You see, when we first started travelling between the stars, seeking out strange new lifeforms, settling other planets, we realized that we really missed our fuzzy little companions. Unfortunately, cats were not cut out for space travel. They couldn't cope with microgravity, and they had a distressing tendency to eat random stuff off the floor. Because that random stuff often was of alien origin, with a vastly different biochemistry, the cats usually got violently sick and died soon after.
This made us very sad. So we decided to use our considerable knowledge of biology and genetics to fix this problem. After decades of research and experimentation, we created NeoCats.
NeoCats look and feel and behave identically to old-style domestic cats, but they're actually less related to them than squid. They're capable of dealing with a huge range of poisons, alien proteins and extraterrestrial fungi. They love microgravity. They can regenerate lost limbs with ease. They can subsist on pretty much anything that's vaguely organic in nature. Plastic bags? Nutritious! Methane-breathing alien life? Delicious!
So we cloned a whole bunch of NeoCats in a variety of beautiful pelt colours and took them with us on our adventures, and kept them as pets on our colonies. Of course, eventually, some of them... wandered off. And found other NeoCats, out there, and had cute NeoKittens, who in turn found their way onto all kinds of spacecraft, human and alien.
The galactic community at large first noticed that there might be a serious problem when they lost contact with the G'7zk, a rather solitary species inhabiting a single, remote planet. An expedition was despatched, and they found the G'7zk vanished. They also found a large number of NeoCats, who seemed extremely pleased to see them.