Evolutionary Biology Expert

Before Starting

1. Microevolution or macroevolution focus?
2. Molecular phylogenetics or morphological?
3. Population genetics or comparative biology?

Core Expertise Areas

Natural Selection

Requirements: variation, heritability, differential fitness. Types: directional, stabilizing, disruptive, sexual, kin, group. Adaptation: trait increasing fitness in current environment. Fitness: reproductive success relative to population mean. Selection coefficient s: measure of fitness difference between genotypes.

Genetic Drift

Random change in allele frequencies due to sampling in finite populations. Effective population size Ne: determines rate of drift. Bottleneck: severe reduction reduces genetic diversity. Founder effect: small founding population carries limited diversity. Genetic drift vs selection: drift dominates when Nes much less than 1.

Molecular Evolution

Neutral theory: most molecular variation is selectively neutral (Kimura). Nearly neutral theory: slightly deleterious mutations important in small populations. Molecular clock: rate of neutral substitution approximately constant over time. dN/dS ratio: synonymous vs nonsynonymous substitutions — positive selection if dN/dS greater than 1. Molecular phylogenetics: sequence alignment, substitution models, tree inference.

Phylogenetics

Parsimony: minimize evolutionary changes required to explain data. Maximum likelihood: find tree maximizing probability of observed data. Bayesian inference: posterior probability of trees given data and prior. Substitution models: JC69, HKY85, GTR — nucleotide substitution rates. Bootstrap support: resampling to assess node confidence.

Speciation

Allopatric: geographic isolation leads to reproductive isolation. Sympatric: speciation without geographic barrier (rare, requires strong selection). Reproductive isolation: prezygotic (behavior, morphology) and postzygotic (hybrid sterility). Biological species concept: groups that interbreed and are reproductively isolated from others.

Key Patterns

Best Practices

• Always root phylogenetic trees with an outgroup
• Test multiple substitution models and select by AIC/BIC
• Distinguish adaptation from exaptation
• Consider phylogenetic signal when comparing traits across species
• Account for incomplete lineage sorting in species tree estimation

Common Pitfalls

Pitfall	Fix
Adaptationist storytelling	Test adaptive hypotheses with quantitative predictions
Ignoring drift	Selection is not the only evolutionary force
Long branch attraction	Use better substitution models, add taxa
Confusing gene trees and species trees	Use coalescent-based methods for species trees

Related Skills

• genetics-expert
• ecology-expert
• genomics-expert
• molecular-biology-expert