This paper is on Butler’s Clay’s Ark, constitutes the beginning of a history played out in the earlier volumes. A man returns to earth from a distant galaxy, inadvertently carrying a disease organism that begins the transformation of the human race. The organisms invade and recode human DNA. Threatening the lives of their hosts if they are not transmitted to other humans. Because transmission requires the breaking of the skin of the uninfected person, the organisms trigger violent behavior and overwhelming lust. The children of the inevitable sexual couplings between infected individuals are not human; they look like catlike, graceful animals and mature rapidly into highly intelligent quadrupeds with superhuman senses of smell and hearing. Resistance to the organism’s need to spread, which is impossible except in the case of isolated individuals, ensures physical and mental anguish culminating in death. Clay’s Ark the least utopian of the patternist book presents three recently infected individuals attempting to maintain their humanity, which in this context signifies their control over biological drives. Key words: organism, transmission, biological, overwhelming