A Dog's Purpose

This was sent to me via email and I'm not certain of the original source, but it could be from one of the Chicken Soup books.  If you know, please email to let us know.
A Dog's Purpose (from a 6-year-old)

Being a veterinarian, I had been called to examine a
ten-year-old Irish Wolfhound named Belker. The dog's owners,
Ron, his wife Lisa, and their little boy Shane, were all
very attached to Belker, and they were hoping for a miracle.
I examined Belker and found he was dying of cancer. I told
the family we couldn't do anything for Belker, and offered
to perform the euthanasia procedure for the old dog in their
As we made arrangements, Ron and Lisa told me they thought
it would be good for six-year-old Shane to observe the
procedure. They felt as though Shane might learn something
from the experience.
The next day, I felt the familiar catch in my throat as
Belker's family surrounded him. Shane seemed so calm,
petting the old dog for the last time, that I wondered if he
understood what was going on. Within a few minutes, Belker
slipped peacefully away.
The little boy seemed to accept Belker's transition without
any difficulty or confusion. We sat together for a while
after Belker's Death, wondering aloud about the sad fact
that animal lives are Shorter than human lives.  Shane, who
had been listening quietly, piped up, 'I know why.'
Startled, we all turned to him. What came out of his mouth
next stunned me.
I'd never heard a more comforting explanation.
He said, 'People are born so that they can learn how to
live a good life - like loving everybody all the time and
being nice, right?' The six-year-old continued, 'Well, dogs
already know how to do that, so they don't have to stay as