AFAIK
(a) It’s from interbreeding.
(b) It wasn’t always rape. Sometimes it was rape (assuming often), sometimes it was romantic, sometimes it was voluntary, sometimes it was ‘for something’, and sometimes it was prostitution, and sometimes prostitution was a business. And it was ‘taken for granted’ at the time. Which we find repulsive but historically was a norm. Example: The reason Muslim women wear veils originated in demonstrating they weren’t prostitutes, given that prostitution via slavery was a mainstay of the Islamic world. That demonstration became universal in the culture.
(c) just for humor: for all. Intents and purposes the races are species: phenotypical adaptation to local environments. The requirement for speciation is a bias in selection – not reproduction. However, humans’ evolutionary niche is adaptation itself, and humans (at least human males) are hyper-adaptive (meaning will have sex with things, animals, people, or anything at all). So human species (races) intermixed more often than other species, producing more hybridization, both with peers (sapiens sapiens) and will ancestors (Neanderthals, Denisovans, and possibly others.).
(d) While we know the single primary direction of human evolution (Neotenenic evolution, trading aggression and impulse, for extended childhood cooperation and self-regulation), contrary to postwar anti-Darwinian dogma, the differences between the races are substantial and meaningful, and we are only now learning of some of the goods and bads that come from hybridization. (See Reich’s lab’s research.)
(e) The evidence I’m carefully watching as it rolls out, is how much of this difference, most of which is a very minor variation that results in cognitive differences, results in increases in neuroticism or other cognitive or emotional errors.
(f) Yet it’s obvious that any intermixing between two races (neotenic generations of mankind, benefits the less neotenic class producing the results that are an admixture (average) of the two (somewhat).