“Growth is life, and life is for ever destined to make for light.”
The narrator uses the wolf cub’s urge to leave the cave as a metaphorically charged picture of growth pushing living things toward wider experience despite fear and restraint.
Source details
White Fang, Part II, Chapter IV, ‘The Wall of the World,’ Project Gutenberg #910. The narrator says ‘Growth is life, and life is for ever destined to make for light’ as the grey cub disobeys fear and moves toward the cave opening. It remains literary animal-development narration and metaphor rather than a modern biological, developmental or behavioral law.