This says it all!

On the first day, God created the dog and said:

'Sit all day by the door of your house and bark at anyone who comes in or
walks past. For this, I will give you a life span of twenty years.'

The dog said: 'That's a long time to be barking. How about only ten years
and I'll give you back the other ten?'

So God agreed.
On the second day, God created the monkey and said:

'Entertain people, do tricks, and make them laugh. For this, I'll give you a
twenty-year life span.'

The monkey said: 'Monkey tricks for twenty years? That's a pretty long time
to perform. How about I give you back ten like the Dog did?'

And God agreed.
On the third day, God created the cow and said:

'You must go into the field with the farmer all day long and suffer under
the sun, have calves and give milk to support the farmer's family. For this,
I will give you a life span of sixty years.'

The cow said: 'That's kind of a tough life you want me to live for sixty
years. How about twenty and I'll give back the other forty?'

And God agreed again.
On the fourth day, God created man and said:

'Eat, sleep, play, marry and enjoy your life. For this, I'll give you twenty
years.'

But man said: 'Only twenty years? Could you possibly give me my twenty, the
forty the cow gave back, the ten the monkey gave back, and the ten
the dog gave back; that makes eighty, okay?'

'Okay,' said God, 'You asked for it.'
So that is why for our first twenty years we eat, sleep, play and enjoy
ourselves. For the next forty years we slave in the sun to support our
family. For the next ten years we do monkey tricks to entertain the
grandchildren. And for the last ten years we sit on the front porch and bark
at everyone.

Life has now been explained to you.