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    While biologists argue about the limits and definition of a species, the urge to cluster and distinguish among the plenitude of lifeforms that populates the planet remains. Contemporary concerns about attempts to clone monkeys and to engineer human-porcine chimeras point to problems with species boundaries, resemblances, and causing suffering to other creatures. The fears about resemblances (and attendant slippery slope concerns) relate to how humans may be implicated. Such concerns about resemblances among kinds, the boundaries between species, and attempts to uphold distinctions, also populated late ancient zoological and anthropological thought, including that of the rabbis. While the rabbis drew somewhat on tselem elohim (humans as images of God) to theorize human reproduction and uniqueness, this article traces an alternative zoological vision that integrated humans among other kinds, while explaining resemblances among species with a theory of territorial doubles. This theory of territorial doubles claimed that all creatures—including humans—have versions that exist in the wild and in the sea. The article follows rabbinic zoological classifications as they sought to order lifeforms, viewed as similar and/or distinct.