Once Upon A Time

in a land totally unlike our own:

It seemed like an ordinary day in the primordial ooze, but romance was in the methane-ammonia air. An amoeba, pseudopoding along as usual, met and was enchanted by a particularly lovely photosynthetic bacterium. He took her inside his cell membrane, but instead of digesting her as he first planned, the two fused into a single organism. The bacterium gave the amoeba the new ability to absorb energy from sunlight, and their descendants became every plant in the world.

Kind of sweet, really.