[Mikumo's not technically human, but that's also about the last thing she's going to correct anyone on, so she rolls with it. The question gets a bit of a one-sided shrug, even if she feels like there has to have been some kind of examination done as far as selecting them went.]

I would guess they needed to study us somehow to decide that we were compatible, though how they did it is still an open question. [It ties back into how advanced the technology used must have been to draw them to here from so many corners of the galaxy, and from across different dimensions.] It could be a numbers game, as far as human preference. Humans are definitely one of the most prolific species in the galaxy where I come from.