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Miscalibrated Minds: Why Don’t We Apply What We Know About Twins to Everybody?

12 points by MikeCapone 17y ago

JCThoughtscream 17y ago
I'd contest the statement that "nobody’s surprised when identical twins turn out to have very similar bodies (weight, muscle mass, etc), even into adulthood." From the research I remember reading about, there does seem to be some genuine level of surprise as to how much influence genetics has over even twins separated at or near birth - and that the level of genetic determinism that twins exhibit is certainly rather controversial even amongst those that study them.
- berntb 17y ago
  Twins also shares a common pre-birth environment, with the same environmental influences. I've read the argument that probably helps a lot to make them similar.
  - xiaoma 17y ago
    Actually, those identical who grow up apart (in the same country) are more similar to each other than those who grow up together. Also, there's quite a bit of research comparing monozygotic (i.e. "identical") and dizygotic twins. The differences in correlation are stark. Twins who share the same genes are far, far more alike than those who don't: http://en.wikipedia.org/wiki/File:Heritability-from-twin-correlations1.jpg http://en.wikipedia.org/wiki/File:Heritability-from-twin-cor...
    - berntb 17y ago
      >>Actually, those identical who grow up apart (in the same country) are more similar to each other than those who grow up together. Not relevant. I noted that the environment in the womb was very similar for twins, which certainly influences a lot. (It was a nitpicking note, I am aware of the strength of the twin arguments in general and not one of those idealists which dislikes arguments which goes against Marx -- or whatever it now is that the twin arguments contradict...)
a-priori 17y ago
Or, maybe, twins share similar thought patterns and therefore make similar lifestyle choices (how much to eat, how often to exercise, and so on) and that's why they share similar weights and muscle mass. That said, the nature/nurture pendulum has been stuck on the "nurture" side for a while, and it's now starting swinging back to the middle where it belongs. It's got a ways to go though. I'm reading Steven Pinker's The Blank Slate now, and I highly recommend it to people who are interested in this topic.
- pstuart 17y ago
  It's all nature. Nurture is what you do with it.
c0nsilience 17y ago
Like a-priori, I have read The Blank Slate. I'm pretty familiar with Pinker's work and the article linked here doesn't say much. As a matter of fact, it doesn't say anything helpful at all. "Why don't we apply what we know about twins to everybody?" Well, it's because the role that genetics plays in behavior isn't clear cut and well-defined. Full disclosure: I side with nature over nurture when it comes to behavior, but I believe it's probably 60/40 or 70/30, meaning environment still plays a major role. Sure, the cases of identical twins separated at birth is compelling. They sometimes make the same career decisions and even marry and divorce and remarry people with the same exact names. But what about identical twins who turn out to be of different sexual orientation? What about identical twins who are almost nothing alike but raised in the same home? Genetics definitely needs to be recognized as a significant influence on behavior and human nature, but there's a reason we don't apply identical twins studies and findings to everyone. I can't believe anyone would say, "If it applies to these people, why don't we apply it to everyone else?" It rarely ever works that way.
donniefitz2 17y ago
Twins may be identical physically, but they present a challenge to the assumption that being is merely physical because they are often completely different when it comes to who they are (and what is that, really?) I have lived with twins for 3 years (married to one of them) and you couldn't find two people more different. Physically they look the same, but as far as personality, you couldn't find two people more different. They were both "nurtured" from the same woman, same environment, yet they are opposites. I think there is an ontological question raised. Is there a non-physical component to our existence? Something to think about.
- latortuga 17y ago
  Why does a non-physical component need to be invoked? Why could there not simply be genetic mutation that affects personality but not physical stature? It seems to me that there's no reason to believe some non-physical component is at work until the physical components have been ruled out.
  - philwelch 17y ago
    (Identical) twins are genetically identical. (edited--thanks patio11)
    - patio11 17y ago
      Monozygotic (identical) twins are. Dizygotic (fraternal) twins are not. Actually, clarification to the clarification: fraternal twins, like any two siblings from the same parents, are merely highly unlikely to be (close to) genetically identical. For any given chromosome, you either get one of Mom's or one of Dad's. That gives you a finite number of possible chromosomal choices. Since they're essentially chosen with replacement between fertilizations (in the discrete sense of "chosen with replacement", its not like the egg says "OK, I'm done with this X chromosome mom, you can have it back now"), you could randomly end up with two siblings (and, by extension, two fraternal twins) with the same chromosome choices (i.e. pretty close to genetically identical, allowing for some minor and likely consequence-less mutation). My naive calculation of the probability of any two siblings being genetically identical without being identical twins is 1 / (2 ^ 48), though. :)
latortuga 17y ago
As I'm about half done with Good Calories, Bad Calories, this post rather resonates. My mother is an identical twin and she is about as equal in stature to her sister as you can be. It's curious to me that I've always accepted that since they're twins, they must have similar body types. It is very quickly apparent to me that, because they live apart and don't eat the same things, weight and/or body type must have some genetic or metabolic component unrelated to consumption or exercise. The disconnect between my observation and my previous thinking of obesity being related to will power or exercise habits is sort of mind blowing.
- pbhjpbhj 17y ago
  Are you sure they don't eat the same things? They grew up together? This is most likely to mean that they eat a similar diet - if they co-habit with people outside the others social setting then that's probably going to lead away from similar diets. My cooking is very much influenced by the things my mother cooked for me; I also borrow recipes from my sister occasionally.
Tichy 17y ago
Only yesterday there was another submission about a twin who weighs 15 pounds (or kg?) more than his brother. Really, what DO we know about twins? Most twins also grow up in the same environment and with the same education. In fact when I looked up some IQ studies of twins, it turns out that there really aren't many cases of twins that have not grown up together. Usually some war happenings were the background. As a result, those studies don't typically look like what you would a scientific experiment to look like. Some separated twins might only be discovered in their 50ies, others in their teens. You can not just go ahead and say "let's look at 50 pairs of twins, of which one grew up in a poor family and one in a rich family", because you will not find 50 such twins from the same era. Maybe you find some poor twin who grew up in the 50ies, and another poor twin who grew up in the 80ies, or one grew up in Africa and the other in Europe, so comparison already becomes questionable.
- ZeroGravitas 17y ago
  From the other story: "For a start I was 15kg heavier than my brother." but... "Of the thousands of twins enrolled in the research program only 10 were more different in weight than us." So it seems that in general twins weigh roughly the same.
  - pbhjpbhj 17y ago
    15kg is quite a lot. Most men in my street (by sight) would be within 15kg of me, I'm about 83kg ~ 13 stone (slightly over WolframAlpha's reported median USA male weight in 2006). I think the chance of being more than 15kg outside the weight of someone who has grown up in the same lifestyle and with the same food opportunity is probably pretty low.
    - xiaoma 17y ago
      When I went back to the states, I saw people that weighed 50kg more than others near them pretty much every time I went out.
  - Tichy 17y ago
    "So it seems that in general twins weigh roughly the same." It should be easy to study the eating habits of these twins. In most cases, why should they differ much, if they have been raised in the same household?
xtho 17y ago
Looking at twins that grew up in the same environment isn't all that appropriate for making statements about the dominance of genes. Of course, if the data doesn't fit our assumptions we could always cite Cyril Burt or do it like he did.
- berntb 17y ago
  The jury seems to still be out on Burt. Hamilton as a defender is not bad... http://en.wikipedia.org/wiki/Cyril_Burt#.22The_Burt_Affair.22 http://en.wikipedia.org/wiki/Cyril_Burt#.22The_Burt_Affair.2...

