The baubellum is more developmentally and evolutionarily labile than the baculum.

Area of Science:

• Evolutionary biology
• Comparative anatomy
• Mammalogy

Background:

• Sexual dimorphism, the distinct differences between sexes, is a key area in evolutionary biology.
• The baculum (penis bone) is common in mammals, with a homologous structure, the baubellum, found in the female clitoris.
• Understanding the evolutionary relationship between these homologous structures can shed light on sexual dimorphism.

Purpose of the Study:

• To investigate the evolutionary correlation and developmental patterns of the baculum and baubellum across mammalian species.
• To determine if the presence and evolution of the baculum and baubellum are linked.
• To assess the functional significance of the baubellum in relation to the baculum.

Main Methods:

• Phylogenetic analysis of baculum and baubellum presence/absence across 163 mammalian species.
• Comparative scoring of bone presence across diverse mammal clades.
• Analysis of ontogenetic variability and morphological variation within species.

Main Results:

• A strong correlation exists between baculum and baubellum presence/absence in most species (134/163).
• The baubellum exhibits significantly more evolutionary transitions and recent losses compared to the baculum (29/163 species have a baculum but no baubellum).
• The baubellum displays greater ontogenetic variability and morphological diversity than the baculum, even when both are present.

Conclusions:

• The baculum and baubellum are generally evolutionarily linked in mammals.
• The baubellum is more evolutionarily labile and developmentally variable than the baculum.
• Increased evolutionary transitions and developmental noise suggest the baubellum may be nonfunctional and prone to loss.