Great explanation. Kudo
However, for "timeworn yarn", which means indeed an effete story, yarn at most is not another idiom but at most a synonym
story=plot=yarn=tale and blah blah blah.
Moreover, has been turned on its head (not it's) means
not shown to be true .
Once again, you gave a really in-depth and well-rounded explanation. And this is great. But the first sentence as per reading
What tradition has long known, science must labor through its usual rigorous protocols to arrive at the very same assessment means only and one only reason:
the science has to work really hard to arrive at the same conclusion that philosophers and thinkers - think about for instance to the stoicism: it teaches us things that the modern psychology now is confirming totally and Marco Aurelius was the Emperor of Rome 138 BC - already knew.
So for me, the second sentence should confirm this trend that the babies DO NOT passively receive the stimuli from the outside world and that they conduct experiments (very much like the scientists themselves) ALTHOUGH they do not master totally. This idea is also to be noted at the very end of the entire sentence where the environment explored by the babies themselves is
enchanting and frustrating at the same time.
Anyhow, great discussion: we should have more of this on the board.
Thanks for the depth of your explanation. I came to the same conclusion that you did. I hope that the GRE experts reason as you do.
Thank you so much.