She was asking who the first Homo Sapiens was. I suggested that if there was such a person, if an anthropologist had been there they wouldn’t have seen anything special happening. The way they would have categorised hominid species would depend on the populations they saw at that time.
It’s the same with civilisations. How we categorise them is temporally dependent and is in fact an artefact of language. Reality doesn’t care if our linguistic categorizations make sense, or how they are limited.
There is no such person. Speciation isn't some quick and dramatic happening, it's a generally slow evolution (though a lot faster for things like bacteria). "Species" is just how biologists categorize things, but organisms are continually evolving to some extent, so if you grab some random humans from 1M years ago, and compare them to random humans today, you'll find some pretty significant differences most likely, even if it is possible for them all to interbreed. If you go back even farther, the differences will be greater, you might not be able to interbreed, but there's no clear delineation if you look at humans and their ancestors over the course of the last ~5M years, just a slow progression. Our modern biologists/anthropologists make up names for the beings from various select points in time, since they do differ markedly from beings at other far-removed points in time, but we don't have a clear picture anyway because all we have is fossils which don't show a clear picture, they're just select points in time where we got lucky and were able to find an artifact.
Similarly, analyses like these cannot help but be a reflection of the society that produced them. This article features a callout in the middle with weirdly axis-ed charts about climate change, inequality and environmental degradation, it's difficult not smirk knowing that within the context of our current society, there was no way it could be otherwise. One wonders 50 or 150 years ago what the cultural bugbears were and what the callout in the middle of the page would have featured. Overpopulation? Nuclear war? Out-of-wedlock births?
Even if you just want to look at who controls rome (understandable if we're talking about calling something the roman empire), after the reconquest by Justinian, it belonged to the eastern empire about the same amount of time as the west.
There's also the medieval Holy Roman Empire which was officially a continuation of the Western Roman Empire, and at odds with the Byzantine Empire because they considered themselves the only legitimate Roman Empire, and these are all related but clearly different cultures.
And then there's the vikings which were clearly a different culture, arguably a different civilisation, but infused themselves in every corner of Europe, from England to Russia to Sicily and Byzantium.
Civilisations do not have clear boundaries, both geographically and temporally, and you certainly can't equate them with empires. I think civilisations rarely truly collapse (except under the impact of invasion or colonialism maybe), but they do change, and sometimes dramatically. The collapse of empires is sometimes dramatic, as in the case of the Western Roman Empire, and sometimes barely noticeable, as in the case of the Holy Roman Empire.