one day, a god: bob, was bored and asked his friend for some stuff. he picked a newspaper boy from his realm and a fucking gravemind (not originally from his realm but still) and merged them. a few new powers and not so hungry/greedy. then threw in the ark: a massive fuck off super weapon creator.

he also added some other creatures to the mix.
three races from the universe his friend calls Equis and clones of his ‘freinds’: the princesses and the elements of... uh, armory, no, harmony.
(also, the other planets are filled with life because his sons got bored.) four from his realm were chosen.
then he chucked the following species on the ark, these ones were chosen to go are the humans, the ponies, the Griffins, the Sangheili, the kig-yar, the flood, the creikt, and finally the changelings.

(The flood don’t count because they suddenly 'appeared' just like some of these guys traveled here and handed the humans the responsibility to create stuff. to which, he was proud to let them.)

even though their cousins: the forerunners, got jealous