I don’t think one of the claims, that “Twin studies are flawed in methodology. Twins, even identical twins, simply do not have exactly the same DNA”, is true. As I see, it is not supported by the link and the study.
The difference of 5.2 out of 6 billion letters that identical twins have on average is not something that makes their DNA distinct enough to make the correlations between being identical tweens or not and having something in common more often to be automatically invalid.
One of the people involved in the study is cited: “Such genomic differences between identical twins are still very rare. I doubt these differences will have appreciable contribution to phenotypic [or observable] differences in twin studies.”
Twin studies being something we should be able to rely on seems like a part of the current scientific view, and some EA decisions might take such studies into consideration.
I think it’s important not to compromise our intellectual integrity even when we debunk foundations for awful and obviously wrong beliefs that are responsible for so much unfairness and suffering that exist in our world and for so many deaths.
I think if the community uses words that are persuasive but don’t contain actually good evidence, then even if we’re arguing for the truth that’s important and impactful to spread, in the long-term, this might lead to people putting less trust in any of our words arguing for the truth and more people believing something harmful and untrue. And on the internet, there are a lot of words containing bad arguments for the truth because it’s easy for people to be in the mode of finding persuasive arguments, which don’t necessarily have to be actually good evidence.
I think it’s really important for the EA community to be epistemically honest and talk about the actual reasons we have for believing something, instead of trying to find the most persuasive list of reasons for believing in what we believe in and just copying it without verifying that all the reasons are good and should update people in the claimed direction.
These are two separate links for two separate claims. ‘Twin studies are flawed in methodology.’ and ‘Twins, even identical twins, simply do not have exactly the same DNA.’, both of which are true. The confidence in the proposed HBD conclusions is simply not warranted by the evidence.
Oops! Sorry, I only discovered the second link; but before writing my comment, I looked up the first myself.
I’m not a biologist and will probably defer to any biologist entering this thread and commenting on the twin studies.
Twins (mostly, as the linked study shows) do not have exactly the same DNA. But it doesn’t seem to be relevant. The relevant assumption is that there’s almost no difference between the DNAs of “identical” twins and a large difference between the DNAs of non-identical reared-together twins, which is true despite a couple of random mutations per 6 billion letters.
The next two linked articles are paywalled. Is there somewhere to read them?
The third is a review of a short book, available after a sign-up, and it says that “some studies on twins are good, some bad”, and the author feels, but “doesn’t actually know” that the reviewed one is good. The reviewed book performed a study on twins and noticed there isn’t much of a difference between the correlation of the similarity of many personality traits with whether people are identical twins, and concluded that, since you’d expect to see a difference if the traits have different degree of heritability, many personality traits are results of the environment.
How is this an evidence that twin studies are flawed and shouldn’t be used? If that’s a correct study, it’s just evidence that personality traits are mostly formed by environment (which is something I already believe and have believed for the most of my life), but, e.g., why would this be relevant for a discussion of whether or not some disease has a genetic component to it, when a twin study shows that there is?
It’s important to carefully compare the numbers; but obviously there are things that identical twins have in common more often then non-identical twins, because these things are heritable at to larger or lesser degree; like hair color or height.
Of course, any study makes some underrepresentation of humanity. But if your study is about the degree of heredity of something and not about twins, why would this matter? If there’s a difference between adopted identical and non-identical twins that’s better explained by genetics (e.g., non-identical twins would have a different height more often), why does it matter how well they represent twins in general? Unless you’re studying how likely people are to be adopted, I don’t understand the claim.
The last link is paywalled, but again, why would this affect the difference between identical twins and non-identical twins? Until a year ago, I kept secret that I’m bi and would’ve kept it secret from scientists; but I don’t think this kind of thing affects conclusions you’d make if identical twins answered identically to some question more often than non-identical twins (e.g., imagine a society where people with green eyes are persecuted and a lot of them use contact lenses. Some would still say the truth, in confidence, to scientists; and the number of identical twins telling the same answer would be greater than the amount of non-identical twins telling the same answer, and the scientists will correctly infer this to be evidence for the heritability of eye color, even though a lot of twins would lie about their eye color).
So while it’s possible to just compare full DNAs and account for lots of different factors (all sorts of various environmental conditions that might be different between the subjects of the study) to find out whether DNA correlates with eye color, it’s much easier to do a twin study, and a strong correlation there will be a strong evidence
It’s fine. Studies don’t just use identical twins but twins in general. You are equating my two claims and attacking claims that I haven’t even made, I never talked about “whether or not some disease has a genetic component to it, when a twin study shows that there is?”. I made a claim that twins, even identical twins, don’t share exactly the same DNA and provided a link to an article that gave more information, and I made a second claim that twin studies were flawed and provided that claim with a link to an article with more information about that. All this stuff about that it can’t help us find diseases or that twin studies “shouldn’t be used” are claims I never made.
EDIT:
I’m not a biologist and will probably defer to any biologist entering this thread
For the record my study has some biostatistics, but it isn’t my strongest field and I’m mostly leaning on stuff my professors have explained:
I will also probably defer to a biologist/biostatistician.
I don’t think one of the claims, that “Twin studies are flawed in methodology. Twins, even identical twins, simply do not have exactly the same DNA”, is true. As I see, it is not supported by the link and the study.
