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...