life forms that can see stereoscopically (in "3D" or with two eyes, I guess) had an advantage over those that didn't.
That's quite clear. So, I understand that they first had to see in stereoscopy, and it was found afterward that this feature was giving them an advantage. But how could they see in stereoscopy in the first place?
evidence here that people should have learned in high school about biology.
You're right, my 2 kids are in HS upper year and I tell them that whatever they are taught re. evolution thay must learn so as to get good marks and their degree, it will be high time after that to make an opinion for temselves, because it is a domain which is open to opinion and beliefs, unlike gravity and rotundity of the earth.