Doona was a jewel of a planet -- a pastoral paradise with rivers, lakes, mountains & seas. The Hrrubans needed it to revitalise their decadent race, to give it back something of the old pioneering spirit. The Terrans needed it as an overspill from the hysterical crowding of Earth, a place to breathe & move without restrictions.
So they both sent a colonising party -- & they both began to think of Doona as Home. & then one day the smooth-skinned, two-legged mammal known as Man came face to face with the furry, four-pawed mammal known as Hrruban...