Top 10 Replicated Findings From Behavioral Genetics

modified 2018-11-02

In short:

10 findings from behavioral genetic research that have replicated robustly. These are “big” findings, both in terms of effect size and potential impact on psychological science

Results:

Finding 1. All psychological traits show significant and substantial genetic influence
Finding 2. No traits are 100% heritable
Finding 3. Heritability is caused by many genes of small effect
Finding 4. Phenotypic correlations between psychological traits show significant and substantial genetic mediation
Finding 5. The heritability of intelligence increases throughout development
Finding 6. Age-to-age stability is mainly due to genetics
Finding 7. Most measures of the “environment” show significant genetic influence
Finding 8. Most associations between environmental measures and psychological traits are significantly mediated genetically
Finding 9. Most environmental effects are not shared by children growing up in the same family
Finding 10. Abnormal is normal

Questions raised:

More details on correlations between heritable traits (height/intelligence? Altruism/intelligence? Height/altruism??)

Insights, lessons learnt:

Genetics is has a huge impact on every aspect of a person. Environment still has an effect, but less than might be intuitive. In some cases genetics influences the environment itself.
Subjects that are contreversial might do stronger studies, out of necessity
Disorders and traits are not binary things, but very much a point on a scale (lots of genes coding for each trait, and traits covariant since they rely on the same traits)

Highlights:

A recent concern in psychological science is that many statistically significant findings, including some classic findings, do not replicate

Finding 1. All psychological traits show significant and substantial genetic influence

resemblance is compared in pairs of identical and fraternal twins: cognitive abilities and disabilities, psychopathology, personality, substance use and abuse, and health psychology. Traits in these domains have consistently shown significant genetic influence in adequately powered studies

Traits such as political beliefs, religiosity, altruism, and food preferences also have shown significant genetic influence (Plomin et聽 al., 2013).

A recent meta-analysis of data drawn from 3,000 publications on nearly 18,000 traits of 15 million twin pairs showed that this finding is not limited to psychological traits

for general intelligence, heritability estimates are typically about 50% [鈥 with 95% confidence intervals on the order of between 45% and 55%.

For personality, heritability estimates are usually between 30% and 50%

The challenge now is to find any reliably measured behavioral trait for which genetic influence is not significantly different from zero in more than one adequately powered study.

Finding 2. No traits are 100% heritable

some traits, such as individual differences in height, yield heritability as high as 90%.

Although this finding might seem obvious and unsurprising, it is crucial because it provides the strongest available evidence for the importance of environmental influence after controlling for genetic influence. Because genetic influence is significant and substantial, one must control for genetic influence when investigating environmental influence.

Finding 3. Heritability is caused by many genes of small effect

Powerful but overlooked evidence that many genes affect complex traits including behavior comes from selection studies in nonhuman animal research. If only a few genes were responsible for the heritability of a trait, selected lines would separate after a few generations and would not diverge any further in later generations. In contrast, selection studies of complex traits show a linear response to selection even after dozens of generations of selection

Finding 4. Phenotypic correlations between psychological traits show significant and substantial genetic mediation

ie, the reason some traits seem to be correlated (for example depression and anxiety, language and maths skills, etc.) is that they are acted upon by similar genes.

a recent review of molecular genetic studies of schizophrenia concluded that “[t]here is evidence for shared genetic risk between schizophrenia, bipolar disorder, autism spectrum disorders, intellectual disability and attention-deficit and hyperactivity disorder

Finding 5. The heritability of intelligence increases throughout development

an analysis of cross-sectional data for 11,000 pairs of twins-larger than all previous twin studies combined-showed that the heritability of intelligence increases significantly from 41% in childhood (age 9) to 55% in adolescence (age 12) and to 66% in young adulthood (age 17; Haworth et聽al., 2010)

same as the observation (rationally speaking podcast) that while parent behaviour can influence IQ in the short term, in the long term people revert so a genetic baseline (around the age of 30). This was also believed to be the case for most other traits by the author of the book who was being interviewed

Increasing heritability for intelligence is interesting because other domains such as personality do not show systematic changes in heritability during development

this looks to be contested!

