Aliens At Home

How often do two or more intelligent species originate on a single planet?  This happens in:

JRR Tolkien's Middle Earth

CS Lewis' Narnia (although the world of Narnia is not a planet)

Lewis' Malacandra (his version of Mars)

Poul Anderson's Jupiter in Three Worlds To Conquer

Anderson's Starkad in his Technic History

"'...their host is immense, and not even of our race. Two different breeds of thinking animal have met.'"

-Poul Anderson, Three Worlds To Conquer (London, 1966), 2, p. 19.

Those two land-dwelling species are of the same genus but there is also a rational species of another genus at a higher atmospheric level.

On Starkad, land and sea dwellers are natural enemies like men and wolves on Earth.

Malacandrians do not keep pets because, of the three species:

"Each of them is to the others both what a man is to us and what an animal is to us."

-CS Lewis, Out Of The Silent Planet IN Lewis, The Cosmic Trilogy (London, 1990), pp. 1-144 AT Postscript, p. 140.

Narnians include human beings, Talking Beasts, dwarfs etc. Lewis gets the same effect among his Martians.