Model Adequacy and Microevolutionary Explanations for Stasis in the Fossil Record

Area of Science:

• Evolutionary Biology
• Paleontology
• Macroevolution

Background:

• Long-term phenotypic stasis is a common pattern in the fossil record.
• Microevolutionary theory struggles to predict or explain macroevolutionary stasis.
• Accurate evolutionary models are needed to understand trait dynamics over long timescales.

Purpose of the Study:

• To develop and apply tests for assessing the adequacy of common evolutionary stasis models.
• To investigate potential explanations for phenotypic stasis in fossil lineages.
• To evaluate the fixed-optimum hypothesis using empirical data from fossil time series.

Main Methods:

• Developed statistical tests to evaluate the fit of evolutionary stasis models.
• Analyzed 572 time series of phenotypic traits from published fossil lineages.
• Compared stasis model fit against alternative models and assessed parameter estimates.

Main Results:

• Of 572 analyzed time series, 263 showed a better fit to the stasis model.
• Only 172 time series adequately fitted the stasis model in both relative and absolute terms.
• Estimated trait variances did not correlate with proxies for effective population size, challenging the fixed-optimum hypothesis.

Conclusions:

• The fixed-optimum hypothesis, driven by genetic drift, lacks empirical support as a primary explanation for stasis in the fossil record.
• Optima evolving via stationary processes on the adaptive landscape presents a viable alternative hypothesis for stasis.
• Model adequacy testing is crucial for advancing our understanding of adaptive landscape dynamics in macroevolution.