Well, I'm pretty sure the evolution of the sex monkey has more than a few lurid episodes of hybridization, not only amongst those still in Africa , but along the paths of the exodus as well, both northerly and eastward. And rather than singular migrations it surely must have been a nearly continuous outflow of any number of hominid species present at a given time. And as the species shifted, they would no doubt encounter remnant populations of previous groups that had settled along the way while others of these previous groups continued outward and beyond. And more than likely, hybridization was an ongoing occurrence along the routes.
There's the evidence of an ecosystem akin to the African Savannah up in the steps of Eurasia replete with a wide variety of migratory hoovestock which could have very well fed a growing population of early hominids until it died off or was hunted out of existence.
The fossil record is so very incomplete, so there's little likelihood that we'll find evidence of all the various forms of hominids,nor a sufficient amount to begin to recognize the transitional hybrid forms which themselves may have led to new species still waiting to be found.
And then there's the transformation of those that became H.floresiensis, or which there is no linking evidence, yet as a member of Homo, it's unlikey they started out at so diminutive a size, but rather reduced their stature over time as a result of insular living.
tory
But all in all, I think it's a pretty safe assumption to think there was a LOT of hybridization going on across the migratory routes, with most of the "outliers" genetic contributions simply getting integrated into the whole.
Above, Chim Chim asked after all what is a modern human? Perhaps far more of a composite of previous forms than we 're comfortable admitting. Once the basic format was laid out and interbreeding proved viable, nature kinda went off experimenting, trying out different combinations, finally reaching a versatile and highly adaptable "species" which then integrated(sexed into genetic extinction)the few remaining forms unable to effectively compete yet still ( "hey baby!" ) walking upright!