"Selective--oh, yes! Survival of the fittest ... all that fiddle-di-diddle? You mean the present Titanians _are_ the present Titanians simply because they adapted their physiques to the surroundings, eh? Why, rather! That's clear enough. Still, if they can stand the radiation, I don't see why other humans--" "Other _humans_!" Grossman laughed curtly. "My dear Doctor, it is obvious you have never seen a Titanian. Human, indeed! Why, it is the dissimilarity between the Titanians and ourselves which led me to name racial divergence as among the hazards of life on Titan. "The creatures who rule Titan look less like humans than like those monsters deranged and alcoholic patients see in their dreams. For some reason--possibly because of this mysterious T-radiation--the denizens of the world have never bred true. Consequently, there is no way of foretelling what the child of any two parents may resemble ... though one almost certain guess is that it will resemble neither parent. "Bilateral symmetry is about the only constant human attribute to be found amongst the Titanians. That and a more or less rudimentary intelligence ... an instinct which is more akin to animal cunning than to intellect. "Some Titanians walk erect on their hind legs. Some crawl on all fours or squirm on their bellies. Some resemble the humanoid races of our planet, or Mars, or Venus. Others look like obscene jungle beasts, ghouls, fabulous monsters. "I have seen Titanians whose leprous flesh covered bones have no counterpart in the human skeleton ... others with no faces at all, as we know the meaning of the word ... others who grope blindly along on tactile tentacles, 'seeing' with foot-long tongues, 'hearing' through their fingertips. "Some there are who look like gigantic, crimson ants; others inch their way along the streets like hideous, mangled slugs; while yet again--astonishingly--you may chance upon a Titanian not only similar in appearance to Earthmen, but as clever and quick in thought as any terrestrial." Grossman paused, nodding significantly. "These," he said, "are the most dangerous of all." "And--" breathed Lynn Graham--"the nature of this danger, Mister Grossman? Attack, perhaps?" "Attack!" The trading-post factor laughed brusquely, harshly. "A mild word for it. Extermination! The Titanians hate interlopers on their world--_particularly_ Earthmen--with a smoldering, implacable hatred inconceivable to a civilized mind. Had they their will, they would hunt down every Earthman and slaughter him with the most horrible tortures their warped and twisted minds can devise.