The Comparative Method is Not Macroevolution: Across-Species Evidence for Within-Species Process.

Area of Science:

• Evolutionary Biology
• Population Genetics
• Comparative Biology

Background:

• The comparative method, documenting across-species trait correlations, is frequently labeled "macroevolutionary."
• This designation stems from definitions of macroevolution as "evolution above the species level."

Purpose of the Study:

• To argue that labeling comparative studies of adaptation as "macroevolutionary" is detrimental.
• To highlight how this misnomer obscures the population-level causal mechanisms of adaptation.
• To emphasize the importance of studying adaptation as a population-level phenomenon.

Main Methods:

• Analysis of the conceptual underpinnings of the comparative method in evolutionary studies.
• Critique of the application of the term "macroevolution" to comparative analyses of adaptation.
• Examination of adaptation as a population-level process involving heritable variation and fitness differences.

Main Results:

• The comparative method tests hypotheses about population-level natural selection, not necessarily macroevolutionary processes.
• Observed trait-environment correlations across species (e.g., streamlined aquatic animals) reflect adaptation driven by selection on heritable variation.
• Developmental dynamics at the individual level also influence the variation available for selection, further grounding adaptation in non-macroevolutionary processes.

Conclusions:

• Designating comparative studies of adaptation as "macroevolutionary" is misleading and harmful.
• This terminology obscures the actual population-level processes, such as natural selection and developmental constraints, that drive adaptation.
• Future research should focus on testing adaptation hypotheses and understanding developmental influences rather than relying on the "macroevolutionary" label.