Lines 36–40: What details from these lines convey the naturalistic view of life as a harsh struggle for survival?

temperature, and upon man’s frailty in general, able only to live within certain narrow limits of heat and cold, and from there on it did not lead him to the conjectural[3] field of immortality and man’s place in the universe. Fifty degrees below zero stood for a bite of frost that hurt and that must be guarded against by the use of mittens, earflaps, warm moccasins, and thick socks. Fifty degrees below zero was to him just