Adoption studies are biased toward the null of no parenting effect, because adoptive parents aren’t randomly selected from the population of potential parents (they often are screened to be similar to biological parents).
Twin studies I think are particularly flawed when it comes to estimating heritability (a term that has an incoherent definition). Twins have a shared pre-natal environment. In some cases, they even share a placenta.
Plus, the whole gene vs. environment discussion is obsolete, in light of the findings of the past decade. Everything is gene-environment interaction.
So most of what you have written makes sense but there are some major issues with some parts.
heritability (a term that has an incoherent definition)
Can you expand on what you think about the definition is incoherent? This is a pretty standard term.
the whole gene vs. environment discussion is obsolete, in light of the findings of the past decade. Everything is gene-environment interaction.
The fact that many genes interact in a complicated way with the environment is not newly discovered. It doesn’t change the fact that in some contexts genes or environment can matter more or less. For example, if one has a gene that codes for some form of mental retardation, in most cases, environment can’t change that. (I say in most cases because there are a few exceptions especially related to issues related to trace nutrients or to bad reactions to specific compounds). Similarly, if someone has severe lead poisoning they are going to have pretty bad problems regardless of what the genes the person has.
The first two points you made while roughly valid connect to a more general issue- yes these studies have flaws, but just because a technique has flaws doesn’t mean we can’t use it to learn (especially when in this context the issues you bring up are well known to the researchers).
The answer to the question “what proportion of phenotypic variability is due to genetic variability?” always has the same answer: “it depends!” What population of environments are you doing this calculation over? A trait can go from close to 0% heritable to close to 100% heritable, depending on the range of environments in the sample. That’s a definition problem. Further, what should we count as ‘genetic’? Gene expression can depend on the environment of the parents, for example (DNA methylation, etc). That’s an environmental inheritance. I just think there is an old way of talking about these things that needs to go away in light of current knowledge.
I agree with you that we still can learn a lot from these studies.
The definition of ‘heritable’ being underspecified (since you have to specify what population of environments you’re considering) is not the same as being incoherent.
Adoption studies are biased toward the null of no parenting effect, because adoptive parents aren’t randomly selected from the population of potential parents (they often are screened to be similar to biological parents).
Twin studies I think are particularly flawed when it comes to estimating heritability (a term that has an incoherent definition). Twins have a shared pre-natal environment. In some cases, they even share a placenta.
Plus, the whole gene vs. environment discussion is obsolete, in light of the findings of the past decade. Everything is gene-environment interaction.
So most of what you have written makes sense but there are some major issues with some parts.
Can you expand on what you think about the definition is incoherent? This is a pretty standard term.
The fact that many genes interact in a complicated way with the environment is not newly discovered. It doesn’t change the fact that in some contexts genes or environment can matter more or less. For example, if one has a gene that codes for some form of mental retardation, in most cases, environment can’t change that. (I say in most cases because there are a few exceptions especially related to issues related to trace nutrients or to bad reactions to specific compounds). Similarly, if someone has severe lead poisoning they are going to have pretty bad problems regardless of what the genes the person has.
The first two points you made while roughly valid connect to a more general issue- yes these studies have flaws, but just because a technique has flaws doesn’t mean we can’t use it to learn (especially when in this context the issues you bring up are well known to the researchers).
The answer to the question “what proportion of phenotypic variability is due to genetic variability?” always has the same answer: “it depends!” What population of environments are you doing this calculation over? A trait can go from close to 0% heritable to close to 100% heritable, depending on the range of environments in the sample. That’s a definition problem. Further, what should we count as ‘genetic’? Gene expression can depend on the environment of the parents, for example (DNA methylation, etc). That’s an environmental inheritance. I just think there is an old way of talking about these things that needs to go away in light of current knowledge.
I agree with you that we still can learn a lot from these studies.
The definition of ‘heritable’ being underspecified (since you have to specify what population of environments you’re considering) is not the same as being incoherent.
I agree. Good point.