A knockdown prophecy

[Mister Agenda]

No, there isn't.  Evolution doesn't work that way.  One could always say "modern humans have gene ABC, and pre-humans didn't", but then you would probably find some modern humans that don't have gen ABC either, and that gene might end up being found in some ancient hominids in some degree.

That's because you didn't accurately define what the word "modern human" means, once you stick to a definition, there is necessarily a first human who fits the definition.

But yeah, you always win if you keep changing definitions.

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.