Most Writers Are Human, and humans are mammals. Despite less than 1% of animal species being mammal (thus able to birth live), some writers, especially when writing an anthropomorphic animal work, may find a non-mammal laying and rearing eggs odd and have them reproduce the mammal way.

This trope also applies to monotremes, that special order of mammals which lay eggs, living creatures that reproduce by splitting up, mythological creatures that are not usually depicted as giving live birth, and even an