Wow you are dense. I didn't say anywhere that we don't breed. But Humans don't need to worry about passing on any traits that are bad for living in the wild simply because we don't live in the wild. We change the environment to fit OUR needs, not the other way around, like every other animal. So inheriting legs that aren't the best suited for running isn't going to cripple our race like it would wild animals. Tell me a specific issue that could happen if two races integrated? I'm genuinely curious to hear what you are so afraid of happening.