If you were the last person in the world.

I just finished reading Z for Zachariah by Robert C. O'Brien. It's a post-apocalyptic novel about a 16 year old girl and a 30 year old man who are the only known survivors of a nuclear war.

They meet each other after a year, and about halfway through, the book gets all creepy because the man tries to rape her. The story moves from man vs. nature to man vs. man.

I thought that was such an odd thing for a character in that situation to do. I think if the last two people in the world are roughly reproductive age, they're naturally just going to have sex eventually anyway.

It's human nature. Look at Adam and Eve. They obviously figured out what needed to happen. Even if they don't like each other much, what other choice did they have?

Then again the book wouldn't be as exciting if the characters just naturally had sex.

Tiger Woods had 7 or 8 affairs while married.

Now that it's come to light Tiger Woods was cheating on his wife, I ask people if they're surprised. I get mainly two responses:

1) "Yes! I'm very disappointed. How could he do that to his wife? He's going to lose his sponsors."

2) "No big deal. He's a normal billionaire. They all cheat on their wives."

On the one hand, Tiger made a promise to be faithful to his wife. Breaking this promise, hurting his family and jeopardizing his career seems spectacularly dumb.

On the other hand, Tiger is a male human being whose genes have programmed him to want sex with as many beautiful women as possible. Even if his willpower is 99% - and surely as a professional athlete he's been propositioned over 100 times - the one time he makes a mistake brands him forever as a "cheater". (Of course he made 7 or 8 mistakes.)

Doesn't sound fair.

This situation brings up the fascinating question: is monogamy a natural state between two human beings? I don't know.

What I do know is that many male rodents deposit a plug of mucus inside the female's reproductive tract after they ejaculate. The mucus plug stops other male sperm from going into the female's vagina.

But the rat penis has a little suction cup at the tip. It sucks out the plug like a toilet plunger. Some females reach inside their vagina and pull out the plug with their claws. Then they eat the plug.