Nature & Nurture, Behavior Genetics and Evolutionary Psychology
Nature & Nurture: Behavior Genetics and Evolutionary Psychology
The Nature/Nurture "Debate" Reframed
Definition of Terms:
Nature: Refers to genetics, traits, and predispositions inherited from parents.
Nurture: Refers to the components of our environment, including experiences, upbringing, and external factors.
Beyond a Debate:
The idea of a "debate" is a misnomer; scientists acknowledge that psychology is a complex interaction of both nature and nurture.
This interaction extends beyond psychology to biology, medicine, and other fields.
Gene Predisposition and Environmental Triggers:
Often, an individual may have a genetic predisposition to certain conditions (e.g., depression, skin cancer, alcoholism).
However, the condition's expression is typically triggered by environmental factors (e.g., behavior, pollutants, stress).
Crucially, possessing a gene for a condition does not guarantee its expression.
The Dynamic Interplay of Nature and Nurture
Impact of Environmental Similarity/Difference:
As environments become more similar, people tend to become more similar.
As environments become more different, people tend to become more different.
Relative Importance of Nature:
When environments are very similar, nature becomes more significant in explaining individual differences.
Conversely, when environments are very different, nature becomes less important in explaining differences, as environmental factors play a larger role.
Application to Exam-Type Questions:
(1) Identically Raised Individuals with Math Skill Differences: If two people are raised identically but show differences in math skills, nature probably plays a mostly dominant role in these differences because the environmental (nurture) variables are controlled.
(2) Identical Twins with Math Skill Differences: If two identical twins (sharing 100\% of genes) show differences in math skills, nurture probably plays a mostly dominant role in these differences because their genetic (nature) variables are controlled.
(3) Overall Math Skills in Identical Twins: It is difficult to make precise judgments about the percentage contribution of nature/nurture for any individual's overall math skills, but it is known that both influences are present.
Methodologies for Studying Nature and Nurture
Comparative Genetic Studies: Scientists primarily study the influence of nature and nurture by comparing similarities between people who are genetically related versus those who are less genetically related.
Twin Studies:
Identical Twins (Monozygotic): Share 100\% of their genes, making them the most genetically related individuals possible.
Fraternal Twins (Dizygotic): Share approximately 50\% of their genes, similar to regular siblings, as they develop from two separate eggs fertilized by two separate sperm.
Key Finding: Identical twins exhibit more similarities across various psychological traits than fraternal twins, underscoring the significant influence of shared genes.
Application to Exam-Type Questions:
(1) Jack (boy) and Jane (girl) are twins: They must be fraternal twins, as identical twins are always of the same sex.
(2) Jack (boy) and John (boy) are twins: There is not enough information to determine if they are identical or fraternal, as fraternal twins can also be of the same sex.
The Influence of Nature: Temperament and Other Traits
Shared Psychological Features in Identical Twins: Even when raised apart, identical twins often share many psychological features, demonstrating nature's influence. These include:
Personality
Intelligence
Abilities
Interests and Fears
Brain Waves and Heart Rate
Temperament:
Definition: An individual's characteristic emotional reactivity or excitability, a fundamental part of our natural disposition, evident from infancy.
Identifiable Patterns in Infants: The book notes three patterns:
Easy Babies (most common): Predictable feeding and sleeping schedules, cheerful reactions to new situations.
Slow-to-Warm-Up Babies: Tend to resist or withdraw from new situations.
Difficult Babies: Characterized by irregular routines and irritability.
Genetic Basis: Temperament is strongly genetically based, with identical twins showing similar temperaments.
Long-Term Impact: Infantile temperament can predict later-life behaviors:
Shy 6-month-olds were more likely to be shy and socially anxious as teenagers.
Emotionally reactive 3-year-olds were more likely to be aggressive at age 21.
Nature and Nurture on Intelligence
Scientific Approach: Researchers examine intelligence similarities among individuals based on:
Shared Genes: To assess the influence of "nature."
Shared Environments: To assess the influence of "nurture," such as being raised in the same family or community.
Correlation of IQ Scores (Illustrative Patterns):
Influence of Nurture: A higher correlation of IQ scores for individuals reared together versus those reared apart (e.g., identical twins reared together vs. apart, or unrelated children reared together vs. apart) indicates the impact of a shared environment.
