I sat down to read Marx (or maybe it was Engels?) a long time ago. I stood up again pretty soon. The same problem I've had with most of the German philosophers flattened me: endless, boring sentences stating the obvious.
(Well, maybe it was obvious. Or maybe I just got lost between verb and subject and the whole thing flew by miles over my head.)
Anyway, this is a long way of saying that it comes as a surprise to me that Marx owns the concept of facts taking precedence over ideology. And there, all these years, I thought that was merely logical.
Not saying anything against your main point at all. Biology deals in facts which don't even know you have feelings, let alone care about them. One of those facts is sexual reproduction.