Ruby, embarrassing to say, but I haven't read either Dawkins or Kant. My opinon of DST is based soley on a quick read of wiki. There may be more there. As soon as I hit the "not testable" line, I admit, I lost interest. I want to discoveries of how we are made and how we got here to continue and that can only come by relentless inquiry. I enjoy the complex mathematical models that pit various scenarios, say, at selfish and altruistic reproducing blobs. I wish I could find a video to demonstrate. Thanks to computer modelling, the mathematician can set the model to reproduce for generations and see what comes out. Influences like environment do have an effect on the outcome. We do live in a complex environment.
About losing unused brain power. I wish I did not have examples. But we know that if an infant does not acquire language by age three, their ability is impaired permanently. A person without the power of language does not have an inner dialogue to anticipate, evaluate scenarios, or to plan. It's gone.
On the other hand, we have underestimated the brain's generative power and it's ability to repurpose sectors of the brain for new use (neuroplasticity). Stroke patients who receive intensive therapy can regain a great deal.