Many studies of mermaids in literature discuss femininity, otherness, and the impossibility of communication between merfolk and human beings. They operate on the assumption that merfolk are mainly mermaids, although there are examples of mermen in many European legends, European literature, and natural history.
In this paper, I discuss the transition of merfolk in natural history. In the ancient times, witnesses' accounts of the males Triton and Nereus were introduced. In the Medieval Bestiary, female Sirens were pagan others who seduced men. During the Renaissance, naturalists depicted merfolk with anatomical descriptions and detailed views based on reports of merfolk “mummies" and “bones" from all over the world. People regarded manatees as merfolk and classified both as fish.
Carl von Linné created the concept of Mammalia, reclassified manatees into this new group, and removed Sirens from his Systema Naturae. Naturalists in the 18th century thus denied the existence of merfolk. In The Animal Kingdom, George Cuvier wrote that people mistook manatees for mermaids because they have two breasts and feed their young with their own milk. Behind this idea is the modern view of women and family: breastfeeding is the role of the mother, not a wet nurse. Breastfeeding shows the “ideal" maternal instinct or bestiality in female manatees, mermaids, and women, who have the same upper bodies as mermaids. Through its representation of mermaids, natural history underlined the commonality of manatees as beasts and human females and gave the “scientific" endorsement of mermaids' otherness, inability to communicate verbally, and “femininity."