I would argue no for the following reason: there exists a human who has the means, opportunity, and motive to procreate (i.e., another human to have sex with, a place to do so, and the intent to not prevent potential pregnancy) but does not do so because they have not enough viable sperm to penetrate the egg and commence gestation. I could object here, however, and purport that having the means to procreate implies viability of both one's reproductive mate and oneself, which weakens, if not nullifies, the above argument. An alternative explanation for why someone with the means, opportunity, and motive to procreate would not do so could be that they're a minor and, thus, "prevented" (quotes here indicatethis is a whole seperate argument that I'm not dealing with here) by paternalistic laws from doing so until they reach adulthood by which time the person no longer has the means, opportunity, and motive to procreate. The only way I would know how to show that procreation is not inherent to human existence would be by presenting a case for the existence of only humans without the means, opportunity, and motive to procreate, which I've been trying to do for the last hour and have yet to succeed... hopefully, this elucidates your question of why procreation is presumably presumable.
gravity matters to our lives on this planet.I think what you're hinting at though is an argument about ethical naturalism or rather the role nature has (if any) in informing morality, and then how we go about discovering nature and how we understand these discoveries. – virmaior Jan 26 '17 at 00:43