A knockdown prophecy

[Angrboda]

This is devolving into a cheap game of semantics. Even if I play along, I can still squeeze a first modern human from your description above, regardless of its accuracy.

Let's assume we observe the first generation of modern men dispersed over groups in different places around the globe.

Step 1 : For each group of "modern men", take the oldest member.

Step 2 : You get a collection of very old people, each of whom would locally be considered the first modern human.

Step 3 : Take the oldest element in this collection. This element would evidently be the first modern human we're looking for.

QED.

The existence of a greatest element is a mathematical property about finite sets, the set of modern humans is finite, people.

Let me put the problem to you so that even you might understand. Let's say we have scientist A and scientist B who use different definitions of modern human. According to A, specimen #1264 is the first modern human. However, according to B, specimen #12,831 is the first modern human. Neither is objectively right or wrong, they're both equally right and equally wrong. However, since A and B claim different specimens as the first modern human, there is no fact of the matter as to which is the first modern human. It's dependent upon which definition a person holds, and as such it depends upon a specific mental disposition and is by definition subjective. Subjective facts are not objective facts and ne'er the twain shall meet. But do keep trying. It's good for the lulz.