In all his travels nothing that Darwin beheld made a deeper impression on his sensitive mind than primitive man. "Of individual objects, perhaps nothing is more certain to create astonishment than the first sight in his native haunt of a barbarian--of man in his lowest and most savage state. One's mind hurries back over past centuries, and then asks, could our progenitors have been men like these?... I do not believe it is possible to describe or paint the difference between savage and civilized man." It was at Tierra del Fuego that he was particularly shocked. He admired the Tahitians; he pitied the natives of Tasmania, corralled like wild animals and forced to migrate; he thought the black aborigines of Australia had been underestimated and remarked with regret that their numbers were decreasing through their association with civilized man, the introduction of spirits, the increased difficulty of procuring food, and contact with European diseases. In this last cause tending to bring about extinction there was a mysterious element. In Chile his scientific acumen had been baffled in the attempt to explain the invasion of the strange and dreadful disease hydrophobia. In Australia the problem of the transmission to the natives of various diseases, even by Europeans in apparent health, confronted his intelligence. "The varieties of man seem to act on each other in the same way as different specimens of animals--the stronger always extirpating the weaker." It was at Wollaston Island, near Cape Horn, however, that Darwin saw savage men held in extremity by the hard conditions of life, and at bay. They had neither food, nor shelter, nor clothing. They stood absolutely naked as the sleet fell on them and melted. At night, "naked and scarcely protected from the wind and rain of this tempestuous climate," they slept on the wet ground coiled up like animals. They subsisted on shell fish, putrid whale's blubber, or a few tasteless berries and fungi. At war, the different tribes are cannibals. Darwin writes, "It is certainly true, that when pressed in winter by hunger, they kill and devour their old women before they kill their dogs." A native boy, when asked by a traveler why they do this, had answered, "Doggies catch otters, old women no." In such hard conditions what are the characteristics that would determine the survival of individual or tribe? One might be tempted to lay almost exclusive emphasis on physical strength, but Darwin was too wise ultimately to answer thus the question that for six or seven years was forming in his accurate and discriminating mind.