Good question. You could say it's biblical literalism, and a concern with human uniqueness. Those are both probably part of it, but it's not that simple.
For instance, as I've pointed out several times, the Bible affirms in many passages that God is intimately, personally and directly involved in the creation of individual humans; not just the species, and not just Adam and Eve. This includes "forming" and "shaping" the "inward parts" of humans in the womb, and "knitting them together of bone and sinew". (Excuse possibly not exact quotes from memory.) Yet you never, ever hear a fundamentalist complain about human embryology being taught as a strictly naturalistic discipline.
Please dont give them any ideas.