In Life of Pi, how does the use of symbolism and allegory give the readers a better understanding of Pi's descent into savagery?

It seems that the answer to this question is linked with
the "alternative" version of events that Pi gives to Mr. Chiba and Mr. Okamoto in
Chapter 99 of the tale, who are obviously unconvinced by the version that Pi gives them
and us as readers. Trying to come up with a different story, Pi gives a much more
realistic account of what supposedly happened, with each of the animals clearly
represented by a character. Thus it is that the zebra is replaced by a sailor, the hyena
by the cook, and the orangutang by his mother. Interestingly, the only animal that is
absent is Richard Parker, the tiger, which suggests that allegorically Richard Parker in
the "first" tale represents Pi himself. The second tale charts the way in which Pi was
forced to kill the Cook and how he ate human flesh to sustain
himself:

I
stabbed him in the throat, next to the Adam's apple. He dropped like a stone. And died.
He didn't say anything. He had no last words. He only coughed up blood. A knife has a
horrible dynamic power; once in motion, it's hard to stop. I stabbed him repeatedly. His
blood soothed my chapped hands. His heart was a struggle--all those tubes that connected
it. I managed to get it out. it tasted delicious, far better than turtle. I ate his
liver. I cut off great pieces of his
flesh.

Note how Pi is forced
to become savage himself to survive. He later comments that the sailor was an evil man,
but that worse was the way in which he met "evil" in Pi too. By allegorically creating
Richard Parker to represent this untamed savagery in his original story, Pi symbolically
indicates his own descent into savagery in his grim battle for
survival.