaped hole...by magic....we could detect the hole.

That's a reasonable argument, but isn't necessarily how things work. The soul's principal influence on the body is to animate (i.e. push/ pull it).

For example suppose I hunger to throw a punch. My body, left to itself - limited to the Universe's blind causality/ domino effects - wouldn't likely move my fist in that direction.

At this point free will  - a self-propelling soul - drags my fist toward the target. By default, a scientist would be inclined to attribute the motion to muscular activity such as ATP. How would he identify an invisible soul at work here? And even if he found an instrument to do it, how can you be sure that God won't hide it from the instrument by skewing the results?

I'll say it again: You're underestimating God's ability to play hide and seek.