Hypothesis: Compulsive hoarding as an atavism.

In this hypothesis paper, we propose that hoarding disorder may be an ancestral mammalian behavior, possibly hard-wired but dormant in present-day humans, that can be activated by traumatic experiences. To support this claim, we describe hoarding in ancestral mammals and provide examples of recurrence of traits, or atavisms, in humans and other mammals, highlighting its implications for neuropsychiatric diseases. We highlight the potential of using shrews as animal models for hoarding behavior and, considering the current knowledge on the molecular underpinnings of the disorder, we also point to limitations of the proposed connection.