[j. d. worthington]

It's seldom the main focus, I think, but a lot of them touch on it. Heinlein frequently makes references to this sort of thing, and Leiber does on occasion (The Wanderer, for instance); Asimov has done some, as well (in fact, when he was getting his degree in biochemistry, he refused to attend on the day they were doing dissection of a cat, if I remember correctly).

Also, one needs to remember that a lot of the "sentient species" aspect of sf is also a metaphor for both humans of other cultures and for our treatment of other species, our arrogance concerning their intellect, for example... this is quite clear, for instance, in Heinlein's juveniles such as Space Cadet, Between Planets, and Red Planet (among others).