i strongly suspect that it's the act of actively becoming a parent, whether biological or adoptive that is responsible for that change in hormones
For this context, I think trying to make these distinctions is a distraction. By way of common sense, reproducing & parenting has been a HUGE factor in the propagation of human life (this is so obvious it's kind of funny to write).
So basically you don't want to have a discussion that might make you reconsider your belief.
To me, this makes sense, given how unusual the new skillset has to be compared to pre-fatherhood life (manipulations with the newborn, deciphering needs, new attetion patterns etc.).
[1] Mentioned in the book by Stanislas Dehaene, "Consciousness and the Brain", https://en.wikipedia.org/wiki/Consciousness_and_the_Brain
Allow me to disagree. First: there's no evidence of any change in your body, as a male, after becoming a father.
Second: supposing such a "wireless" change would happen, getting someone pregnant and immediately disappearing from their life would yield a perceptible change even with distance and no involvement with the life of the child.
Third: I personally think there's no innate drive to parent, and only an innate drive to mate; everything else is injected by society.