We generally think that humans have a dignity that non-human animals like dogs lack, even when the humans are so disabled that their functioning is on the level of a dog. While Kant rightly insists that dignity does not reduce to value, nonetheless dignity seems to imply a value. Perhaps the point generalizes so that it is better to be a member of a spiffier species even if one personally lacks those features that make the species spiffier.
This isn’t clear, however. I wish I had the amazing mathematical abilities of a Vulcan like Spock. I don’t really wish to be a mathematically disabled Vulcan, whose mathematical abilities are no greater than mine. And if the choice were between being a deficient Vulcan with mathematical abilities slightly weaker than mine and being what I am, I would prefer to be what I am, at least bracketing non-mathematical features of the two species. Thus whatever value there is in being a member of a species with much greater normal mathematical abilities seems easily outweighed by the value of actual mathematical abilities.
But now consider a somewhat different choice: that between being a human like me and a highly deficient Vulcan whose mathematical skills are nonetheless somewhat better than mine. Suppose, too, that in my chosen way of life only the mathematical skills would matter: nobody would make fun of me for having pointy ears, I wouldn’t feel sad at being a deficient Vulcan, etc. It seems quite reasonable to want to be such a deficient Vulcan. This suggests that either the small improvement in actual mathematical skills is ample compensation for being highly disabled, or being a Vulcan counts for a lot.
Being a Vulcan doesn’t seem to me to count for a lot. When I reflect why I’d rather be the deficient Vulcan with mathematical skills somewhat better than mine, neither the deficiency as such nor the Vulcanness as such count for much.
It seems of much greater value to be a deficient human than to be a normal dog, keeping actual abilities the same. But it doesn’t seem to be of much greater value to be a deficient Vulcan than a human, even if normal Vulcans were equal or superior to humans in all respects. Maybe this is because only a dignity-relevant difference between species makes a value difference between species, and Vulcans, even if they are superior, do not have greater dignity.
Or it could even be that the dignity difference doesn’t imply a value difference.