A knockdown prophecy

[Angrboda]

That's not how evolution works. With the exception of hybrids and a few rare instances like the marbled crayfish, no offspring is ever a different species from its parent. There was no first human, no first horse, and no first rabbit. Populations change over time as different alleles become more or less common. It doesn't matter how you define 'modern human', there wasn't a first one.

Sounds like a long winded way to say: I don't have a definition of "modern human", therefore there is no first human.

I mean, you're not wrong. If a characteristic X is undefined (or you can't define it), then there is no first element who has this characteristic.

Modern humanness is a matter of definition. Since the boundary of modern humanity is fixed by definition, i.e. fiat, rather than by fact, even if there is such a first human, it isn't a first human in any objective sense. Adam, however, according to scripture is objectively the first human. You're trying to fit a square peg into a round hole and aside from the unintentional hilarity of watching you try, it has no merit.