Homology and ontogeny: pattern and process in comparative developmental biology

Area of Science:

• Evolutionary Biology
• Developmental Biology
• Comparative Morphology

Background:

• Homology is traditionally assessed using similarity and developmental patterns.
• Existing definitions of homology often conflate developmental stages and processes.
• The role of topology in homology assessment is debated due to positional ambiguity.

Purpose of the Study:

• To critically evaluate the relationship between development and homology.
• To propose a refined definition of homology based on complexity.
• To distinguish between homologizing developmental stages and processes.

Main Methods:

• Interpreting development as a series of evolutionarily independent stages.
• Defining homology based on similarity and the complexity of characters.
• Critically analyzing topology as a homology assessment tool.
• Applying complexity as a test for homology in developmental contexts.

Main Results:

• Developmental stages should not be prioritized over character complexity in homology assessments.
• Complexity, defined as the potential for subdividing a character into independent substructures, is a robust test for homology.
• Topology is an unreliable indicator of homology due to the non-indicative nature of corresponding positions.
• Homologizing developmental stages and processes are distinct approaches that should not be conflated.

Conclusions:

• A homology definition incorporating similarity and complexity is favored.
• Complexity serves as a key test for homology, allowing subdivision into independent substructures.
• The distinction between homologizing developmental stages versus processes is crucial.
• There is no singular "ontogenetic homology criterion"; rather, complexity is the primary assessment tool.