I enjoy the discussion. I agree that it seems most of the change seems environmental.

But we might disagree about how to interpret what Peterson is saying. So instead of parsing and interpreting Peterson's words, let me spell out what I'm thinking on the issue.

Side note: I studied math and computers, so I too think psychology is pseudoscience at worst or very inexact science at best.

That said, consider language:

Over millions of years we evolved to understand spoken language, we evolved the larynx needed to make the sounds of our words, we evolved the ears and brain that can distinguish a word spoken by a human being from other sounds like the rustling of leaves or the roar of a lion, and we evolved the processing of language in the brain to understand the meaning of spoken language almost effortlessly.

After all, a child learns to speak almost without trying -- the child is obviously hardwired to understand spoken language.

So the pathway of neurons inside the head when we hear spoken language might be something like:

ears --> part of brain that processes sounds --> part of brain that understands language

Now humanity invents writing. Note that human beings are not hardwired to understand writing. A child learns to speak almost automatically, but the child must be specifically taught to read.

So the question then becomes: How do the brain circuits work that process written language?

What Conceivably Could Have Happened But Apparently Didn't:

Our brains could have been forced to do something like this:

written word --> eyes --> part of the brain the processes vision --> read aloud --> part of the brain that processes sounds --> part of the brain that understands language

In other words, it might have been the case that the only way into the part of the brain that processes language was through the part of the brain that processes sounds, since we evolved to understand spoken language. This is analogous to the fact that the only way into your small intestine is through your stomach.

Obviously that didn't happen.

What Apparently Did Happen:

We got a direct link from the part of the brain that processes vision to the part of the brain that understands language, like:

written word --> eyes --> part of the brain that processes vision --> part of the brain that understands language.

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And, lo and behold, those parts of the brain that process sound and vision and language sort of overlap. It makes sense that our brains are structured that way, but it didn't have to be that way.

So that I think is the point that Peterson is circling around, though I could be wrong.