In the Beginning, God created the mule, and told him: "You will be a Mule, working constantly from dusk to dawn, carrying heavy loads on your back. You will eat grass but you will lack intelligence. You will live for 40 years."
The mule answered: "To live like this for 40 years is too much. Please, give me no more than 20." And it was so.
Then God created the dog, and told him: "You will hold vigilance over the dwellings of Man, to whom you will be his greatest companion. You will eat his table scraps and live for 25 years."
The dog responded: "Lord, to live 25 years as a dog is too much. Please, no more than 10 years." And it was so.
God then created the monkey, and told him: "You are a Monkey. You will swing from tree to tree, acting like an idiot. You will be funny, and you shall live for 20 years."
The monkey responded: "Lord, to live 20 years as the clown of the world is too much. Please, Lord, give me no more than 10 years." And it was so.
Finally, God created Man and told him: "You are Man, the only rational being that walks the earth. You will use your intelligence to have mastery over the creatures of the world. You will dominate the earth and live for 20 years."
The man responded: "Lord, to be Man for only 20 years is too little. Please, Lord, give me the 20 years the mule refused, the 15 years the dog refused, and the ten years the monkey rejected." And it was so.
And so God made Man to live 20 years as a man, to have mastery over the creatures of the world. Then he is to marry and live 20 years like a mule, working and carrying heavy loads on his back. Then he is to have children and live 15 years as a dog, guarding his house and eating the leftovers. Then, in his old age, he is to live 10 years as a monkey, acting like a fool to amuse his grandchildren. And it was so.