Heritability Insights from Twin Studies

Below is a summary of several trait domains in which classical twin‐study designs have consistently found that genetic factors (“nature”) account for more variance than shared environmental factors (“nurture”). For each trait, approximate heritability estimates (h²) and key references are provided.

Overview of Twin‐Study Heritability
Classical twin studies compare similarity (usually via intraclass correlations) between monozygotic (MZ) twins (who share essentially 100% of segregating alleles) and dizygotic (DZ) twins (who share, on average, 50% of segregating alleles). When MZ correlations exceed DZ correlations substantially, this is taken as evidence for additive genetic effects. Modern meta‐analyses of twin data across thousands of traits confirm that nearly every measurable trait shows at least moderate genetic influence, often surpassing shared‐environmental contributions. en.wikipedia.orgwww.researchgate.net

1. Physical and Anthropometric Traits

Height

• Heritability (h²) in adolescence and adulthood: ~0.70–0.90.
• Developmental pattern: Heritability is lower (0.20–0.50) in infancy and early childhood, then steadily rises to ~0.70–0.90 by adolescence/adulthood. www.nature.comwww.scientificamerican.com

Example: Finnish twin data show h² ≈ 0.78 in adult men and ≈ 0.75 in adult women. www.scientificamerican.com

Body Mass Index (BMI) and Obesity

• Heritability (h²): varies by age; roughly 0.40–0.75 in children and adults.

• Children: h² ≈ 0.80–0.90

• Adults: h² ≈ 0.40–0.70 (declining slightly with age)

• Meta‐analysis findings: Over 140,000 twin pairs yield a mean h² ~ 0.70 for BMI after infancy, with somewhat higher estimates in childhood and modest decreases in later adulthood. pmc.ncbi.nlm.nih.govwww.researchgate.net

Differences across studies partly reflect methodological factors (e.g., AE vs. ACE models, measured vs. self‐reported BMI). pmc.ncbi.nlm.nih.gov

2. Cognitive and Personality Traits

General Intelligence (IQ)

• Heritability (h²):

• Childhood: ~0.20–0.50 (rising with age)

• Adolescence/adulthood: ~0.60–0.80 (some studies report up to ~0.85 by late adolescence)

• Key observations: Heritability of IQ increases across development (the “Wilson effect”), with shared‐environmental contributions waning after early childhood. en.wikipedia.orgen.wikipedia.org

For adults, most twin studies report h² between 0.70 and 0.80; one large Swedish study found h² ≈ 0.80 for general cognitive ability. en.wikipedia.org

Specific Cognitive Subdomains (e.g., Spatial Ability)

• Spatial ability: h² ≈ 0.69 in young adults; shared environment accounts for ≈ 8% of variance. en.wikipedia.org

Personality (Big Five Dimensions)

• Heritability (h²):

• Openness: ~0.57

• Extraversion: ~0.54

• Conscientiousness: ~0.49

• Neuroticism: ~0.48

• Agreeableness: ~0.42

• Notes: Roughly 40–60% of variance in each of the Big Five dimensions is attributable to genetic factors, with the remainder mostly due to non‐shared environment. en.wikipedia.orgpmc.ncbi.nlm.nih.gov

A 1996 study of twins reported those percentages, and subsequent work (e.g., meta‐analyses through 2003) confirm similar magnitudes across cultures. en.wikipedia.org

3. Psychiatric and Behavioral Disorders

Autism Spectrum Disorder (ASD)

• Heritability (h²): ~0.80–0.90 (twin studies from 1977–1995 suggest > 0.90).
• Summary: Concordance rates among MZ twins approach ~90%, whereas DZ concordance rates are much lower. Genetic factors thus account for ∼80–90% of liability; non‐shared environmental factors account for most of the remaining variance. en.wikipedia.orgen.wikipedia.org

High heritability does not imply deterministic inheritance; rare de novo mutations and environmental modifiers also play roles. en.wikipedia.org

Schizophrenia

• Heritability (h²): ~0.60–0.85 (most large twin‐study meta‐analyses converge around ~0.80).
• Twin concordance: MZ concordance ≈ 15–28%, DZ ≈ 6%; estimates translate to population‐level h² ~ 0.80. www.sciencedirect.comwww.psychiatrymargins.com

One major Swedish twin study affirmed h² ≈ 0.80, with no significant contribution from shared environment. www.sciencedirect.com

Major Depressive Disorder (MDD)

• Heritability (h²): ~0.35–0.50
• Sex differences: Some twin samples show h² ≈ 0.42 for women and ≈ 0.29 for men; overall meta‐analytic h² ≈ 0.37 (95% CI = 0.31–0.42). pmc.ncbi.nlm.nih.govpubmed.ncbi.nlm.nih.gov

