The heritability of political beliefs is unintuitive. They’re clearly not “genetic” (Nick Land’s genes don’t contain a copy of Xenosystems), but they are heritable because there are heritable traits (e.g. height, intelligence, personality) cause people to adopt different political beliefs.
It makes sense. I could imagine even small aspects of personality such as disgust sensitivity influencing political views. I think I must have confused this 10% heritability with something else.
Anyways, a decently high heritability of political views means that the claims that the culture is going to become more rightwing due to the widening birth rate difference between the left and the right are not absurd.
I've seen twin studies under attack. I used to think that twin studies were uncontroversially the gold standard of heritability research. Would you point to any article in particular as a counter-argument to these criticisms?
Here's a summary of why genetic (heritable, chromsomal) factors in fluid intelligence and poverty tend to be over-estimated in MZ/DZ studies:
1. "Equal Environment Assumption" is often violated
2. Genes and environment can interact or correlate in complex ways. For example, a child’s genetic traits may shape their environment (evocative genetic influence), or children may seek out environments that fit their genetic predispositions (active genetic influence). These dynamics mean that MZ twins may experience even more similar environments than DZ twins, further biasing heritability estimates upward.
3. Neglect of Prenatal and Early-Life Environmental Factors
Twin studies often do not adequately account for critical prenatal and early-life factors—such as maternal nutrition, exposure to toxins (lead, mycotoxins, indoor smoke), maternal anaemia, and malnutrition—that can have lasting impacts on cognitive development and health. These factors can create similarities or differences between twins that are wrongly attributed to genetics if not properly controlled.
For example, MZ twins share a placenta more often than DZ twins, which can lead to more similar prenatal environments for MZ pairs, further confounding the distinction between genetic and environmental effects.
4. Sampling and Generalizability Issues
Twins, especially those who participate in studies, may not be representative of the general population, potentially limiting the generalizability of findings. Selection biases (e.g., volunteerism, socioeconomic status) can further skew results.
5. Assumptions About Genetic Sharing
While MZ twins are assumed to share 100% of their genes, post-zygotic mutations can introduce genetic differences even between identical twins, leading to overestimation of heritability.
6. Assortative Mating
If parents are more similar to each other than random (assortative mating), DZ twins may share more than 50% of relevant genes, which can lead to underestimation of shared environmental effects and overestimation of genetic effects.
7. Inability to Identify Specific Causes
Twin studies can estimate the proportion of variance due to genetic and environmental factors but cannot identify which specific genes or environmental exposures are responsible for observed differences.
Don't want to be that guy, but [citation needed]. It's probably invalid for BMI but MZT correlations are usually easy to explain with genes + twin-specific effects + shared environments.
>Genes and environment can interact
Interactions are less common than main effects, so apriori interactionism should not be reason to shun hereditarianism.
Representative samples of twins (e.g. Scottish IQ twin study) find the same results as other studies, and sampling can theoretically restrict both genetic and environmental variance; it's presence doesn't invalidate heritability estimates.
>If parents are more similar to each other than random (assortative mating), DZ twins may share more than 50% of relevant genes, which can lead to underestimation of shared environmental effects and overestimation of genetic effects.
The exact opposite is true. Do the maths.
>While MZ twins are assumed to share 100% of their genes, post-zygotic mutations can introduce genetic differences even between identical twins, leading to overestimation of heritability.
If the effect is shared between siblings/twins, then it's allocated to the shared environmental component. Otherwise, it's allocated to the unshared environmental component.
Great analysis!
The heritability of political views one was surprising. I vaguely remember studies saying it was only like 10%
The heritability of political beliefs is unintuitive. They’re clearly not “genetic” (Nick Land’s genes don’t contain a copy of Xenosystems), but they are heritable because there are heritable traits (e.g. height, intelligence, personality) cause people to adopt different political beliefs.
It makes sense. I could imagine even small aspects of personality such as disgust sensitivity influencing political views. I think I must have confused this 10% heritability with something else.
