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

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

#11

Post by gjm11 »

donniefitz2 wrote: post #6

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 diff…

Oh, twaddle. What differencse between "identical" twins challenge is the idea that being is purely genetic. Fortunately, no one actually believes in that idea.

All apples of a given variety are (I think) genetically identical, because of the way they're grown. (You start with a rootstock of some kind of apple tree that doesn't produce nice fruit, and then graft on the thing you actually want. This has to be done because if you grow apples from seed you tend to get trees that are very unlike their parents.) But -- gasp! -- not all Granny Smith (or whatever) applies look identical. Is this evidence for a non-physical component to applehood?

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

#12

Post by Tichy »

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.

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

#13

Post by gjm11 »

patio11 wrote: post #10
philwelch wrote: post #8

Earlier quoted context omitted.

(Identical) twins are genetically identical. (edited--thanks patio11)

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…

Much, much smaller than 1/(2^48). You don't get whole chromosomes from each parent.

Suppose one of your father's chromosome pairs is (ABCDEF,abcdef) and your mother's corresponding pair is (PQRSTU,pqrstu). Then you might be, e.g., (ABcdef,pQrSTu). Except that actually there are hugely many points at which crossover (i.e., a switch between ABCDEF and abcdef) can occur, and it can happen a variable (though usually not very large) number of times on each chromosome.

Oh, and after that you'll have maybe 100 mutations (which could be anywhere) relative to your parents.

Crude back of envelope calculation: you have on the order of 10^8 base pairs on each chromosome; there might typically be two crossovers per chromosome pair from each parent, giving you on the order of 10^16 possibilities for the chromosome you get from your father, the same for your mother, and hence ~ 10^32 possibilities for each of your chromosome pairs, so ~ 10^700 possibilities in all. Then you have ~100 extra mutations in your ~10^9 base pairs, giving another 10^900 possibilities; so there are ~ 10^1600 ways to make a typical human child's genome from a given pair of parents.

That's a super-crude calculation, of course, but it's much nearer the right order of magnitude 2^48.

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

#14

Post by tome »

donniefitz2 wrote: post #6

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 diff…

In the back of my mind I recall a study that said identical twins raised separately will often act differently to try to differentiate themselves, whereas identical twins raised separately have no such motivation and thus often end up more similar.

If anyone could verify my hazy recollection I'd be most interested.

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

#16

Post by Sforlips »

donniefitz2 wrote: post #6

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 diff…

1) even if their environment was very similar, it wasn't identical, if only because they interacted with each other. As you probably know, living system are roughly chaotic (except that, formally, chaotic systems are strictly deterministic, whereas determinism in the real world is debatable), and a tiny difference at one time point can have drastic consequences later on.

2) identical genes can lead to different phenotypes. Take the example of handedness. There is a dominant allele for right handedness and a recessive allele for random handedness. The people with two random genes have 0.5 chances of being right handed, and 0.5 chances to be left handed or ambidextrous.

The same gene also determines if the hairwhorl turns clockwise or counter-clockwise, with the same behaviour. The dominant allele mean clockwise, and the recessive one is random. AFAIK, in the random case, handedness and whorl direction are independant.

I don't think that your example is a good case for dualism.

Edit: Were you trolling?

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

#17

Post by berntb »

JCThoughtscream wrote: post #2

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…

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.

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

#18

Post by berntb »

xtho wrote: post #15

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.

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.2...

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

#19

Post by ZeroGravitas »

Tichy wrote: post #12

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…

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.

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

#20

Post by pbhjpbhj »

ZeroGravitas wrote: post #19
Tichy wrote: post #12

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…

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.

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.

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