Though but ten years old he was fully as strong as the average man of thirty, and far more agile than the most practiced athlete ever becomes. And day by day his strength was increasing.
His life among these fierce apes had been happy; for his recollection held no other life, nor did he know that there existed within the universe aught else than his little forest and the wild jungle animals with which he was familiar.
He was nearly ten before he commenced to realize that a great difference existed between himself and his fellows. His little body, burned brown by exposure, suddenly caused him feelings of intense shame, for he realized that it was entirely hairless, like some low snake, or other reptile.

Ch. 5 : The White Ape - Tarzan of the Apes (1912)