Because it didn't evolve in any other species. That wasn't very helpful. More to the point, it may not even be true. For all we can say for sure, other hominid species (perhaps Neanderthal?) had language, but didn't survive. In any case, the question of just why a particular trait did or didn't show up more than once in evolutionary history may not have any clear or uniform answer. The philosophical issue here, I suppose, might be whether the fact (if it is one) that as useful a trait as language only appeared in one species makes some sort of difficulty for the theory of evolution. Someone might claim: if the evolutionary picture really is correct, we would expect to see many species with this trait. Being neither a biologist nor a philosopher of biology, I can't say for sure. But I'm strongly inclined to suspect that this just isn't a good reading of evolutionary theory. Given the complexity of language-capable brains, what might be surprising is that the ability appeared even once. But it...

It's hard to give an all-purpose answer. But notice: the way you've posed the problem suggests that if cloning does more harm than good, it would be morally acceptable. People who think right and wrong are a matter of consequences would agree; people with a different way of thinking about right and wrong might not. Someone might argue, for instance, that trying to make copies of people shows a fundamental lack of respect for the humanity of the beings who result -- doesn't treat them as "ends in themselves." I'm not sure that would be a convincing argument, but it's easy to imagine it being made. As to whether cloning people might have net benefits, the answer surely is that it would depend on a lot of other things, which is one reason why it's hard to give a blanket answer to your question.

It may well be that there's an evolutionary story to be told about how we come to adopt moral codes and so on. But your question, as I'm reading it, is whether this undermines the objectivity of morality -- leads to the conclusion that our moral views are neither correct nor incorrect, or something like that. In fact, the two issues seem quite distinct. Compare: No doubt our ability to sort things by shape evolved and helps us survive. But that doesn't mean things don't really have shapes, nor that our beliefs about shapes are somehow flawed or empty or merely a "refined survival technique." There's a third strand to be separated out here. If there is such a thing as objective morality, what makes it objective isn't the fact that it's to be found in some scripture or other. On the one hand, none of us needs scripture to be convinced that wanton cruelty is wrong. And on the other hand, some things called for in some scriptures don't seem right on reflection at all. To sum up, what evolution...

We do have a lot in common psychologically, and all of that matters when we're trying to decide what's right and wrong. And the more we know about the psychological effects of how we treat people, the more information we'll have to feed into our ethical decisions. Psychologists have relevant things to say, as do doctors and, for that matter, economists, massage therapists, and various other specialists. Whether or not knowing everything about what makes people happy would settle all ethical questions, however, is another matter. (Not sure if you were suggesting it would.) For example: suppose that there are things that would make me happy at your expense. Most of us don't think it's just a matter of comparing the sum of my potential pleasure to the sum of your potential pain. Questions about fairness, for example, will also matter, and psychologists have no special expertise in sorting out what's fair. (Neither do most philosophers, for that matter.) There's also room to argue about...