In terms of mind/body discussions – there is a key distinction between the idea of neuroplasticity being the mind changing the brain, or the brain changing itself. The side question of how the human brain-and-or-mind developed is not the question here. Rather it’s the question: does ‘mind‘ = brain?
A simple analogy comes to mind (err… comes to brain… or… comes to mind+brain)…
I see the mind/brain question as directly analogous to the soul/body question. I am quite certain that any kind of non-physical mind we have will have more interaction/inter-section with our physical brains than, say, my underpants. In this sense, while rejecting a Platonic dualism between mind/brain, I do not reject at all a duality between mind/brain.
Those with the view that the mind is ‘nothing but the brain’ (and nothing at all!… never!… ever!… no possibility!… no discussion needed!… we know in advance!…) will say that neuroplasticity is ‘just’/’only’ the brain changing the brain. I think that view is a) reductionistic (hence the ‘just’/’only’), and b) un-necessarily so.
Again, I’m quite sure that neuroplasticity involves (at least) the brain, and I’m also quite sure that the toning of muscles through exercise involves (at least) the body. Neither of these certainties in any way are contrary to the involvement of either the minds role in neuroplasticity or the souls role in fitness.
Further, this is not an argument for some kind of (again) Platonic ‘ghost in the machine’ – that is dualism. Rather, it is an observation that a) we need not see humans (in their entirety) as only biological machines, and that b) a mind/brain (or soul/body) duality is perfectly harmonious with what we see the brain (or body) doing.