Then why did I see it in a mid-sixties SCIENCE TEXTBOOK?
Science textbooks, especially for the primary and secondary grades, are, with few exceptions, not written by scientists, but rather by professional textbook writers working for textbook publishers. They often don't really know what they're talking about.
I remember a series of articles in the mid/late 80's by William J. Bennetta (later of
The Textbook League). The state of California was considering new biology textbooks, so Bennetta recruited a panel of scientists to review the candidates. They found none of the books to be acceptable; they were full of errors, inaccuracies, and misconceptions. They presented a long list of necessary corrections that needed to be applied to the least terrible choice before it could start to come close to being acceptable. The publisher made a few of the corrections and then the board went behind the scientists' backs and approved the still-unacceptable textbook.
Creationist tactics post-AK/LA shifted to pressuring and controlling local school boards and to pressuring textbook publishers, but that's nothing new. After their "monkey laws" victory in the mid-1920's, they did the exact same things in the states where they didn't have those laws. And it was Arkansas' (one of the four "monkey law" states) adoption in the 1960's of a biology textbook
actually written by scientists which forced teacher Susan Epperson to file her lawsuit that let to the striking down of the "monkey laws" and set the "creation science" deception into motion.