Evolution and Human Behavior

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A Brief Overview of Some Classic Ideas in Evolutionary Theory:

System Level / Problem
Investigator / Year of Publication
Basic ideas
Example Adaptations

System Level: Individual
Problem: How to survive?
Charles Darwin (1859)

Natural Selection (or “survival selection”): The bodies and minds of organisms are made up of evolved adaptations designed to help the organism survive in a particular ecology (for example, the white fur of polar bears).

Bones, skin, vision, pain perception, etc.



System Level: Dyad
Problem: How to attract a mate and/or compete with members of one's own sex for access to the opposite sex?
Charles Darwin (1859)

Sexual selection: Organisms can evolve physical and mental traits designed specifically to attract mates (e.g., the Peacock’s tail) or to compete with members of one’s own sex for access to the opposite sex (e.g., antlers). In most species, the effects of sexual selection are seen in males since they typically have a faster reproductive rate than do females.

Peacock’s tail, antlers, courtship behavior, etc


System Level: Family & Kin
Problem: Gene replication. How to help those with whom we share genes survive and reproduce?
William Hamilton (1964)

Inclusive fitness (or a "gene’s eye view" of selection, "kin selection") / The evolution of sexual reproduction: Selection occurs most robustly at the level of the gene, not the individual, group, or species. Reproductive success can thus be indirect, via shared genes in kin. Being altruistic toward kin can thus have genetic payoffs. Also, Hamilton argued that sexual reproduction evolved primarily as a defense against pathogens (bacteria & viruses) to "shuffle genes" to create greater diversity, especially immunological variability, in offspring.

Altruism toward kin, parental investment, the behavior of the social insects with sterile workers (e.g., ants).



System Level: Dyad / Family & Kin
Problem: How to allocate resources among offspring to maximize reproductive output?
Robert Trivers (1972)

Parental Investment Theory / Parent - Offspring Conflict / Reproductive Value : The two sexes often have conflicting strategies regarding how much to invest in offspring, and how many offspring to have.
Parents allocate more resources to their offspring with higher reproductive value (e.g., "mom always liked you best"). Parents and offspring may have conflicting interests (e.g., when to wean, allocation of resources among offspring, etc.).
Sexually dimorphic adaptations that result in a "battle of the sexes," parental favoritism, timing of reproduction, parent-offspring conflict, sibling rivalry, etc.

System Level:Non-Kin Small Group
Problem: How to succeed in competitive interactions with non-kin? How to select the best strategy given the strategies being used by competitors?
von Neumann and Morgenstern (1944);Maynard Smith (1982)

Game Theory / Evolutionary Game Theory : Organisms adapt, or respond, to competitors depending on the strategies used by competitors. Strategies are evaluated by the probable payoffs of alternatives. In a population, this typically results in an "evolutionary stable strategy," or "evolutionary stable equilibrium" -- strategies that, on average, cannot be bettered by alternative strategies.
Facultative, or frequency-dependent, adaptations. Examples: hawks vs. doves, cooperate vs. defect, fast vs. coy courtship, etc.

System Level:Non-Kin Small Group
Problem: How to maintain mutually beneficial relationships with non-kin in repeated interactions?
Robert Trivers (1971)

"Tit for Tat" Reciprocity: One can play nice with non-kin if a mutually beneficially reciprocal relationship is maintained across multiple social interactions, and cheating is punished.
Cheater detection, emotions of revenge and guilt, etc.

System Level:Non-Kin, Large Groups Governed by Rules / Laws
Problem: How to maintain mutually beneficial relationships with strangers with whom one may interact only once?
Herbert Gintis (2000, 2003); and others.

Generalized Reciprocity(Also called "strong reciprocity"): One can play nice with non-kin strangers even in single interactions if social rules against cheating are maintained by neutral third parties (e.g., other individuals, governments, institutions, etc.), a majority group members cooperate by generally adhering to social rules, and social interactions create a positive sum game (i.e., a bigger overall "pie" results from group cooperation).
Generalized reciprocity may be a set of adaptations that were designed for small in-group cohesion during times of high inter-tribal warfare with out-groups.Today the capacity to be altruistic to in-group strangers may result from a serendipitous generalization (or "mismatch") between ancestral tribal living in small groups and today's large societies that entail many single interactions with anonymous strangers. (The dark side of generalized reciprocity may be that these adaptations may also underlie aggression toward out-groups.)
To in-group members:
Capacity for generalized altruism, acting like a "good Samaritan," cognitive concepts of justice, ethics and human rights.To out-group members:
Capacity for xenophobia, racism, warfare, genocide.


System Level:Large groups / culture.
Problem:How to transfer information across distance and time?
Richard Dawkins (1976)

Memetic Selection: Genes are not the only replicators subject to evolutionary change. “Memes” (e.g., ideas, rituals, tunes, cultural fads, etc.) can replicate and spread from brain to brain, and many of the same evolutionary principles that apply to genes apply to memes as well. Genes and memes may at times co-evolve ("gene-culture co-evolution").
Language, music, evoked culture, etc. Some possible by-products, or "exaptations," of language may include writing, reading, mathematics, etc.


Table from Mills, M.E. (2004). Evolution and motivation. Symposium paper presented at the Western Psychological Association Conference, Phoenix, AZ. April, 2004.