Module 12: Evolutionary Psychology: Explaining Human Nature and Nurture

Evolutionary Psychology: Core Ideas

Evolutionary psychology applies Charles Darwin’s principle of natural selection to understand the roots of behavior and mental processes.
The field asks why humans are so similar in many ways, rather than focusing solely on differences.
Natural selection is the process by which inherited traits that better enable survival and reproduction in a given environment are more likely to be passed to future generations, shaping population characteristics over time.

Natural Selection and Adaptation

Natural selection: inherited traits that better enable an organism to survive and reproduce in a particular environment will (in competition with other trait variations) most likely be passed on to succeeding generations.
Adaptation: traits shaped by natural selection that increase fitness (survival and reproduction) in a given environment.
The environment imposes selective pressures that favor certain variations over others.

Genes, Variation, and Mutation

Variation arises from new gene combinations produced at conception and occasional random mutations (random errors in gene replication that become nature’s prelimary tests of alternative possibilities).
The tight genetic leash differs among species: humans have a looser leash than many other species (e.g., dogs, cats, birds) but still show strong heritable tendencies.
Genes plus experience together wire the brain; adaptive flexibility enables learning and adaptation to varied environments.
Fitness is defined by an organism’s ability to survive and reproduce in its environment.

Human Genetic Variation: Within vs Between Populations

Our similarities arise from a shared human genome.
No more than 5\% of the genetic differences among humans arise from population group differences; about 95\% of genetic variation exists within populations (Rosenberg et al., 2002).
The typical genetic difference between two individuals from within one population (e.g., two South Africans or two Singaporeans) is often greater than the average difference between the two groups.
If a worldwide catastrophe left only one population surviving (e.g., only South Africans or only Singaporeans), the human species would suffer only a trivial reduction in genetic diversity (Lewontin, 1982).

Our Shared Genomic Legacy and Early Adaptations

Early humans faced key questions: Who is my ally? Who is my foe? With whom should I mate? What food should I eat?
Those who answered these questions more successfully contributed genes to future generations.
For example, women who experienced nausea during the first three months of pregnancy were genetically predisposed to avoid certain bitter, strongly flavored, and novel foods; these foods are often toxic to prenatal development (Profet, 1992; Schmitt & Pilcher, 2004).
Those who mated and nurtured offspring successfully tended to pass on their genes; unsuccessful mating or nurturing tended to be lost from the gene pool.
Across cultural differences, humans share a universal moral grammar (Mikhail, 2007). For example, most people respond negatively to a scenario where sacrificing one person to save seven is considered; and respond more approvingly to sacrificing the seven by causing the one to fall into the vent. These tendencies reflect a cultural- and species-wide moral framework rooted in evolution.
Over generations, these success-enhancing genes produced behavioral tendencies and learning capacities that helped Stone Age ancestors survive, reproduce, and pass genes forward.
Despite high infant mortality and disease in past millennia, our lineage’s reproductive success ensured descendants; we are the product of long runs of successful reproduction.

Shared Psychology and Moral Intuitions Across Cultures

There is a universal set of moral intuitions about harm and killing that transcends culture, suggesting deep evolutionary roots in social behavior and punishment for direct harm.
These universal tendencies help explain why humans across diverse environments share common social rules and emotional responses.

Adaptation, Mismatch, and Modern Life

Humans are not blank slates; we are genetically predisposed to think and act in ways that promoted our ancestors’ survival and reproduction.
However, many evolved dispositions are mismatched with modern environments (e.g., a strong preference for sweets and fats due to ancestral food scarcity).
Our deeply rooted predispositions can lead to maladaptive outcomes in today’s abundance of junk food and sedentary lifestyles, illustrating the mismatch between evolved tendencies and contemporary contexts.

Darwinian Revolution and Psychology Today

Darwin’s theory is a fundamental organizing principle in biology that continues to influence psychology (the second Darwinian revolution): applying evolutionary principles to human behavior and mental processes.
Darwin anticipated this shift: “open fields for far more important researches. Psychology will be based on a new foundation.” (Darwin, 1859, p. 346).
Some scholars view science and religion as potentially complementary rather than conflicting, with science explaining the when and how of phenomena and religion offering ultimate questions of why.
Galileo’s famous line illustrates this stance: the Bible teaches how to go to heaven, not how the heavens go.
Evolutionary psychology raises questions such as: Why do infants fear strangers when they become mobile? Why do more people develop specific phobias (spiders, snakes, heights) than to modern threats (guns)? Why do we fear commercial air travel more than riskier driving?

