>>From an evolutionary point of view, asexual reproduction (cloning oneself) is a lot less costly than sexual reproduction

Yes, there's a cost, but it's worth considering what evolutionary pressures led to sexual reproduction. Personally, I suspect it has to do with microbes having much shorter generational times, letting them essentially evolve 'keys' to our immunological 'locks' - and the genetic diversity that comes out of sexual reproduction changes the combination to the 'lock'.

Yeah, I realize that for every evolutionary puzzle, there's an answer that's simple, elegant - and wrong. But that doesn't change the fact that there had to be some kind of evolutionary pressure.