Homo erectus, also known as the Neanderthal tribe, coexisted with the Cromagnon tribe (which became modern man) for quite some time. Later, when Cromagnon found out that Neanderthal was
Homo erectus, Cromagnon, being very bigoted in those days, wiped out Neanderthal, or, at least, that is the majority
opinion.
A minority opinion is that some
men of the Neanderthal tribe married women of the Cromagnon tribe so as to blend in, while hiding their true nature as
Homo erectus. Maybe they closed their eyes and/or turned off the lights, and imagined they were having sex with other
Homo erectus, no one knows for sure. According to this opinion, the
Homo erectus still live among us as a genetic variation even within otherwise Cromagnon families. Sometimes Homo erectus
will even marry each other, but, like most hybrids, they are unable to reproduce with each other, making them dependant upon Cromagnon in order to have natural children.