Therefore, discovery of the female penis itself is not truly a novel discovery for the study. The novel discovery presented in Yoshizawa et al. (2014) is that the female Neotrogla can coercively grasp and copulate with a male for a long time by using the penis. In animals, coercive mating is generally an exclusive feature of males (Arnqvist & Rowe 2005), and it means that there is less chance to perform pre-copulatory female choice. Instead, females sometimes discard sperm from low-quality males or seek re-mating with a superior male (post-copulatory or cryptic female choice: Eberhard 1996). However, these options are not available for male Neotrogla because males do not receive gametes from females. How do males respond to coercive mating by females? This is a unique question about sexual selection, to which only Neotrogla can answer. It is also important to unveil why, among many sex-role reversed animals (i.e., the animals in which males invest more for offspring than females via nuptial gift or paternal care: Gwynne 2008), only Neotrogla evolved the elaborated female penis. To understand this, we have to study the behavioral (such as mating posture), physiological (such as the characteristics of the spermatophore: the capsule containing semen and nutrition), and developmental (such as the developmental origin of the gynosome) backgrounds (or pre-adaptations) that enabled Neotroglato originate the female penis.