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Human evolution isn't just a story—it's a scientific argument built from competing theories, each offering different explanations for how, when, and why we became the species we are today. You're being tested on your ability to distinguish between these frameworks: understanding whether a theory addresses mechanisms of change (how evolution works at the genetic or population level), geographic patterns (where modern humans originated), or selective pressures (what environmental or social forces drove specific adaptations like bipedalism or brain expansion).
These theories don't exist in isolation—they overlap, compete, and sometimes complement each other. The best exam responses demonstrate that you can evaluate evidence critically and apply the right theoretical framework to explain specific hominin traits or fossil patterns. Don't just memorize names and dates—know what type of question each theory answers and what evidence supports or challenges it.
These foundational theories explain how evolution operates at the biological level—the engines driving change across generations. Natural selection, genetic drift, and tempo of change are the core concepts here.
Compare: Darwin's natural selection vs. Neutral Theory—both explain genetic change over time, but natural selection emphasizes adaptive change while neutral theory highlights random change at the molecular level. FRQs may ask you to explain when each mechanism dominates.
These competing theories address a fundamental question: where did anatomically modern humans evolve, and how did we spread across the globe? The genetic and fossil evidence you'll encounter on exams directly tests these models.
Compare: Out of Africa vs. Multiregional—both explain modern human diversity, but they differ on when and where that diversity originated. Recent ancient DNA evidence (showing ~2% Neanderthal ancestry in non-Africans) suggests a modified Out of Africa model with some interbreeding—know this nuance for FRQs.
What selective pressures shaped distinctly human traits? These hypotheses propose specific environmental contexts that favored bipedalism, thermoregulation, and other adaptations. Habitat reconstruction and paleoclimate data are key evidence types.
Compare: Savannah vs. Aquatic Ape—both attempt to explain bipedalism and body form, but savannah hypothesis has stronger paleoenvironmental support. If asked to evaluate competing hypotheses, emphasize testability and fossil context as criteria.
Why did hominin brains expand so dramatically? These theories focus on the selective advantages of intelligence, linking brain evolution to social complexity, diet, and technology.
Compare: Social Brain vs. Cooking Hypothesis—these aren't mutually exclusive. Social demands may explain why bigger brains were advantageous, while cooking explains how the metabolic costs of brain expansion were met. Strong FRQ answers integrate multiple hypotheses.
This theory addresses cellular evolution long before hominins—but understanding it helps you place human evolution within the broader tree of life.
| Concept | Best Examples |
|---|---|
| Mechanisms of change | Natural Selection, Punctuated Equilibrium, Neutral Theory |
| Geographic origins | Out of Africa, Multiregional Hypothesis |
| Environmental pressures | Savannah Hypothesis, Aquatic Ape Hypothesis |
| Cognitive evolution | Social Brain Hypothesis, Cooking Hypothesis |
| Molecular evidence applications | Neutral Theory, Out of Africa (genetic diversity) |
| Cultural-biological interaction | Cooking Hypothesis |
| Tempo of evolution | Punctuated Equilibrium vs. Gradualism (Darwin) |
| Cellular evolution | Endosymbiotic Theory |
Which two theories offer competing explanations for the geographic origins of modern humans, and what genetic evidence helps distinguish between them?
How do natural selection and genetic drift differ as mechanisms of evolutionary change? Under what conditions might drift be more influential than selection?
Compare the Savannah Hypothesis and the Aquatic Ape Hypothesis as explanations for bipedalism—what types of evidence would you need to evaluate each?
If an FRQ asks you to explain the rapid increase in hominin brain size, which two hypotheses would you combine, and how do they complement each other?
Why does the Out of Africa model predict greater genetic diversity within African populations than outside Africa? How does this prediction differ from what the Multiregional Hypothesis would predict?