You are correct; there is no shame in admitting what you don't know.
I know precious little about chemistry.
But, if my son was having difficulty with it, I'd begin teaching myself about it in a heartbeat so I could help him.
I don't have an issue with people who can't learn things. I have students like that all the time.
But, choosing not to learn about things because you have "no interest or desire" is quite a different thing, and quite unacceptable, in my opinion. And, I can't believe that you can't learn it since you have a university degree.
I just cannot understand it. You have quite a difficult situation with your son. If he needs you to understand biology and evolutionary theory, why wouldn't you do everything in your power to learn it and teach it to him?