Chapter 7 Key Takeaways

The Framework

1. Darwin identified two mechanisms of selection relevant to mating. Natural selection shapes survival; sexual selection shapes mating success through intrasexual competition (same-sex rivals competing) and intersexual choice (one sex preferentially selecting among members of the other). Understanding attraction requires both.

2. Parental investment theory provides evolutionary psychology's most powerful predictive engine. Trivers (1972) showed that the higher-investing sex in any species will be more selective about mates and less competitive; the lower-investing sex will be more competitive and less selective. In most mammals, including humans, females invest more — but this is a framework about investment structure, not a fixed rule about sex.

3. Honest signals are physical or behavioral traits that reliably indicate underlying quality because they are costly to produce. Symmetry, health indicators, and certain sex-typical physical features may function as honest signals — but effect sizes are often modest, and most people respond to them without conscious awareness of what they are detecting.

The Evidence

4. Buss's cross-cultural mate preference research found consistent patterns across 37 cultures — but "consistent" requires careful qualification. The patterns are real in terms of direction (men weight physical attractiveness more; women weight resources more), but the magnitude of these differences varies enormously across cultures. Eagly and Wood showed that sex differences are smaller in more gender-equal societies, suggesting social conditions modulate evolved tendencies substantially.

5. The WEIRD-sample problem is acute in evolutionary mating research. Most studies have sampled from Western, Educated, Industrialized, Rich, Democratic populations. The few studies on genuinely diverse populations — including forager societies like the Hadza — often find different patterns. Universality claims require universal sampling.

6. Several high-profile evolutionary predictions have failed to replicate. The ovulatory-cycle-shift effect — claimed to show women prefer more masculine men during fertile phases — largely collapsed under rigorous replication attempts. This is an important case study in the Replication Crisis applied to evolutionary psychology.

The Critiques

7. The just-so story problem is real and methodologically serious. When an evolutionary framework can accommodate almost any empirical finding after the fact, it is not functioning as a rigorous scientific theory. Good evolutionary explanations require specific, falsifiable predictions that distinguish them from alternative accounts.

8. Feminist evolutionary scholars have reformed the field, not rejected it. Sarah Blaffer Hrdy, Cordelia Fine, and Anne Fausto-Sterling work within evolutionary and biological frameworks while challenging the selective, male-centered narratives that dominated the field's early decades. Their work is a model of good-faith scientific critique.

9. Female mating behavior is more complex, strategic, and agentive than the standard model assumed. Hrdy's research demonstrated that female primates — including humans — are active agents whose reproductive strategies extend well beyond passive mate-quality assessment to include coalition-building, polyandrous paternity confusion, and cooperative breeding networks.

The Limits

10. Evolutionary psychology cannot explain individual variation, rapid cultural change, or non-heterosexual sexuality adequately. The field describes species-typical tendencies, not individual destinies. Cultural change in mating patterns operates far faster than genetic selection can explain. Same-sex attraction remains under-theorized within standard frameworks.

11. Evolutionary explanation does not carry prescriptive force. Even accurate descriptions of evolved tendencies carry no obligation to act them out. The naturalistic fallacy — "natural, therefore good" — is always a logical error. Understanding our evolutionary heritage gives us more choices, not fewer.

Chapter 7 is the primary chapter for the Nature vs. Nurture theme. See Chapter 10 for personal reflection on nature/nurture experience, and Chapter 8 for the empirical attractiveness literature in detail.