Case Study 2: Evolutionary Psychology Claims — Science or Just-So Stories?

The Framework

Evolutionary psychology (evo-psych) applies evolutionary theory to human behavior and cognition. The core premise: the human mind, like the human body, was shaped by natural selection. Our psychological tendencies — including mate preferences — reflect adaptations to ancestral environments.

This premise is scientifically sound in principle. The human brain did evolve, and evolutionary pressures did shape our psychology. The question is not whether evolution influenced human behavior (it did) but whether specific evo-psych claims about mate preferences are supported by evidence or are unfalsifiable adaptive stories.

Claims and Evidence

Claim 1: "Men universally prefer younger women because youth signals fertility"

Evidence: Buss (1989) found that men across 37 cultures preferred younger partners (on average, about 2.5 years younger). This is one of the most consistent cross-cultural findings in evo-psych.

Complications: - The preference is real but modest — 2.5 years, not the dramatic age gaps the pop version implies - In cultures with greater gender equality, the age preference gap narrows - The preference may partly reflect cultural norms (younger women having less social power) rather than purely biological fitness signals - Modern reproduction technology (IVF, egg freezing) has decoupled age from fertility, yet the preference persists — which could support either biological hardwiring or cultural lag

Rating: ⚠️ OVERSIMPLIFIED — The average preference exists but is modest, culturally modulated, and may not be purely about fertility signaling.

Claim 2: "Women universally prefer high-status, resource-rich men because resources signal provision ability"

Evidence: Buss (1989) found that women across cultures valued earning potential more than men did. Some studies find women prefer taller, older men with social status.

Complications: - As women's economic independence increases, the preference for male resources weakens (Eagly & Wood, 1999). In highly gender-equal countries like Norway and Sweden, the sex difference in resource preference virtually disappears - This strongly suggests the preference is partly a rational response to economic dependence (if you can't earn, you need a partner who can), not purely a hardwired adaptation - Individual variation is enormous — many women prioritize humor, kindness, or shared interests over earning potential

Rating: ⚠️ OVERSIMPLIFIED — The average preference exists but is substantially explained by economic context, shrinks with gender equality, and shows enormous individual variation.

Claim 3: "Men prefer a 0.7 waist-to-hip ratio because it signals health and fertility"

Evidence: Singh (1993) found that men across cultures preferred women with a WHR of approximately 0.7. The finding was widely cited and became a staple of evo-psych popularization.

Complications: - Replications have been inconsistent. Some cross-cultural studies find the 0.7 preference; others don't - Preferences for body type vary significantly across cultures and historical periods. The "ideal" body shape in Rubens paintings, in many African cultures, and in contemporary Samoa is very different from the 0.7 WHR preference - Yu and Shepard (2012) found that among the Matsigenka of Peru (a foraging society closer to ancestral conditions), the "universal" WHR preference was absent — men preferred higher WHRs - The methodological quality of the original studies has been questioned

Rating: ⚠️ OVERSIMPLIFIED to 🔬 UNRESOLVED — Some evidence exists, but cross-cultural variation is significant, and the "universal hardwired" framing is not supported.

Claim 4: "Humans can detect genetic compatibility through pheromones (the sweaty t-shirt study)"

Evidence: Wedekind et al. (1995) found that women preferred the body odor of men whose MHC (major histocompatibility complex) genes were different from their own — suggesting that smell signals immune system compatibility.

Complications: - The study was small (49 women rating 6 t-shirts each) - Replications have been inconsistent — some find the effect, some don't - The effect disappears for women on hormonal contraception - The practical significance is unclear — even if the effect is real, it's tiny and would be swamped by other factors in actual mate selection

Rating: 🔬 UNRESOLVED — Interesting but unreliably replicated and of uncertain practical significance.

The "Just-So Story" Problem

The deepest criticism of evolutionary psychology mate preference claims is that many are unfalsifiable just-so stories. Here's the test:

For any observed preference, can you construct an equally plausible adaptive story for the opposite preference? If so, the evolutionary explanation doesn't actually explain anything — it just provides a post-hoc narrative.

Example: "Men prefer younger women because youth signals fertility." Opposite story: "Men should prefer older women because they have demonstrated survival ability, have more resources, and have proven fertility (they've already had children)."

Both stories are equally plausible as adaptive explanations. The fact that you can tell both means neither one is truly explanatory — they're both stories about why evolution would produce whatever preference is observed. This is the hallmark of unfalsifiable reasoning.

The Balanced View

Evolutionary psychology's core premise is sound: evolution shaped human psychology, including some aspects of mate preferences.

Some cross-cultural patterns are real: Average sex differences in certain preference dimensions (attractiveness, resources) have been documented repeatedly, though with important cultural modulation.

The pop version dramatically overstates the "hardwired" aspect: Cultural context, individual variation, and gender equality all substantially modulate the preferences. The strong form ("evolution has programmed you to...") is not supported.

Many specific claims are just-so stories: Without clear, testable predictions that distinguish evolutionary from cultural explanations, many evo-psych claims about mate preferences are adaptive narratives, not science.

Discussion Questions

  1. How would you design a study that could distinguish between evolutionary and cultural explanations for a mate preference? Is this even possible?

  2. As gender equality increases, sex differences in mate preferences shrink. Does this support the cultural or the evolutionary explanation — or could both be operating?

  3. Pop evo-psych is often used to justify gender stereotypes ("men are hardwired to..."). How should researchers respond when their findings are used this way?

  4. The sweaty t-shirt study is widely cited despite inconsistent replications. Why do some findings become culturally embedded despite weak evidence? (Consider: the finding is dramatic, romantic, and reinforces the idea that love is biological.)