On the first day God created the cow. God said, "You will go into the field
with the farmer and suffer under the hot sun, have calves and give milk
to support the farmer and for this I will give you a life span of sixty
years."
The cow said, "That's sort of a tough life you want me to live for
sixty years. Let me have twenty years and you can have the other forty back."
God agreed.
On the second day, God created the dog. God said, "You'll sit all day by the door of your house and bark at anyone who comes in or walks past. I'll
give you a life span of twenty years."
The dog thought then said, "That's too long to be barking. Give me ten years
and I'll give back the other ten."
So God agreed.
On the third day God created the monkey. God said, "You'll entertain people, do monkey tricks, and make everyone laugh. I'll give you a life span
of twenty years."
The monkey said, "How boring, monkey tricks for twenty years? I don't think
so. The Dog gave you back ten, so that's what I'll do also, okay?"
And God agreed again.
On the fourth day God created man. God said, "You'll eat, sleep, play, have sex, and enjoy life. Your life span will be twenty years." Man thought and said, "What? Only twenty years? No way. Tell you what, I'll take my twenty, plus the forty the cow returned, and the ten the dog gave back and the ten the monkey gave back. That totals eighty years, okay?"
"Okay," said God, "You've got a deal."
So that's why for the first twenty years we eat, sleep, play, have sex, and enjoy life; for the next forty years we slave in the hot sun to support our family; for the next ten years we do monkey tricks to entertain our grandchildren; and for the last ten years we sit in front of the house and bark at everybody.