When you start off an article with a pop-science fallacy, it can color the rest of the article in a negative light:
> "...and mutational load affects both facial symmetry and mental illness."
There's little solid evidence for inherited mental illness, not excluding severe neuro-developmental abnormalities (which may also have environmental causes such as teratogen exposure), in fact there aren't even any solid independent physical-chemical tests for DSM disorders.
> (8) Family genetic studies. The phrase “family genetic studies” is commonly used in psychiatry to refer to designs in which investigators examine the familial aggregation of one or more disorders, such as panic disorder or major depression, within intact (i.e., non-adoptive) families (e.g., Weissman, 1993). Given that the familial aggregation of one or more disorders within intact families could be due to shared environment rather than—or in addition to—shared genes (Smoller and Finn, 2003), the phrase “family genetic study” is misleading. This term implies erroneously that familial clustering of a disorder is necessarily more likely to be genetic than environmental. It may also imply incorrectly (Kendler and Neale, 2009) that studies of intact families permit investigators to disentangle the effects of shared genes from shared environment. Twin or adoption studies are necessary to accomplish this goal.
> (9) Genetically determined Few if any psychological capacities are genetically “determined”; at most, they are genetically influenced. Even schizophrenia, which is among the most heritable of all mental disorders, appears to have a heritability of between 70 and 90% as estimated by twin designs (Mulle, 2012), leaving room for still undetermined environmental influences. Moreover, data strongly suggest that schizophrenia and most other major mental disorders are highly polygenic. In addition, the heritability of most adult personality traits, such as neuroticism and extraversion, appears to be between 30 and 60% (Kandler, 2012). This finding again points to a potent role for environmental influences.
> There's little solid evidence for inherited mental illness
> Even schizophrenia, which is among the most heritable of all mental disorders, appears to have a heritability of between 70 and 90% as estimated by twin designs (Mulle, 2012), leaving room for still undetermined environmental influences.
You can think of those percentages less like “there is only 10-30% left to explain” and more like “we can explain most of it we think but we have no idea how these complex factors interact”
They basically look at fraternal and identical twins and assume (because their environments are otherwise probably close) that any differences in outcome are heritable. It’s a huge leap of faith.
> They basically look at fraternal and identical twins and assume (because their environments are otherwise probably close) that any differences in outcome are heritable. It’s a huge leap of faith.
You’re making it sound like the researchers are idiots who have never thought about how their tools might not be measuring what they hope they are.
As well as identical/fraternal twins you can also look at other sorts of relatedness, e.g. half siblings are on average as related as first cousins and on average you’re as closely related to each parent as each full sibling. Psychological traits are inherited like height is, not like language is[1]. Mental illness is highly heritable though the expression varies[2].
As a parallel line of evidence to confirm classical twin studies and those based on degrees of shared ancestry cheap genetic testing has allowed testing how closely people are related. So you don’t have to assume a sibling shares 50% of their genes. You can see if they’re 73% similar or 41%. Or you can take people who have no known shared recent ancestry and see how similar they are on the trait of interest.
To the best of my knowledge behaviour genetics is holding up. For psychological traits genetics is more powerful than developmental noise.
[1]> Genetic Influence on Human
Psychological Traits
> There is now a large body of evidence that supports the conclusion that individual differences in most, if not all, reliably measured psychological traits, normal and abnormal, are substantively influenced by genetic factors. This fact has important implications for research and theory building in psychology, as evidence of genetic influence unleashes a cascade of questions regarding the sources of variance in such traits. A brief list of those questions is provided, and representative findings regarding genetic and environmental influences are presented for the domains of personality, intelligence, psycho- logical interests, psychiatric illnesses, and social attitudes. These findings are consistent with those reported for the traits of other species and for many human physical traits, suggesting that they may represent a general biological phenomenon.
[2]> The p factor: genetic analyses support a general dimension of psychopathology in childhood and adolescence
> Diverse forms of psychopathology generally load on a common p factor, which is highly heritable. There are substantial genetic influences on the stability of p across childhood. Our analyses indicate genetic overlap between general risk for psychiatric disorders in adulthood and p in childhood, even as young as age 7.
Depending on the twin study yes you can go into all kinds of sibling groups/measures too. However mapping it to something that must have had evolutionary pressure on it in ways we still don’t clearly understand is not at all straightforward, so yes, in a sense, I think most psychologists, who have no evolutionary training, are doing this very wrong.
You’re basically saying “some limits of cognition are heritable” which is so obvious as to be inarguable.
The huge qualifier in what you quoted is “reliably measured psychological traits.” They also have to be defined within psychological language and linked to genetics through behavior or biological indicators. There are exceedingly few of these, and schizophrenia, autism, etc, are not them.
Psychology as a whole without evolutionary considerations to articulate on is free-floating.
There is a long history of psychologists justifying their approach, but the reality is that reproducibility in psychology is still at something like 35%.
Edit to say the second paper is interesting, but it seems to me to have a number of flaws.
If I understand this right, GWAS are capturing everything from the genome.
This includes any genetic determination of appearance, food preferences, etc.
Then the sample is only healthy twins from narrow genetic/cultural stock: England/Wales born over two years in the 90s.
This means that in addition to sweeping up genetic factors associated with brain development, you are capturing all visible/inherent-behavioral inputs to a multi-stage developmental process that includes interactions with technology, other people, school systems, etc.
Of course you can explain a majority of the outcome. It won’t replicate though, because it is dependent on that narrow time slice of culture, nutrition, parenting practices, technology, etc.
If this study replicates in Asia, South America, or Africa, with similar genetic components in the PCA, I’ll admit I’m wrong.
Heck if it even replicates in England with twins from the 1960s I’ll admit I’m wrong.
Is it "mental illness" or is it acting out?
Is it brain issues or behavioral issues that are the problem?
We have known for millennia that original sin is carried and transmitted by everyone in the human race. John Bradshaw posited the thesis that shame is carried in families, across generations. We all know that cycles of abuse happen again and again, passed father to son, mother to daughter, uncle to niece.
Psychiatrists flail about and disclaim any knowledge about the genesis of "mental illness". But we know the causes. The causes are preventable, but sometimes the cost of prevention is everything we hold dear.
> "...and mutational load affects both facial symmetry and mental illness."
There's little solid evidence for inherited mental illness, not excluding severe neuro-developmental abnormalities (which may also have environmental causes such as teratogen exposure), in fact there aren't even any solid independent physical-chemical tests for DSM disorders.