I’m not speaking developmentally but evolutionarily. A fetus is human from the instant of conception.
It’s pretty obvious that whatever Australopithecus is, it isn’t a human being.
And it’s pretty obvious that Sumer is the dawn of humanity as we know it, with religion, agriculture, commerce, art, music, poetry, history.
In between you have creatures that are hard to classify right now. What I mean by not “full-fledged” humanity would be putative human-looking beings who were not descended from Adam and Eve. Augustine casually mentions the possibility of such races in his discussion of the Antipodes.
I tend to agree with your theological views, but your science is a bit off. There were modern humans of species H. Sapiens long before Sumer. Modern humans first emerged about 300,000 years ago according to the best available scientific evidence, and this occurred in Africa, not Sumer. Sumer is generally accepted as the first example of civilization, which includes among other features the presence of a written language, a centralized government, and extensive agriculture. It’s not correct to state that the people of Sumer were the first humans, however.
Excerpt from Augustine's "On Genesis"
Book II "Question of the phase in which the moon was made" 15, 30
"God, after all is the author and founder of things in their actual natures. Now whatever any single thing may in some way or other produce and unfold by its natural development through periods of time that are suited to it, it contained it beforehand as something hidden, if not in specific forms and bodily mass, at least by the force and reckoning of nature, unless of course a tree, void of fruit and stripped of its leaves throughout the winter, is then to be called imperfect, or unless again at its origins, when it had still not yet borne any fruit, its nature was also imperfect. It is not only about the tree, but about its seed also that this could not rightly be said; there everything that with the passage of time is somehow or other going to appear is already latent in invisible ways. Although, if God were to make anything imperfect, which he then would himself bring to perfection, what would be reprehensible about such an idea? But you would be quite within your rights to disapprove if what had been begun by him were said to be completed and perfected by another."