“They will change,” read Alex, “after a catastrophic event, radically altering their bodies, culture, social bonds. Every tribe member will participate in the social change; however, only the young adults and children will change physically to meet their new environment, the chameleonic ability being lost at the end of estrus. Though the old do not change — and thus may seem to be members of an entirely different species — they are not cast off by the tribe, nor relegated to subsidiary social positions. They are the new keepers of the past, of the long genetic history of the tribe. For when the tribe changes, when the old bodies are sloughed away, the old heads remain, vestigially; two of these, a male and a female, are collected by the oldest surviving tribe member. They feel that, so long as the heads are kept, the tribe cannot die.”

Alex closed the book, put it on top of the refrigerator. Inside two shriveled hominid faces stared back at him patiently. “Huh,” he said.