Biological Realities of Life

The main theme of the book is about life and death. Throughout the book, you see Jody having to deal with the painful and slow death of his best friend, Gabilan. Then he is promised a new pony colt but that comes with the price of Nellie having to die.
"'Jody,' he explained, 'the buzzard didn't kill the pony. Don't you know that?' '1 know it,' Jody said wearily.'"