Or...modern humans walked out of the Garden of Eden (even if it wasn’t a literal garden and there weren’t literally two people in it) and the Neanderthals evolved from apes.
“and the Neanderthals evolved from apes.”
Neanderthals are always shown as basically football player Caucasians. Their extra brain size was apparently for a larger visual cortex. (location of size in skulls.) Their eyes apparently had no whites, meaning they were like modern ape eyes. (Eye genes genetically similar to apes.) So, they were most likely nocturnal and had much more developed visual capabilities. They most likely looked like apes and were probably covered with hair like apes. (They survived constant polar temperatures.) Most likely, we were not closely related and probably couldn’t interbreed.
Or maybe the Neanderthals were the result of hybridization, rather than evolution:
“There were giants in the earth in those days; and also after that, when the sons of God came in unto the daughters of men, and they bare children to them, the same became mighty men which were of old, men of renown.”
Since apes have one more chromosome than humans (two ape chromosomes are stuck together to make one human chromosome) that would probably be the big dividing line. After that happened, there would be little breeding across that line.
Homo Sapiens Sapiens and Homo Sapiens Neandertalis would both be on the same side of that divide.