The difference of 5.2 out of 6 billion letters that identical twins have on average is not something that makes their DNA distinct enough to make the correlations between being identical tweens or not and having something in common more often to be automatically invalid.
One of the people involved in the study is cited: “Such genomic differences between identical twins are still very rare. I doubt these differences will have appreciable contribution to phenotypic [or observable] differences in twin studies.”
Twin studies being something we should be able to rely on seems like a part of the current scientific view, and some EA decisions might take such studies into consideration.
I think it’s important not to compromise our intellectual integrity even when we debunk foundations for awful and obviously wrong beliefs that are responsible for so much unfairness and suffering that exist in our world and for so many deaths.
I think if the community uses words that are persuasive but don’t contain actually good evidence, then even if we’re arguing for the truth that’s important and impactful to spread, in the long-term, this might lead to people putting less trust in any of our words arguing for the truth and more people believing something harmful and untrue. And on the internet, there are a lot of words containing bad arguments for the truth because it’s easy for people to be in the mode of finding persuasive arguments, which don’t necessarily have to be actually good evidence.
I think it’s really important for the EA community to be epistemically honest and talk about the actual reasons we have for believing something, instead of trying to find the most persuasive list of reasons for believing in what we believe in and just copying it without verifying that all the reasons are good and should update people in the claimed direction.
These are two separate links for two separate claims. ‘Twin studies are flawed in methodology.’ and ‘Twins, even identical twins, simply do not have exactly the same DNA.’, both of which are true. The confidence in the proposed HBD conclusions is simply not warranted by the evidence.
Many twin studies have the assumption that they share 100% of their DNA (which is false) andthat they share the exact same environment (which is also false). This leads to underestimating environmental factors and underestimating non-genetic biological factors.
Furthermore, separated twin pairs, identical or fraternal, are generally separated by adoption. This makes them unrepresentative of twins as a whole and there can be some issues of undetected behaviors in the case of behaviors that many people keep secret presently or in their earlier lives.
Oops! Sorry, I only discovered the second link; but before writing my comment, I looked up the first myself.
I’m not a biologist and will probably defer to any biologist entering this thread and commenting on the twin studies.
Twins (mostly, as the linked study shows) do not have exactly the same DNA. But it doesn’t seem to be relevant. The relevant assumption is that there’s almost no difference between the DNAs of “identical” twins and a large difference between the DNAs of non-identical reared-together twins, which is true despite a couple of random mutations per 6 billion letters.
The next two linked articles are paywalled. Is there somewhere to read them?
The third is a review of a short book, available after a sign-up, and it says that “some studies on twins are good, some bad”, and the author feels, but “doesn’t actually know” that the reviewed one is good. The reviewed book performed a study on twins and noticed there isn’t much of a difference between the correlation of the similarity of many personality traits with whether people are identical twins, and concluded that, since you’d expect to see a difference if the traits have different degree of heritability, many personality traits are results of the environment.
How is this an evidence that twin studies are flawed and shouldn’t be used? If that’s a correct study, it’s just evidence that personality traits are mostly formed by environment (which is something I already believe and have believed for the most of my life), but, e.g., why would this be relevant for a discussion of whether or not some disease has a genetic component to it, when a twin study shows that there is?
It’s important to carefully compare the numbers; but obviously there are things that identical twins have in common more often then non-identical twins, because these things are heritable at to larger or lesser degree; like hair color or height.
Of course, any study makes some underrepresentation of humanity. But if your study is about the degree of heredity of something and not about twins, why would this matter? If there’s a difference between adopted identical and non-identical twins that’s better explained by genetics (e.g., non-identical twins would have a different height more often), why does it matter how well they represent twins in general? Unless you’re studying how likely people are to be adopted, I don’t understand the claim.
The last link is paywalled, but again, why would this affect the difference between identical twins and non-identical twins? Until a year ago, I kept secret that I’m bi and would’ve kept it secret from scientists; but I don’t think this kind of thing affects conclusions you’d make if identical twins answered identically to some question more often than non-identical twins (e.g., imagine a society where people with green eyes are persecuted and a lot of them use contact lenses. Some would still say the truth, in confidence, to scientists; and the number of identical twins telling the same answer would be greater than the amount of non-identical twins telling the same answer, and the scientists will correctly infer this to be evidence for the heritability of eye color, even though a lot of twins would lie about their eye color).
So while it’s possible to just compare full DNAs and account for lots of different factors (all sorts of various environmental conditions that might be different between the subjects of the study) to find out whether DNA correlates with eye color, it’s much easier to do a twin study, and a strong correlation there will be a strong evidence
It’s fine.
Studies don’t just use identical twins but twins in general. You are equating my two claims and attacking claims that I haven’t even made, I never talked about “whether or not some disease has a genetic component to it, when a twin study shows that there is?”. I made a claim that twins, even identical twins, don’t share exactly the same DNA and provided a link to an article that gave more information, and I made a second claim that twin studies were flawed and provided that claim with a link to an article with more information about that. All this stuff about that it can’t help us find diseases or that twin studies “shouldn’t be used” are claims I never made.
EDIT:
For the record my study has some biostatistics, but it isn’t my strongest field and I’m mostly leaning on stuff my professors have explained:
I will also probably defer to a biologist/biostatistician.