Top 10 Replicated Findings From Behavioral Genetics
Plomin R, DeFries JC, Knopik VS, Neiderhiser JM · 2016
grade Creviewindependentreplicatednumbers spot-checked
Sample
synthesis; the load-bearing underlying studies include Kendler & Baker 2007 (55 genetic studies, 35 environmental measures) and Haworth 2010 (~11,000 twin pairs)
Population
Twin, adoption and GWAS samples across the behavioural-genetic literature.
Design
Perspectives on Psychological Science 11(1):3-23. A narrative synthesis, so graded C rather than B even though the designs it aggregates (twin, adoption, GWAS) are grade-B designs — the paper itself computes nothing new. Cited here for findings 5, 7, 8 and 9, which are the quantitative statement of this database's founding premise about the parenting literature.
Key findings
The two findings that matter most to a school builder are #7 and #8. #7: "most measures of the environment show significant genetic influence" — a review of 55 independent genetic studies found an AVERAGE HERITABILITY OF 0.27 across 35 diverse environmental measures (Kendler & Baker 2007). The things education research treats as inputs are themselves partly phenotypes. #8: "most associations between environmental measures and psychological traits are significantly mediated genetically" — e.g. two-thirds of the correlation between maternal negativity and adolescent antisocial behaviour is attributable to genetic factors. #5: heritability of intelligence rises from 41% at age 9 to 55% at 12 to 66% at 17 (Haworth 2010 — already held in this database, so not independent confirmation). #9: most environmental effects are NOT shared by children in the same family. Also: #1 all psychological traits show substantial genetic influence; #2 no trait is 100% heritable; #3 heritability is many genes of small effect; #6 age-to-age stability is mainly genetic; #10 "abnormal is normal" — common disorders are quantitative extremes.
Genetic confound
This paper IS the confound argument, stated as a replicated empirical regularity rather than an assumption. Its own caveat is important and this database keeps it: finding #2 is that NO trait is 100% heritable, and typical psychological-trait heritabilities are 30-50%, not 80-90%.
Effects
| Outcome | Metric | Value | Measure | Timing | Vs | Horizon | Class |
|---|---|---|---|---|---|---|---|
| Heritability of measures of "the environment" | mean h2 across 35 environmental measures | 0.27 (Kendler & Baker 2007, 55 genetic studies) | standardized | across ages | none | not-applicable | non-cognitive |
| Genetic mediation of an environment-outcome association | proportion of correlation genetically mediated | ~two-thirds (maternal negativity <-> adolescent antisocial behaviour) | standardized | adolescence | none | not-applicable | behaviour |
| Heritability of intelligence across development | h2 | 41% (age 9) -> 55% (age 12) -> 66% (age 17) | standardized | ages 9-17 | none | not-applicable | g |
| Typical heritability of psychological traits | h2 | substantial but never 100% — commonly 30-50% | standardized | across ages | none | not-applicable | non-cognitive |
Cited by
- The early home environment — what parents can and cannot causally movemixedconf: highgc: low
- The parent as instructor — what survives when the person teaching is the person who raised the childmixedconf: mediumgc: medium