I followed up on some of the links, and found a discussion as to whether the genetic mutations that predispose Askenasi Jews to certain diseases might also increase intelligence. Arguments in favor suggested that the value placed on intelligence in Jewish culture and their niche in the European economy selected for these mutations. Others claimed that the diseases might be due to the Founder Effect -- when a population derives from just a few ancestors, new inherited diseases tend to result.

To the extent that intelligence is heritable, the Founder Effect can also explain the frequency of high IQs among Ashkenazi Jews. About six months ago I saw an article on MSN about research that traced the maternal line of Askenasi Jewish women. Forty percent of them could be traced to just four women who lived somewhere from 1,000 to 2,000 years ago. I am guessing that this means that just four founding families provide 40% of the Askanasi Jewish gene pool.

My theory is that roughly around the time of Charlemagne four highly intelligent and learned Jews from Italy were recruited to serve as court Jews in the Holy Roman Empire. Several hundred years before the Crusades brought antisemitic persecution, these Jews would have been highly paid and would have had many children. These four families would have provided spouses for each others' children for three or four generations, producing, say, a thousand offspring. This thousand might have provided 40% of the Askenazi gene pool, the other 60% coming from later Jewish arrivals and gentiles (converts, wartime rape, and occasional hanky-panky).

If intelligence has a genetic component, then the 40% of the Askenasi Jewish gene pool provided by brilliant court Jews could have noticeably and permanently boosted the average Askanasi Jewish intelligence.

My guess is that the Founder Effect contributed to both the genetic diseases to which Ashkenasi Jews are prone and the unusual rate of high IQs -- regardless whether the same genetic mutations responsible for the former are also responsible for the latter. If the Jewish culture and medieval economic niche selected for intelligence, then this would only amplify the Founder Effect on intelligence.

Permit me my skepticism.

First, genetic ancestry tests focus on either the y-chromosome or on mitochondrial DNA. The former represents a line of descent through the male line, the latter the female line. The problem is that you *don't* have two ancestors 1000 years ago. You have hundreds. And most of those ancestors are not traceable using y-chromosome or mitochondrial DNA.

Thus what is scientifically known about the ancestry of Askenazi Jews is very little. We simply do not have the tools to evaluate it very well.

Second, IQ testing is known to be influenced by much more than heredity. Environmental factors matter - such as cultural emphasis of education and valuation of literacy, family size, parental involvement in child education, nutrition, exposure to toxins and diseases. How much of intelligence is heritable is a very large unknown.

My skepticism is screaming alarms. I see people climbing out onto very narrow limbs to draw unwarranted conclusions about heredity - such as William's amusingly-told but unsupported hypothesis that superior intelligence and susceptibility to disease is linked in Jewish populations.

Still, science must show no fear. Hypotheses are allowed, and so is research to confirm or refute them. Perhaps Jews are the beneficiaries of a heritable advantage; learning that's so and discovering the genes responsible could lead to interesting developments for all of humanity. But I'm by no means sanguine that science will deliver us to this particular doorstep.

"How much of intelligence is heritable is a very large unknown"

I am confused. We know darned well that intelligence is primarily genetic from studies of identical twins. Even reared apart, their intelligences strongly correlate (R-squared > .75). Many other personality traits correlate strongly as well. On the other hand, sharing the same parents, womb, or schools have effects that are barely measurable.

Or perhaps you believe in some mystical magical force that connects twins through the aether, so that they think alike without ever having met?

Urgelt,

IQ testing is known to be influenced by much more than heredity.

In adults, heritability accounts for about 82% of the total variance. The remainder is accounted for by the non-shared environment.

Environmental factors matter - such as cultural emphasis of education

Education has nothing to do with intelligence. It does not change g in any way, nor does family or society.

and valuation of literacy, family size,

You got one right. Parity was previously believed to affect intelligence, then a paper came along that argued rather strongly that the parity effect was an artifact. Then (this year) a new paper was published that showed, from a large data set, that first born children are indeed statistically more intelligent than their siblings.

parental involvement in child education,

Parents influence IQ only by providing genes. The family environment has no effect on IQ at all.

nutrition, exposure to toxins and diseases.

Yes. These are real, although small in all industrialized countries.

"How much of intelligence is heritable is a very large unknown"

In childhood: about 45%
In late adolescence & early adulthood: about 70%
In later adulthood: about 82%

I am confused. We know darned well that intelligence is primarily genetic from studies of identical twins.

Yes, good for you! Few people here understand that basic fact. You are NOT confused.

Even reared apart, their intelligences strongly correlate (R-squared > .75).

