[ShadowAce]

You are not seriously trying to suggest that this is some kind of unsolved mystery, are you?

Tell you what--you find a creature that asexually reproduces into a sexually-reproducing creature and get back to me.

Until then, it's all just theory--and not the scientific kind.

[grey_whiskers]

The humor columnist Dave Barry wrote back in 1996 about

...a tiny creature called Symbion pandora (literally, "a couple of Greek words"). The zoology community, which does not get out a lot, is extremely excited about Symbion pandora, because it reproduces differently from all other life forms. According to various articles, when Symbion pandora is ready to have a baby, its digestive system "collapses and is reconstituted into a larva," which the parent then gives birth to by "extruding" it from its "posterior." In other words-correct me if I am wrong here-this thing basically reproduces by pooping.

source.

Not quite the same thing, but still funny enough to post.

Cheers!

[Muridae]

Meaning no disrespect, even a cursory browsing reveals an example that fits your description: mating in S. cerevisiae, or baker’s yeast.

http://en.wikipedia.org/wiki/Yeast_mating

Sexual reproduction and the diploid genome are related, and have quite a bit of research backing the evolutionary model.