If we made contact with an alien species which was clearly intelligent/sentient, but at a very different level to us, for example, if in the future humans found a planet inhabited by a species which was approximately as intelligent as our distant ancestors (and ancestors which were less intelligent than us for genetic, not simply environmental reasons), should we consider one alien to be as important as one person?
Whatever conclusion I come to seems to throw up problems: if we say yes, then should we consider the life of a chimpanzee to be as important as that of a human? If we say no, then presumably we would have to concede that if we met aliens more intelligent than us then we would be less important than them. Or perhaps there's a base level of intelligence above which all sentient beings are equal, but how would we determine that base level? On the other hand, if we move away from intelligence and look for something else like signs of a capacity for love or mourning to evaluate a species moral worth, this implies we might have to start to consider animals like dogs or elephants, which seem to show some of these, morally equal to humans.
I know the question of whose life is 'more important' is probably an odd one, and even sounds pretty unpleasant, but we could conceive of a situation where it came up. For example, imagine a twist of the trolley question where you have to decide whether or not to change the direction of a runaway tram and either let two people die, or actively kill one person. Well, what if the question was let a human die or kill a less intelligent (but sentient) alien? (Presumably if it was a chimpanzee or a dog most people would kill the animal rather than let the person die.) And of course, there are many other questions it would lead to such as what if we wanted to colonize the planet, and in a way which avoided slaughtering the aliens or badly damaging the environment of the planet, but they clearly didn't want us to? Should we worry about their wishes if we feel they are being irrational?
Sorry if I've been a bit long winded, and I know this is all very hypothetical and a bit scifi, but I think it's an interesting question and I hope I'm not the only one!