The philosopher Epictetus taught that you should avoid troubling yourself about matters not within your control, and exert yourself toward things that are. (The book of Ecclesiastes has the same advice, BTW.) Maybe that’s only “dumb” with a college education, but it’s still excellent advice.
It is true, however. A recent book, “The Shallows”, reviews the history of how the human brain has evolved to receive and process information, from the invention of writing and the earliest alphabets to the present day. In the context of what we’ve learned about neuroscence, each new invention has physically rewired the human brain, so that areas of the brain supporting older skills that are no longer used regularly — the verbal memory needed in a preliterate society, for instance — actually atrophy. They may not be unable to be regained, but the loss is real enough. (The book is readable and compelling; check it out.)
Whether this is enough to qualify as “stupider”, well….
Why is this surprising? The whole point of religion — any decent religion — is to help you get there, by showing you the truth about yourself, and how you relate to those around you and to God. But religion is like training wheels: once you get it right, it’s no longer necessary. (St. Paul said something much like that in Galatians, IIRC.)
You and the rest of the human race, bro. My mom, who passed at the age of 99, told us that the experience never goes away.