No, not at all. You might also say that a marriage between a Frenchman and a Vietnamese woman might produce offspring with ancestors from those two regions of the world. It’s a little misleading however to ask (see opening post), “...what would happen if modern man and his prehistoric ancestor were to square off?” as it gives the impression that the ancestors of Homo sapiens are Neanderthals – they aren’t (although we carry some of their DNA).

Neanderthals might be better seen as our cousins, whose proper ancestor was certainly the same as ours - Homo heidelbergensis.