Sexes are polymorphisms: Describing and understanding sexual diversity as phenotypic variation

Area of Science:

• Evolutionary Biology
• Developmental Biology
• Genetics

Background:

• Current frameworks for describing biological sex lack precision.
• Sex is often treated as a distinct category rather than a form of variation.
• Understanding phenotypic variation is crucial for evolutionary and developmental studies.

Purpose of the Study:

• To propose phenotypic polymorphism as a unifying framework for studying biological sexes.
• To demonstrate that mechanisms producing sexes are identical to those producing other polymorphisms.
• To highlight how this framework can capture the diversity of reproductive strategies.

Main Methods:

• Comparative analysis of reproductive strategies across diverse taxa.
• Examination of genetic, developmental, and evolutionary principles underlying polymorphism.
• Literature review on phenotypic variation and its role in reproduction.

Main Results:

• Sexes are a type of phenotypic polymorphism, sharing underlying mechanisms with other polymorphisms.
• No fundamental genetic, developmental, or evolutionary principle distinguishes sexes from other polymorphisms.
• Polymorphisms can play a central role in reproduction, similar to sexes.

Conclusions:

• Treating sexes as phenotypic variation offers a more descriptive and empirical understanding of reproductive types.
• The polymorphism perspective clarifies that sexes are a population-level trait.
• Existing analytical tools for variation can be applied to study reproductive types and their evolution.