Finding 6. Age-to-age stability is mainly due to genetics

In other words, genetic effects contribute to continuity (the same genes affect the trait across age), whereas age-to-age change is primarily the provenance of environmental factors

how can the same genes largely affect intelligence across the life course and yet account for more variance as time goes by? Increasing heritability despite genetic stability implies some contribution from what has been called genetic amplification (Plomin & DeFries, 1985). In other words, genetic nudges early in development are magnified as time goes by, increasing heritability, but the same genetic propensities continue to affect behavior throughout the life course

Finding 7. Most measures of the “environment” show significant genetic influence

How can measures of the environment show genetic influence? The reason appears to be that such measures do not assess the environment independent of the person. As noted earlier, humans select, modify, and create environments correlated with their genetic behavioral propensities such as personality and psychopathology
For example, in studies of twin children, parenting has been found to reflect genetic differences in children’s characteristics

Shikishima, Hiraishi, Yamagata, Neiderhiser, and Ando (2012) compared parenting in Japan and Sweden and found that parenting in Japan showed more genetic influence than in Sweden, consistent with the view that parenting is more child centered in Japan than in the West.

Finding 8. Most associations between environmental measures and psychological traits are significantly mediated genetically

For example, rather than assuming that correlations between parenting and children’s behavior are caused by the environmental effect of parenting on children’s behavior, one should consider the possibility that the correlation is in part due to genetic factors that influence both parenting and children’s behavior

the first study of this type (conducted by Pike, McGuire, Hetherington, Reiss, & Plomin, 1996) indicated that two thirds of the correlation between maternal negativity and adolescent children’s antisocial behavior could be attributed to genetic factors. More than 100 studies have reported similar results.

It suggests a general way of thinking about how genotypes develop into phenotypes, from a passive model of imposed environments to an active model of shaped experiences in which humans select, modify, and create experiences in part based on their genetic propensities.

Finding 9. Most environmental effects are not shared by children growing up in the same family

for most behavioral dimensions and disorders, it is genetics that accounts for similarity among siblings. Although environmental effects have a major impact (see Finding 2), the salient environmental influences do not make siblings growing up in the same family similar.

environment DOES make a difference, but not as much as genetics.

An interesting developmental exception is that shared environmental influence is found for intelligence up until adolescence and then diminishes as adolescents begin to make their own way in the world, as shown in meta-analyses (Briley & Tucker-Drob, 2013; Haworth et聽al., 2010)

this is the result I was thinking of probably

It is important to reiterate that the message is not that family experiences are unimportant but rather that the salient experiences that affect children’s development are specific to each child in the family, not general to all children in the family

but are largely genetic, so whatever you do it might not make a huge difference鈥?the conclusion of the author I mentioned above is useful here:
A) if you and the child are having fun, you are winning. It doesn’t matter if you cannot make them smarter in a significant long-term way
B) Short term is important too! Discipline when they are 5 will make your and others life better, even if it will wear off when they are 12

Finding 10. Abnormal is normal

autism, and hyperactivity. Quantitative genetic methods suggest that common disorders are the extremes of the same genetic factors responsible for heritability throughout the distribution, although the evidence is indirect and the methods are somewhat abstruse.

so we are all on a scale, a disorder is when someone is near one end, it is not a binary thing.

We suggest that the controversy and conflict surrounding behavioral genetics had the positive effect of motivating bigger and better studies that met the high standard of evidence needed to convince skeptical psychological scientists of the importance of genetics in the development of individual differences in behavior. A single study was not enough-it was the convergence of evidence across studies using different methods that tipped the balance of opinion. The relevance for other embattled fields is the comfort of knowing that the extra effort required to address skepticism and criticism can pay off in building a stronger foundation for a field.

also effect sizes (30-50%) are large, which tends to correlate with reproducibility