Does greater variation reside in the larger sex?

Area of Science:

• Evolutionary Biology
• Zoology
• Comparative Anatomy

Background:

• The question of which sex, male or female, exhibits greater variability has been a long-standing debate in biology.
• Previous assumptions often favored greater male variability, potentially due to a focus on species with intense male-male competition.

Purpose of the Study:

• To investigate the relationship between body mass and sexual variation across a diverse range of mammalian species.
• To determine if body size or sex is the primary driver of within-sex variability.

Main Methods:

• A phylogenetically informed analysis was conducted on the body mass of 337 mammalian species from six orders.
• Regressions were used to analyze the relationship between male:female mass variance and male:female mean mass.

Main Results:

• In most mammalian orders studied, the larger sex (male or female) exhibited greater body mass variation.
• The variation-size relationship was often close to unity, suggesting size as a primary driver of variability.
• Deviations were observed in Chiroptera (bats) and Rodentia (rodents), indicating additional factors influencing sexual dimorphism in variability.

Conclusions:

• Body size, rather than sex per se, appears to be the main determinant of within-sex variability in many mammalian species.
• While size is a key factor, sex-specific influences on variability may exist in certain groups, such as bats and primates.
• The historical focus on species with pronounced sexual dimorphism may have skewed previous understandings of sexual variation.