Why human's life is longer than some of the domestic animal

God created the mule, and told him, "You are mule. You will
work constantly from dusk to dawn, carrying heavy loads on
your back. You will eat grass and lack intelligence. You will
live for 35 years."

The mule answered, "To live like this for 35 years is too
much. Please, give me no more than 20."

And it was so.

Then God created the dog, and told him, "You are dog. 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 30 years."

The dog responded, "Lord, to live 30 years as a dog like
that is too much. Please, no more than 10 years."

And it was so.

God then created the monkey, and told him, "You are monkey.
You shall 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 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 15 years the mule refused,
the 20 years the dog refused, and the 10 years the monkey
rejected."

And so God made Man to live 20 years as a man, then marry
and live 15 years like a mule working and carrying heavy
loads on his back. Then, he is to have children and live
20 years as a dog, guarding his house and
eating the leftovers after they empty the pantry;
then, in his old age, to live 10 years as a monkey, acting
like an idiot to amuse his grandchildren.

And it is so...