Right!

Many other personality traits correlate strongly as well. On the other hand, sharing the same parents, womb, or schools have effects that are barely measurable.

Absolutely correct!

The count of people I have found here who are not ignorant has risen to at least 2.

You make a lot of broad statements here about heritability, yet I don't think they are qualified properly and the way I interpret your statements makes me think that you put too much emphasis on genes. The percentages you give differ from the ones I've read although I'd admit I'm probably not as widely read on this subject as you (my favorite author on these topics being Stephen Pinker) but I’d imagine most scientist would laugh at the percentages you give (‘In later adulthood: about 82%’ – the 2 in 82 made me laugh, I would think it would be more like 82.457J. Why is it that children are less hereditarily determined than adults? The more experience the less you learn from experience (?), very counter-intuitive although I’m sure you can respond to this).

You say parents influence IQ only through the genes they pass on, but without language we can agree that children are definitely not intelligent, and without language in the immediate environment, children will not pick up language at all from their genes alone.

You said intelligence is not affected by education, family or society - which I would disagree with, even though I would say that it may be a small affect – but then you go on to say that the first born children are indeed statistically more intelligent than their siblings – a function of family (maybe you need to qualify what you mean by family). I think it’s pretty obvious that savant children are not thought to be very intelligent, and by this comment I would have to conclude that if I had a baby and keep it from any social/physical/intellectual inputs, if that child didn’t die it would be able to score 100 on an IQ test. I think you discount the ‘general’ environment we all share as contributing to intelligence and are just considering the little bit that our environments can differ as ‘environmental influence’.

I think part of the problem lies in the complication involved in measuring differences in environment and which differences are significant and which are not. Don’t get me wrong, I would probably assign just as much importance to genes as to environment in determining intelligence, maybe even more, because I think that in our societies all the proper environmental factors are already there for the large majority of people and therefore the only other place to look is the genes – but by not taking that into consideration it is easy to overemphasize the importance of genes over environment, which has been the recent trend. But as most cautious scientists would claim (Pinker) it is more like 50/50.

General intelligence, btw, is considered by psychology - a controversial science in itself - to be a controversial construct.

Why is it that children are less hereditarily determined than adults? The more experience the less you learn from experience (?), very counter-intuitive although I’m sure you can respond to this).

In children, there is an IQ component that is due to the shared environment. It vanishes in the teen years. With that component gone, heritability rises to about 70%. The additional rise happens, but it may be debatable as to the exact cause. One notion is that some genes are expressed only later in life, as we see in age related traits that are identical in identical twins.


You say parents influence IQ only through the genes they pass on, but without language we can agree that children are definitely not intelligent, and without language in the immediate environment, children will not pick up language at all from their genes alone.

Are you attempting to introduce a specious argument? Why? Surely you know that humans rapidly learn the language or languages around them in childhood. Intelligence is not dependent on grammar or spelling.


You said intelligence is not affected by education, family or society - which I would disagree with, even though I would say that it may be a small affect –

Let's begin by recalling that intelligence is best quantified by g. Now please explain how g is altered by any of the items you listed. So far, no researcher has reported any means of boosting intelligence by any social scheme. If you know how, you should write it up and publish it. The world will be grateful.


but then you go on to say that the first born children are indeed statistically more intelligent than their siblings – a function of family (maybe you need to qualify what you mean by family).

The first born phenomenon relates to parity. That is all you need to know. If you are not familiar with parity, you can find information about it on the web.


I think it’s pretty obvious that savant children are not thought to be very intelligent,

Right. They are accounted for in the studies of populations. They, fortunately, are not numerous.


and by this comment I would have to conclude that if I had a baby and keep it from any social/physical/intellectual inputs, if that child didn’t die it would be able to score 100 on an IQ test.

What? Do you understand that everything that is said about intelligence is statistically based? A bright couple can have a retarded child and a dull couple can have a brilliant child. The odds of it happening are low, but not zero. Without regression analysis and similar tools, it would be impossible to study phenomena where there are multiple variables acting simultaneously.

Don’t get me wrong, I would probably assign just as much importance to genes as to environment in determining intelligence,

How would you determine the numbers? By guessing, or by experiment? The numbers I have presented were not opinions, they were the results of large studies. I have previously explained how heritability is calculated (4 ways). Would you tell us your methodology?

Thanks for responding MorganLee, I am quite interested in this topic although it seems I’m not as well informed as you appear to be. I do have a few comments and questions for you regarding your response.

