The Hebrew Bible's notion of humanity "created in the image of God" (Genesis 1:27) has loomed large in discussions of Christian and Jewish conceptions of humanness. The contemporary entailments of such discussions range across the domains of law, ethics, and politics. This talk provides an alternate angle onto the makings of humanness found in classical Jewish sources. It argues that the rabbis of late antiquity understood the limits and makings of the human within larger considerations about reproduction, the classification of species, and the problem of species hybridity. The talk shows how, at the intersection of menstrual and purity law, agricultural law, and temple-related rules, the early rabbis effectively mapped a "biology" that sought to determine the boundaries and the overlaps between species.