And you thought you knew everything...

1 Life emerged on earth about 3.8 billion years ago, but sex did not evolve until more than 2 billion years later. Dirty limericks emerged only quite recently, geologically speaking.

2 Sex—what is it good for? Scientists are not sure, since asexual reproduction is a better evolutionary strategy in some important ways.

3 For those who refuse to commit to one strategy: The hermaphroditic earthworm Dendrobaena rubida has both male and female genitalia. If it cannot find a partner, the worm doubles up so that its female bits and male bits can go to town.

4 Although famously monogamous, female Adélie penguins slip away from their mates occasionally to couple with unattached males. They exact a fee (pdf) for such a dalliance—stones to bolster their nests—not unlike certain people.

5 Some talented penguin teasers can get a gift even without putting out. Again, not unlike certain people.