A knockdown prophecy

[Mister Agenda]

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.

No matter how you define it there was no first human or first modern human because the offspring is the same species as the parent.