Influence of Nature: A higher correlation of IQ scores for more genetically related individuals versus less genetically related individuals (e.g., identical twins vs. nonidentical twins reared together) indicates the impact of shared genes.
Specific Examples from Chart Analysis:
Identical twins reared together show the highest IQ correlation ( +0.86), reflecting both strong genetic and environmental similarity.
Identical twins reared apart still show a high correlation ( +0.76), highlighting the strong genetic influence on intelligence even without shared environment.
Comparing Identical twins reared together to Nonidentical twins reared together (approx. +0.86 vs. +0.59) shows the significant role of genetic similarity.
Comparing Siblings reared together to Siblings reared apart (approx. +0.47 vs. +0.40) shows a modest environmental influence.
Unrelated children reared together show a correlation ( +0.32) due to shared environment, which drops to +0.01 when reared apart, demonstrating nurture's role.
Evolutionary Psychology
Foundational Role: Evolutionary theory is a cornerstone of biology, explaining the adaptive functions of animal features and behaviors, and their evolution.
Humans as Animals: Humans are also subject to evolutionary processes. Our brains and psychological tendencies developed based on what was adaptive for our ancestors' survival.
The Evolutionary Lag:
The human species evolved approximately 1.5 - 2.5 million years ago.
The modern world has changed drastically since then, creating a mismatch between our evolved predispositions and current societal demands.
Adaptive Behaviors vs. Modern Relevance:
Behaviors that were adaptive for survival in ancestral environments may be irrelevant or even harmful today.
Example: Aggression: Aggression might have been adaptive millions of years ago, providing access to resources or protection. However, in contemporary society, aggression typically leads to negative consequences such as jail or social rejection.
Conclusion: "We are, in some ways, biologically prepared for a world that no longer exists."
Evolutionary Psychology Applied: Attraction and Mate Selection
Key Assumptions about Sex Differences: Evolutionary psychology posits that men and women differ by evolutionary design.
These differences have evolved over time.
They are associated with distinct reproductive strategies aimed at passing on genes effectively.
Male Reproductive Strategy:
Minimal Investment: Men have historically had minimal biological investment in a single pregnancy, allowing for potentially many children with multiple partners.
Ensuring Reproductive Success: Evolutionary pressures led to preferences that maximized offspring quantity and certainty:
(1) Mating with a greater number of women.
(2) Prioritizing the fertility of mates (perceived through attractiveness and youth).
(3) Valuing chastity and sexual faithfulness to ensure paternity.
Female Reproductive Strategy:
Massive Investment: Women have a massive biological investment in pregnancy (typically one child per 9 months), requiring significant resources and protection.
Ensuring Reproductive Success: Evolutionary pressures led to preferences that maximized offspring survival and quality:
(1) Being highly selective in mate choice.
(2) Prioritizing a partner's ability to provide resources (money and status).
Casino Analogy for Differential Investment:
Men (many 1 chips): Like having 1000 extdollar1 chips, men might disperse their investment widely because the individual cost is low.
Women (one 1000 chip): Like having one 1 extdollar1000 chip, women are much more careful and selective about where they place their investment due to its high value.
Cross-Cultural Study on Mate Preferences (37 countries):
Findings replicated worldwide, suggesting an evolutionary basis:
Men: Consistently placed more importance on attractiveness and chastity.
Women: Consistently placed more importance on good earning potential and ambition.
Both Sexes: Valued kindness, intelligence, and good social skills equally.
Challenge to Socialization Argument: The consistent results across diverse cultures make a purely socialization-based argument difficult, reinforcing the idea of evolutionarily adaptive mate selection processes.
"Flashing Resources" Example (Cell Phone Study):
A study by the New York Times observed differences in cell phone behavior between men and women in public spaces.
Men were more likely to carry phones visibly and play with them, especially as the number of women in the bar increased, interpreted as a display of resources.
Exam-Type Question: Evolutionary theory primarily falls under the influence of nature when describing today's human thought and behavior, although it acknowledges the environment's role in triggering and shaping these evolved predispositions.
Learning Diary Reflection Prompt
Consider your similarities and differences from your parents and siblings in abilities, personality, and temperament. Research suggests that commonalities are often more attributable to shared genetics than shared family experiences or parenting styles.
Reflect on your reaction to this idea. How might this understanding influence your approach to parenting your own children, if at all? (e.g., emphasis on environment, acceptance of inherent traits, etc.)