[lynx97]

(How) did they control for parental influence vs. genetic heritability? I grew up with a pathologically anxious mother. I still remember having to counteract her behaviour to avoid it leaking into my world, before I managed to move out. She is still a trigger for me, 30 years later. I can only stand having her around me for at max. 2 hours, then my vessel is full. IMO, I am not convinced that a sibling study rules out environmental influences.

[andoando]

They had a control for adoptive siblings. The critic in me says, ok what was their age of adoption, do parents perhaps treat adopted children differently, do adopted children perhaps grow behaviors unindicative of ADHD, does the knowledge that its genetic influence the diagnoses themself?

[lynx97]

The age of adoption seems crucial to rule out early childhood trauma induced by the parents. I actually know mine, although it took me 35 years to get my mother to admit what happened. My point, I am very skeptical when it comes to parents reflecting on the bad influences they might have had on the development of their child. After all, bad parenting has a pretty harsh stigma in society (and it should!)

[rusk]

Yes but if the SAME behaviour emerges regardless of parenting style then that is significant

[verteu]

The twin studies would largely control for that.

[rendx]

"twin studies fail to separate the effects of genes and the prenatal environment. This failure casts doubt on claims of the relative effects of genes and environment on intelligence, psychiatric disorders, personality and other psychological variables, and other conditions."

https://www.psychologytoday.com/gb/blog/looking-in-the-cultu...

"Although many twin studies have been conducted (which is quite an understatement; there are almost 9,000 hits for “twin study” on PubMed!), there have long been critics who argue that they are scientifically worthless."

Smith, Jinkinson. (2020). The debate over twin studies: an overview. http://dx.doi.org/10.22541/au.159674847.78026661

"Because heritability is defined by both genetic and environmental influences, it is not a fixed characteristic of a disease or trait, but a population-specific estimate, analogous to, for example, the mean height, cholesterol level or life expectancy in a population. It also cannot be interpretated at the family or individual level."

Kaprio J. (2012). Twins and the mystery of missing heritability: the contribution of gene-environment interactions. Journal of internal medicine, 272(5), 440–448. https://doi.org/10.1111/j.1365-2796.2012.02587.x

[lynx97]

Ahem, sorry for being slow and/or stupid, but how? Aren't both twins exposed to the same parental style?

[jrapdx3]

In studies of monozygotic twins (shared genetic predisposition), typically the twins were raised in different environments (adoption, etc.). If behavior among the twins is divergent then environmental factors are likely predominant. OTOH if concordance of traits is strongly evident, behavior is attributable to genetic factors.

[doright]

My understanding is that separating children from their biological parents has wide-reaching consequences, even if done in a non-traumatic way, and even if they are ultimately raised by a different set of parents. I would imagine the trauma originating from having to be adopted could be a uniquely triggering factor for genetic predisposition in the case of only one of the twins. How would twin studies be able to account for that?

[rendx]

I agree. Also, the prenatal environment (9 months of development!) and circumstances of birth, which both twins share, is not accounted for at all. Or rather, it is accounted for as "heritability" by twin studies, which is plainly wrong.

https://williamjbarry.substack.com/p/the-first-1000-days

[verteu]

No need for family separation. You simply compare the correlation between monozygotic ("identical") twins vs dizygotic ("non-identical") twins.

For example, monozygotic twins will always have the same eye color (99+% correlation), while dizygotic twins do not. Thus we can conclude eye color is genetic. Both twins are raised by their respective parents, so it's unlikely parenting is causing this difference in eye-color-correlation.

[rusk]

Not if they’re raised in different families.