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.