The excerpt shows the wilderness it is dog eat dog world and the only the strongest will survive. This is even explicitly said in the sentence:
<span>The
blood-longing became stronger than ever before. He was a killer, a
thing that preyed, living on the things that lived, unaided, alone, by
virtue of his own strength and prowess, surviving triumphantly in a
hostile environment where only the strong survived. </span> <span></span>The wilderness does not care and it is a hostile environment and if you want to survive you have to strong. <span />
The theme would be supported by these lines:The blood-longing became stronger than ever before. He was a killer, a thing that preyed, living on the things that lived, unaided, alone, by virtue of his own strength and prowess, surviving triumphantly in a hostile environment where only the strong survived. So I think the answer to your question would be the theme that illustrates this is that Only the strong survive in the wilderness.