Anyways, a decently high heritability of political views means that the claims that the culture is going to become more rightwing due to the widening birth rate difference between the left and the right are not absurd.
I've seen twin studies under attack. I used to think that twin studies were uncontroversially the gold standard of heritability research. Would you point to any article in particular as a counter-argument to these criticisms?
I'm writing it.
Could you please do the same for mental disorders?
Here's a summary of why genetic (heritable, chromsomal) factors in fluid intelligence and poverty tend to be over-estimated in MZ/DZ studies:
1. "Equal Environment Assumption" is often violated
2. Genes and environment can interact or correlate in complex ways. For example, a child’s genetic traits may shape their environment (evocative genetic influence), or children may seek out environments that fit their genetic predispositions (active genetic influence). These dynamics mean that MZ twins may experience even more similar environments than DZ twins, further biasing heritability estimates upward.
3. Neglect of Prenatal and Early-Life Environmental Factors
Twin studies often do not adequately account for critical prenatal and early-life factors—such as maternal nutrition, exposure to toxins (lead, mycotoxins, indoor smoke), maternal anaemia, and malnutrition—that can have lasting impacts on cognitive development and health. These factors can create similarities or differences between twins that are wrongly attributed to genetics if not properly controlled.
For example, MZ twins share a placenta more often than DZ twins, which can lead to more similar prenatal environments for MZ pairs, further confounding the distinction between genetic and environmental effects.
4. Sampling and Generalizability Issues
Twins, especially those who participate in studies, may not be representative of the general population, potentially limiting the generalizability of findings. Selection biases (e.g., volunteerism, socioeconomic status) can further skew results.
5. Assumptions About Genetic Sharing
While MZ twins are assumed to share 100% of their genes, post-zygotic mutations can introduce genetic differences even between identical twins, leading to overestimation of heritability.
6. Assortative Mating
If parents are more similar to each other than random (assortative mating), DZ twins may share more than 50% of relevant genes, which can lead to underestimation of shared environmental effects and overestimation of genetic effects.
7. Inability to Identify Specific Causes
Twin studies can estimate the proportion of variance due to genetic and environmental factors but cannot identify which specific genes or environmental exposures are responsible for observed differences.
Sources:
https://www.perplexity.ai/search/challenge-the-conclusions-of-t-dvxJbQPzTriNV38T7hjxcg
>"Equal Environment Assumption" is often violated
Don't want to be that guy, but [citation needed]. It's probably invalid for BMI but MZT correlations are usually easy to explain with genes + twin-specific effects + shared environments.
>Genes and environment can interact
Interactions are less common than main effects, so apriori interactionism should not be reason to shun hereditarianism.
https://rpubs.com/Jonatan/interactions
>Sampling and Generalizability Issues
Representative samples of twins (e.g. Scottish IQ twin study) find the same results as other studies, and sampling can theoretically restrict both genetic and environmental variance; it's presence doesn't invalidate heritability estimates.
>If parents are more similar to each other than random (assortative mating), DZ twins may share more than 50% of relevant genes, which can lead to underestimation of shared environmental effects and overestimation of genetic effects.
The exact opposite is true. Do the maths.
>While MZ twins are assumed to share 100% of their genes, post-zygotic mutations can introduce genetic differences even between identical twins, leading to overestimation of heritability.
The exact opposite is true, again. Maths please.
>Inability to Identify Specific Causes
Doesn't matter.
For most traits, EEA is not "often violated":
https://menghu.substack.com/p/sometimes-biased-but-not-systematically
Regarding assortative mating, you have it completely backwards, it's the other way around. It leads to *under*estimates of heritability.
There may be some interactions and correlations, but not very relevant to real-world implications.
Does this take into account epigenetic and congenital factors (like folate, smoke, mycotoxins, anemia, fever in early pregnancy)?
>Epigenetic
Isn't epigenetic variance technically genetic?
>Congenital factors
If the effect is shared between siblings/twins, then it's allocated to the shared environmental component. Otherwise, it's allocated to the unshared environmental component.
Amazing