Fukigen na Jiin plot
Yoshiko Aoi is a researcher in ethology, the study of animal behavior, at a Japanese university. Through her studies, Yoshiko learns that the man's genes cause men to be born unfaithful. This is the sad but widely accepted theory of biology. What's even sadder is that Yoshiko's nickname is 'Gene', because her name, written in Chinese characters, can also be read as 'Jinko/Geneko'.