The biggest way in which this novel presents key truths about the nature of humanity is through the transformation that occurs within Jim from the pampered, somewhat spoilt boy that the reader is presented with at the beginning of the novel to the war-weary, prison camp and street-smart teenager that is able to survive in the face of tremendous opposition. Jim faces tremendous hardship, and starves and sees sights that leave an indelible impact on his psychology. As a result of these experiences, he changes irrevocably, and learns certain truths about the nature of humanity and man's inherent fragility in the face of death, war and suffering. Note how this is conveyed in the following quote that comes towards the end of the novel after Jim's quest for his parents is nearly over:
To his surprise he felt a moment of regret, of sadness that his quest for his mother and father would soon be over. As long as he searched for them he was prepared to be hungry and ill, but now that the search had ended he felt saddened by the memory of all he had been through, and of how much he had changed. He was closer now to the ruined battlefields and this fly-infested truck, to the nine sweet potatoes in the sack below the driver's seat, even in a sense to the detention center, than he would ever be again to his house in Amherst Avenue.
Now that he is abot to reunited with them, he is struck by the horror of all he has endured and becomes suddenly aware of how far he has travelled and how much he has matured. The pampered, sheltered upbringing he experienced in Amherst Avenue belongs now to another world, and he is more defined by the "ruined battlefields" and the carnage of war with all of its want and suffering than he ever was by the luxury and comfort he once enjoyed. The nature of humanity is thus expressed in its fragility through the carnage of war and how it irrevocably changes Jim.