Domestication as an Experimental Model: The Foxes (Belyaev and Trut)

Idea: If humans could domesticate a wild wolf into a friendly dog-like fox, could a similar transformation happen in a comparatively short time?
Dmitry Belyaev (early 1950s) initiated an experimental program to domesticate foxes toward tameness.
Experimental design and results:
- Starting population: 100 female and 30 male foxes selected from fox farms.
- Selection criteria: tameness measured by foxes’ responses to feeding, handling, and being stroked.
- Breeding plan: from offspring, select and mate the tamest 20% of females and 5% of males.
- Time span: maintained for 57 generations over 40 years.
- Scale: about 45,000 foxes bred in the program.
- Outcome: after decades, a new breed emerged, described by Trut (1999) as docile, eager to please, and unmistakably domesticated; aggression toward humans diminished and affiliative behaviors increased (e.g., whimpering for attention, licking as a dog-like gesture).
The program demonstrates artificial selection rather than natural selection, highlighting dynamics of trait changes under directed breeding.
The project was later leveraged to market friendlier foxes as potential pets due to their human-compatibility traits (Courtesy Institute of Cytology and Genetics, SB RAS).

RP-1: Retrieval Practice and Evolutionary Methods

Question: How are Belyaev and Trut’s breeding practices similar to, and how do they differ from, the way natural selection normally occurs?
Brief answer (APPENDIX E):
- Similarities: both involve selection for traits that affect survival or reproduction and can lead to rapid changes in a population.
- Differences: Belyaev and Trut used deliberate, human-guided selection (artificial selection) focusing on tameness, a non-random and environment-specified criterion, typically resulting in faster changes than natural selection would under historical environmental pressures; natural selection usually acts on traits that influence fitness in fluctuating environmental conditions without specific human goals.

Quantitative Data and References (Key Numbers and Citations)

No more than 5\% of genetic differences among humans arise from population group differences; about 95\% of genetic variation exists within populations (Rosenberg et al., 2002).
The typical genetic difference between two individuals from within populations (e.g., two South Africans vs two Singaporeans) can exceed the average difference between the groups.
If only one population survived a catastrophe (e.g., only South Africans or only Singaporeans), genetic diversity would decline only modestly: a “trivial reduction” (Lewontin, 1982).
Our shared genome and the story of human evolution involve natural selection acting over long timescales, with occasional mutations providing fresh variation (Profet, 1992; Schmitt & Pilcher, 2004).
Belyaev and Trut’s fox domestication program: starting with 100 female and 30 male foxes; selection of 20% of females and 5% of males; 57 generations; 40 years; about 45{,}000 foxes (Dugatkin & Trut, 2017; Trut, 1999).
Classic works and voices cited: Darwin (1859); Galileo (contextual reference); Christakis (2019); Mikhail (2007); Rosenberg et al. (2002); Lewontin (1982); Profet (1992); Schmitt & Pilcher (2004).

Connections to Prior Learning and Real-World Relevance

Evolutionary principles underlie many everyday human behaviors, including sociality, parenting, and moral judgement.
Understanding the mismatch between evolved dispositions and modern environments informs public health, education, and policy (e.g., nutrition, risk perception).
Studying domestication experiments provides a tangible model for how selection pressures shape behavior and anatomy over generations, illustrating the power and limits of selection in driving phenotype changes.

Ethical, Philosophical, and Practical Implications

Evolutionary explanations help illuminate why humans share universal traits while also explaining the variability across cultures.
The compatibility perspective encourages dialogue between science and religion, rather than conflict, by acknowledging complementary insights about life’s origins and purposes.
Practical implications include recognizing the influence of inherited predispositions on behavior while also acknowledging the role of environment, learning, and cultural practices in shaping outcomes.

Summary of Key Concepts

Evolutionary psychology explains human nature through natural selection and genetic predispositions shaped by ancestral environments.
Humans show vast genetic similarity across populations, with most variation found within populations rather than between them.
Our modern behaviors are influenced by evolved tendencies that sometimes misalign with present-day environments (mismatch).
Experimental domestication (e.g., foxes) demonstrates how directed selection can reshape behavior and morphology over generations.
Ongoing scholarly discussions link scientific explanations with broader philosophical and religious questions about meaning and purpose.