Humans where made some-how. We dont know why and how they where made, but they all have an instinct to make new humans. The logical reson is because they all have mortality and want to last longer. Humans have a base instinct to live longer because of humans instinct to explore (E.G. the only reson we dont kill ourselfs is because we feel we must see more things). Human sex is a base part of the animal nature that Christian society has made sinful. So it is not in anyway sinful or shamful (all partys agreeing).
Not true, bonobo chimps are normally bisexual and have sex for social reasons other to produce offspring. I'm thinking the programme that said social reasons also meant pleasure as well.
But otherwise don't get too fond of dolphin speech, it isn't very complicated. Each click means something, regarding of where it is in speech, meaning only a few posiblilities in sentences are possible. Humans however use a bit more sounds BUT use them in a particular order to convey meaning (otherwise cat and tac would mean the same thing, and would probably be three words).