> Some birds, whales, elephants are near the top. They're different from humans, but much closer than we expect: mammals (apart from the birds, sure), with sim

> Some birds, whales, elephants are near the top. They're different from humans, but much closer than we expect: mammals (apart from the birds, sure), with similar skeletal structure, similar overall "how it works" biology (brains, skeleton, digestive system, circulatory system, etc) The closest "intelligent alien" we know of is the octopus. That's really something else. But even then a lot of biology is shared. If you want to get creative don't think of humans mating neanderthals, think animals re-evolving from an earthworm or a jellyfish.