Dante was born as part of an experimental program tinkering with artificial hybridization in order to achieve "improved" soldiers and other such "utility" roles.  He is one of the few "true-born" hybrids, born from a surrogate who was implanted by a human egg fertilized by modified alien genetics code.  He's also considered slightly faulty, as the genes selected in the hopes of making him extra-fast and nimble actually have made him quite fragile, and he can only run in very short bursts before his joints become too inflamed.  Luckily he compensates by having incredible eyesight and has become a crack shot, as a result.

Mara was raised in the program alongside Dante, under the impression that she was a "tank-baby" with no "real" parentage to speak of.  She does not know the specifics of her genetics, or the truth of how her human father was murdered in order to kidnap her away from where she was born, with her Yautja mother.  While she looks MOSTLY-human, she is still growing even at the age of 20, at the time of her storyline and will eventually top out at just shy of 7 feet.  Her bones and muscles are denser and stronger than a human's, and she has sharpened teeth and nails.  She is slightly ostracized by others in the program due to her apparent lack of "downsides" and the fact that their overseeing commander clearly favors her, but from an early age they learn not to fuck with her.