12 points by MikeCapone 17y ago

I'd contest the statement that "nobody’s surprised when identical twins turn out to have very similar bodies (weight, muscle mass, etc), even into adulthood." From the research I remember reading about, there does seem to be some genuine level of surprise as to how much influence genetics has over even twins separated at or near birth - and that the level of genetic determinism that twins exhibit is certainly rather controversial even amongst those that study them.

berntb 17y ago
Twins also shares a common pre-birth environment, with the same environmental influences. I've read the argument that probably helps a lot to make them similar.
- xiaoma 17y ago
  Actually, those identical who grow up apart (in the same country) are more similar to each other than those who grow up together. Also, there's quite a bit of research comparing monozygotic (i.e. "identical") and dizygotic twins. The differences in correlation are stark. Twins who share the same genes are far, far more alike than those who don't: http://en.wikipedia.org/wiki/File:Heritability-from-twin-correlations1.jpg http://en.wikipedia.org/wiki/File:Heritability-from-twin-cor...
  - berntb 17y ago
    >>Actually, those identical who grow up apart (in the same country) are more similar to each other than those who grow up together. Not relevant. I noted that the environment in the womb was very similar for twins, which certainly influences a lot. (It was a nitpicking note, I am aware of the strength of the twin arguments in general and not one of those idealists which dislikes arguments which goes against Marx -- or whatever it now is that the twin arguments contradict...)

a-priori 17y ago

Or, maybe, twins share similar thought patterns and therefore make similar lifestyle choices (how much to eat, how often to exercise, and so on) and that's why they share similar weights and muscle mass. That said, the nature/nurture pendulum has been stuck on the "nurture" side for a while, and it's now starting swinging back to the middle where it belongs. It's got a ways to go though. I'm reading Steven Pinker's The Blank Slate now, and I highly recommend it to people who are interested in this topic.

pstuart 17y ago
It's all nature. Nurture is what you do with it.

c0nsilience 17y ago

Like a-priori, I have read The Blank Slate. I'm pretty familiar with Pinker's work and the article linked here doesn't say much. As a matter of fact, it doesn't say anything helpful at all. "Why don't we apply what we know about twins to everybody?" Well, it's because the role that genetics plays in behavior isn't clear cut and well-defined. Full disclosure: I side with nature over nurture when it comes to behavior, but I believe it's probably 60/40 or 70/30, meaning environment still plays a major role. Sure, the cases of identical twins separated at birth is compelling. They sometimes make the same career decisions and even marry and divorce and remarry people with the same exact names. But what about identical twins who turn out to be of different sexual orientation? What about identical twins who are almost nothing alike but raised in the same home? Genetics definitely needs to be recognized as a significant influence on behavior and human nature, but there's a reason we don't apply identical twins studies and findings to everyone. I can't believe anyone would say, "If it applies to these people, why don't we apply it to everyone else?" It rarely ever works that way.