Shared‐environmental influences are negligible; non‐shared environment (including measurement error) accounts for the majority of residual variance. pmc.ncbi.nlm.nih.gov

Attention‐Deficit/Hyperactivity Disorder (ADHD)

• Heritability (h²): ~0.60–0.90 (mean across 37 twin studies ≈ 0.74; categorical diagnoses often ∼0.80). www.nature.compmc.ncbi.nlm.nih.gov

Some adult twin studies (self‐reported ADHD traits) yield lower estimates (~0.30–0.40), but childhood/adolescent twins consistently show h² ≈ 0.70–0.80. pmc.ncbi.nlm.nih.gov

4. Other Commonly Studied Traits

Major Anxiety Disorders

• Heritability (h²): ~0.30–0.50 (comparable to depression; meta‐analyses report twin‐h² ≈ 0.30–0.50). www.nature.com

Genetic overlap with depression is substantial, but unique genetic factors also contribute.

Substance Use and Dependence (e.g., Alcoholism)

• Heritability (h²): ~0.50–0.70 for alcohol dependence; twin concordance: MZ ≈ 50–70%, DZ ≈ 30–40%.
• References: Numerous twin studies converge on h² ~ 0.50–0.60; see meta‐analyses in psychiatric genetics literature (e.g., Kendler et al. reviews). www.sciencedirect.compmc.ncbi.nlm.nih.gov

Shared environment typically plays a minor role once early adulthood is reached; non‐shared environmental factors drive residual risk.

5. Summary Table of Select Heritability Estimates

Key Takeaways

• Genetic influence predominates for most quantitative and diagnostic traits once twin‐study analyses control for shared environment.
• Heritability estimates are population‐ and age‐specific (e.g., IQ heritability rises from ~0.20 in early childhood to ~0.80 in adulthood; BMI heritability is higher in childhood than later adulthood).
• Shared environmental effects (e.g., family socioeconomic status, parenting style) often account for a relatively small fraction of variance, especially after early childhood—non‐shared environment (unique experiences, measurement error) typically explains the remaining variance.
• Even traits with very high heritability (e.g., autism, schizophrenia) do not imply determinism; environmental triggers, epigenetic mechanisms, and gene–environment interplay remain critical in overall trait expression.

References

• General Twin‐Study Reviews

• Visscher, P. M., et al. “Meta‐analysis of the heritability of human traits based on fifty years of twin studies.” Nat. Genet. 49, 591–600 (2017). www.researchgate.net

• Polderman, T. J. C., et al. “Meta‐analysis of the heritability of human traits based on fifty years of twin studies.” Nat. Genet. 47, 702–709 (2015). www.researchgate.net

• Physical Traits

• Silventoinen, K., et al. “Genetic and environmental influences on body mass index from infancy to adulthood.” Sci Rep 6, 28496 (2016). www.nature.com

• Elks, C. E., et al. “Variability in the heritability of body mass index: a systematic review and meta‐regression.” Front. Genet. 3, 29 (2012). pmc.ncbi.nlm.nih.gov

• Cognitive Traits

• Plomin, R., et al. “Heritability of cognitive abilities: literature review.” Behav Genet 40, 801–812 (2010). en.wikipedia.orgen.wikipedia.org

• Turkheimer, E., et al. “Socioeconomic status modifies heritability of IQ in young children.” Psychol Sci 14, 623–628 (2003). en.wikipedia.org

• Personality

• Jang, K. L., Livesley, W. J., Vernon, P. A. “Heritability of the Big Five Personality dimensions and their facets: a twin study.” J Pers 64, 577–591 (1996). en.wikipedia.orgpmc.ncbi.nlm.nih.gov

• Psychiatric Disorders

• Bouchard, T. J., et al. “Sources of human psychological differences: the Minnesota Study of Twins Reared Apart.” Science 250, 223–228 (1990). en.wikipedia.org

• Hilker, R., et al. “Heritability of schizophrenia and schizophrenia spectrum based on the nationwide Danish Twin Register.” Biol Psychiatry 83, 492–498 (2018). www.sciencedirect.com

• Kendler, K. S., et al. “A Swedish national twin study of lifetime major depression.” Am J Psychiatry 163, 109–114 (2006). pubmed.ncbi.nlm.nih.gov

• Faraone, S. V., Larsson, H. “Genetics of attention deficit hyperactivity disorder.” Mol Psychiatry 24, 562–575 (2019). www.nature.com For further detail, the above‐cited sources and comprehensive twin‐study meta-databases (e.g., the MaTCH webtool) can be consulted.