Case Study 2: Evolutionary Just-So Stories and the Limits of Adaptation Narratives

The Challenge

Evolutionary psychology faces a unique version of the plausible story problem: for virtually any human behavior, trait, or preference, a plausible evolutionary explanation can be constructed after the fact. The explanations draw on real principles (natural selection, sexual selection, kin selection) and apply them to observed behaviors with narrative coherence.

The question is whether these explanations are genuine discoveries about human evolution or post-hoc stories that could equally well explain any behavior.

Three Examples

Why Do Humans Like Music?

Evolutionary story A: Music was sexually selected. Musical ability demonstrated cognitive complexity, creativity, and motor coordination — traits that indicated genetic fitness. Individuals who could produce and appreciate music attracted better mates. (Darwin proposed a version of this.)

Evolutionary story B: Music enhanced group cohesion. Groups that sang together coordinated better, fought more effectively, and maintained stronger social bonds. Musical capacity was selected because it improved group survival. (Multiple researchers have proposed this.)

Evolutionary story C: Music is not an adaptation at all. It is a byproduct ("spandrel") of cognitive capacities that evolved for other purposes — language processing, pattern recognition, emotional regulation. Music activates these systems in ways that produce pleasure, but it was never specifically selected for. (Steven Pinker proposed this view, calling music "auditory cheesecake.")

All three stories are plausible. All three use real evolutionary principles. All three are consistent with the available evidence. And the evidence currently available cannot distinguish between them. This is underdetermination in action.

Why Are Humans Afraid of Snakes?

Story A (prepared fear): Ancestral humans who feared snakes were more likely to survive because snakes were a genuine threat. Natural selection favored a prepared fear response — a low threshold for snake detection and fear activation.

This is one of evolutionary psychology's most well-supported claims. Studies have shown that humans (including infants) detect snake images faster than other stimuli, and that snake phobias are easier to condition than fears of modern dangers (cars, electrical outlets). The evidence includes cross-cultural data, developmental data, and neuroimaging data.

Why this works: The snake fear claim makes specific, testable predictions (faster detection, easier conditioning, cross-cultural universality) that have been tested and partially confirmed. It is not merely a plausible story — it has passed the prediction test.

Why Do Humans Gossip?

Story A: Gossip is a social grooming mechanism that replaced physical grooming as group sizes increased. It maintains social bonds, enforces norms, and tracks reputational information — all fitness-relevant functions.

Story B: Gossip is a form of social intelligence that evolved to navigate complex alliance structures. Tracking who did what to whom enables strategic social behavior.

Story C: Gossip is a mechanism for enforcing cooperation through reputation. Groups that gossip punish free-riders and cheaters, maintaining the cooperative framework that benefits the group.

All three stories are plausible. All are consistent with the evidence. None has been tested in a way that distinguishes it from the others.

The Diagnostic

The snake fear case shows what a testable evolutionary claim looks like: it makes specific predictions about detection speed, conditioning ease, and cross-cultural presence — and those predictions can be (and have been) tested.

The music case and the gossip case show what untestable evolutionary claims look like: multiple plausible stories, each consistent with the evidence, none generating predictions that would distinguish between them.

The dividing line is not between "evolutionary" and "non-evolutionary" explanations. It is between explanations that make testable predictions and explanations that only accommodate existing observations.

The Just-So Story Checklist

For any evolutionary explanation, apply these tests:

  1. Prediction test: Does this explanation predict something we haven't yet observed? If not, it may be post-hoc.
  2. Alternative story test: Can an equally plausible evolutionary story reach the opposite conclusion? If yes, the evidence is underdetermined.
  3. Non-evolutionary alternative test: Can a non-evolutionary explanation (cultural learning, individual development, byproduct of other adaptations) account for the same behavior? If yes, the evolutionary story isn't the only game in town.
  4. Cross-cultural test: Does the behavior show the cross-cultural universality predicted by an evolutionary explanation? If not, cultural variation may be more important than evolutionary heritage.

Discussion Questions

  1. Apply the just-so story checklist to the claim that "men are naturally more aggressive than women because of sexual selection."
  2. Stephen Jay Gould and Richard Lewontin criticized adaptationism — the tendency to assume every trait is an adaptation — in their famous "spandrels" paper. How does their critique relate to the plausible story problem?
  3. Is it possible to do evolutionary psychology without just-so stories? What would methodologically rigorous evolutionary psychology look like?
  4. The chapter argues that "plausible" is not the same as "supported." But in fields where experiments are impossible (we can't re-run human evolution), is plausibility the best we can achieve?

References

  • Gould, S. J. & Lewontin, R. C. (1979). "The Spandrels of San Marco and the Panglossian Paradigm." Proceedings of the Royal Society of London B, 205(1161), 581–598. (Tier 1)
  • Pinker, S. (1997). How the Mind Works. W. W. Norton. (Tier 1 — includes the "auditory cheesecake" argument)
  • Research on prepared fears (snakes, spiders) has been conducted by multiple research groups, including Öhman and Mineka's work on fear conditioning. (Tier 2)
  • Sober, E. (2000). "Testability." Proceedings and Addresses of the American Philosophical Association, 73(2). (Tier 1 — on the testability of evolutionary claims)