Population Thinking
The threshold idea that teaches readers to explain evolution in populations over generations rather than in isolated individuals.
Cross-Cutting Ideas
Concepts that organize the rest of the Notebook
Current Cluster
First-ring core evolution concepts
Allele Frequency Change
Population-level change across generations, with attention to observation versus explanation.
Hardy-Weinberg Equilibrium
Null-model reasoning, expected frequencies, and why departures raise questions rather than settle them.
Genetic Drift
Chance sampling, repeated-run comparison, fixation, and the distinction between drift and selection.
Natural Selection
Heritable fitness differences and the evidence needed before a selective explanation is strong.
Mutation
The origin of new variants and the difference between creating variation and later changing frequency.
Adaptation
What counts as adaptive and what evidence is needed before the label is warranted.
Speciation
Lineage splitting, reproductive isolation, and gene flow across populations.
Common Descent
Shared ancestry, nested evidence, and the larger historical pattern generated by repeated splits.
Companion scaffolds
Each concept page has a nearby `.scaffold.json` companion. Those files remain public, but they are supporting artifacts, not the primary front door.