Overview
This lecture explores the debate between nature (genetics) and nurture (environment) in shaping human traits, focusing on heritability, its limits, and complexity.
Nature vs. Nurture Debate
- Nature refers to genetic influences present before conception.
- Nurture refers to environmental factors after conception.
- John Locke emphasized nurture; Darwin stressed nature.
- Modern scientists believe traits result from an interplay between genes and environment.
Understanding Heritability
- Heritability measures how much trait differences in a group are due to genetics, ranging from 0 (all environment) to 1 (all genetics).
- It applies to populations, not individuals.
- High heritability doesn't mean a trait can't be changed by the environment.
Heritability Examples
- Group of white American males: average IQ 100, height 178 cm, 10% with spelling issues.
- Dyslexia has high heritability, meaning group differences are mostly genetic, but individual cases may be environmental.
- Height heritability is about 0.8 in well-nourished groups, drops to 0.5 in malnourished groups.
- Height is influenced more by environment when nutrition varies greatly.
- IQ heritability is about 0.6 in twenties and increases with age.
- Genetic differences explain around 60% of IQ variation in twenties, environment explains 40%.
Role of Randomness and Environment
- Environmental influences can be random, even among siblings raised together.
- Firstborns, on average, have higher IQs than younger siblings.
- Siblings raised together are only slightly more similar in IQ as adults than strangers.
- Parents and teachers have limited impact on a child's IQ.
The Crayfish Experiment
- Cloned crayfish with identical genes and environment developed differently in size, lifespan, and behavior.
- Suggests a complex interplay of nature, nurture, and possible random variation.
Key Terms & Definitions
- Nature — Genetic influences present before conception.
- Nurture — Environmental influences after conception.
- Heritability — A measure (0–1) of how much trait variation in a population is due to genetics.
- Dyslexia — A learning disorder affecting spelling, with high heritability.
Action Items / Next Steps
- Visit SproutsSchools.com for more resources and downloadable materials.
- Consider the role of both genetics and environment in future studies.