donniefitz2 17y ago

Twins may be identical physically, but they present a challenge to the assumption that being is merely physical because they are often completely different when it comes to who they are (and what is that, really?) I have lived with twins for 3 years (married to one of them) and you couldn't find two people more different. Physically they look the same, but as far as personality, you couldn't find two people more different. They were both "nurtured" from the same woman, same environment, yet they are opposites. I think there is an ontological question raised. Is there a non-physical component to our existence? Something to think about.

latortuga 17y ago
Why does a non-physical component need to be invoked? Why could there not simply be genetic mutation that affects personality but not physical stature? It seems to me that there's no reason to believe some non-physical component is at work until the physical components have been ruled out.
- philwelch 17y ago
  (Identical) twins are genetically identical. (edited--thanks patio11)
  - patio11 17y ago
    Monozygotic (identical) twins are. Dizygotic (fraternal) twins are not. Actually, clarification to the clarification: fraternal twins, like any two siblings from the same parents, are merely highly unlikely to be (close to) genetically identical. For any given chromosome, you either get one of Mom's or one of Dad's. That gives you a finite number of possible chromosomal choices. Since they're essentially chosen with replacement between fertilizations (in the discrete sense of "chosen with replacement", its not like the egg says "OK, I'm done with this X chromosome mom, you can have it back now"), you could randomly end up with two siblings (and, by extension, two fraternal twins) with the same chromosome choices (i.e. pretty close to genetically identical, allowing for some minor and likely consequence-less mutation). My naive calculation of the probability of any two siblings being genetically identical without being identical twins is 1 / (2 ^ 48), though. :)

latortuga 17y ago

As I'm about half done with Good Calories, Bad Calories, this post rather resonates. My mother is an identical twin and she is about as equal in stature to her sister as you can be. It's curious to me that I've always accepted that since they're twins, they must have similar body types. It is very quickly apparent to me that, because they live apart and don't eat the same things, weight and/or body type must have some genetic or metabolic component unrelated to consumption or exercise. The disconnect between my observation and my previous thinking of obesity being related to will power or exercise habits is sort of mind blowing.

pbhjpbhj 17y ago
Are you sure they don't eat the same things? They grew up together? This is most likely to mean that they eat a similar diet - if they co-habit with people outside the others social setting then that's probably going to lead away from similar diets. My cooking is very much influenced by the things my mother cooked for me; I also borrow recipes from my sister occasionally.

Tichy 17y ago

Only yesterday there was another submission about a twin who weighs 15 pounds (or kg?) more than his brother. Really, what DO we know about twins? Most twins also grow up in the same environment and with the same education. In fact when I looked up some IQ studies of twins, it turns out that there really aren't many cases of twins that have not grown up together. Usually some war happenings were the background. As a result, those studies don't typically look like what you would a scientific experiment to look like. Some separated twins might only be discovered in their 50ies, others in their teens. You can not just go ahead and say "let's look at 50 pairs of twins, of which one grew up in a poor family and one in a rich family", because you will not find 50 such twins from the same era. Maybe you find some poor twin who grew up in the 50ies, and another poor twin who grew up in the 80ies, or one grew up in Africa and the other in Europe, so comparison already becomes questionable.

ZeroGravitas 17y ago
From the other story: "For a start I was 15kg heavier than my brother." but... "Of the thousands of twins enrolled in the research program only 10 were more different in weight than us." So it seems that in general twins weigh roughly the same.
- pbhjpbhj 17y ago
  15kg is quite a lot. Most men in my street (by sight) would be within 15kg of me, I'm about 83kg ~ 13 stone (slightly over WolframAlpha's reported median USA male weight in 2006). I think the chance of being more than 15kg outside the weight of someone who has grown up in the same lifestyle and with the same food opportunity is probably pretty low.
  - xiaoma 17y ago
    When I went back to the states, I saw people that weighed 50kg more than others near them pretty much every time I went out.
- Tichy 17y ago
  "So it seems that in general twins weigh roughly the same." It should be easy to study the eating habits of these twins. In most cases, why should they differ much, if they have been raised in the same household?

xtho 17y ago

Looking at twins that grew up in the same environment isn't all that appropriate for making statements about the dominance of genes. Of course, if the data doesn't fit our assumptions we could always cite Cyril Burt or do it like he did.

berntb 17y ago
The jury seems to still be out on Burt. Hamilton as a defender is not bad... http://en.wikipedia.org/wiki/Cyril_Burt#.22The_Burt_Affair.22 http://en.wikipedia.org/wiki/Cyril_Burt#.22The_Burt_Affair.2...