One.

If we didn't have birthdays, you wouldn't be you.
If you'd never been born, well then what would you do?
If you'd never been born, well then what would you be?
You might be a fish! Or a toad in a tree!
You might be a doorknob! Or three baked potatoes!
You might be a bag full of hard green tomatoes!
Or worse than than all that...Why you might be a WASN'T.
A Wasn't has no fun at all. No, he doesn't.
A Wasn't just isn't. He just isn't present.
But you.. You are YOU! And now isn't that pleasant!

~Dr. Seuss; Happy Birthday to You!