I’m not sure how to interpreter what you wrote about children being less hereditarily determined than adults, so I guess I’ll have to read up more about that. It appears obvious to me that there is an IQ component that is due to shared environment (as well as unshared environment and genetics). When the shared environment component decreases (I don’t see how it can disappear, because we all have the shared environment of the country we live in, the media, government, etc. these things don’t disappear) the unshared environment component would logical replace some of the shared component (we do grow up to have different experience, ideas and peers, etc. more increasingly over time).

Are you attempting to introduce a specious argument? Why? Surely you know that humans rapidly learn the language or languages around them in childhood. Intelligence is not dependent on grammar or spelling.

Well, I’m not knowingly introducing a specious argument, and this comment does not attempt explain why it is specious. I DO know that infants acquire language rapidly – not humans, only very young humans - as they NEED to have a language in their ENVIROMENT in order to learn it. I’m sure that the genes determine how well a child CAN learn – but they learn from something (environment) and indeed I am arguing for the environment as a greater factor in intelligence. I didn’t say intelligence is dependent on grammar or spelling, my comment reads LANGUAGE. There are indeed certain concepts, ideas, abilities that can’t be learned without language. Indeed some (not I) philosophers/psychologists would say you can’t even be a fully conscious being without language.

Let's begin by recalling that intelligence is best quantified by g. Now please explain how g is altered by any of the items you listed. So far, no researcher has reported any means of boosting intelligence by any social scheme. If you know how, you should write it up and publish it. The world will be grateful.

I’ve read that there is a strong correlation between intelligence and g, but they are not the same thing, but for your sake I will assume this. The only item I’m listing is environment and I will give an example that I’m sure you will have to concede and which has ALREADY been published. For one example I’ve read that it has been shown that you CAN study for IQ tests and do much better than without studying (read ENVIROMENT – the other example is first borns which I will extrapolate on next). So the third statement above would appear to be completely false, unless I’m reading it wrong, in which case please help me out.

The first born phenomenon relates to parity. That is all you need to know. If you are not familiar with parity, you can find information about it on the web.

OK, I've read up a little on this phenomenon and I don’t see how it relates to the first born phenomenon. I’ve read that the first born phenomenon is non-biological because…

“The article explains that the better scores for the firstborn are not biological because when an older sibling dies in infancy (age < 1 year), then the younger sibling's IQ is more like that of a firstborn sibling. “ You can find the article at <link>

The reasons why the first born has a higher IQ can be related to the parents excitement of having a new child and therefore spending more time with them and the first born having more responsibility and having to teach younger siblings (again ENVIROMENT).

Right. They are accounted for in the studies of populations. They, fortunately, are not numerous.

Sweet, score one for me. J

What? Do you understand that everything that is said about intelligence is statistically based? A bright couple can have a retarded child and a dull couple can have a brilliant child. The odds of it happening are low, but not zero. Without regression analysis and similar tools, it would be impossible to study phenomena where there are multiple variables acting simultaneously.

What? Yes I understand statistics and that you’ve read many papers on this. I still have the opinion that you don’t understand my point. You said, and I quote “The family environment has no effect on IQ at all.” So you meant “Statistically, the family environment has no effect on IQ at all.” So if we study many savant children and compared them with many children brought up in developed countries there would be no STATISTICAL difference? Huh?

How would you determine the numbers? By guessing, or by experiment? The numbers I have presented were not opinions, they were the results of large studies. I have previously explained how heritability is calculated (4 ways). Would you tell us your methodology?

I don’t determine the numbers – and I would accept any numbers based on the little we know about intelligence/ hereditability / environmental influence. Oh, you read some large studies? Forget everything I said then. For a topic this complex I would be a little more critical of these studies then you seem to be. Although. if you could point me to one of these studies I would very much appreciate it.

Thanks

When the shared environment component decreases (I don’t see how it can disappear, because we all have the shared environment of the country we live in, the media, government, etc. these things don’t disappear) the unshared environment component would logical replace some of the shared component (we do grow up to have different experience, ideas and peers, etc. more increasingly over time).

You can easily find a copy of this on the web:

Rushton, J.P. and Jensen, A.R. (2005). Thirty Years of Research on Race Differences in Cognitive Ability. Psychology, Public Policy, and Law, Vol. 11, No. 2, 235-294.

Turn to Figure 3 (page 252 of the journal) and you will see what happens.

I’ve read that there is a strong correlation between intelligence and g, but they are not the same thing, but for your sake I will assume this. The only item I’m listing is environment and I will give an example that I’m sure you will have to concede and which has ALREADY been published. For one example I’ve read that it has been shown that you CAN study for IQ tests and do much better than without studying (read ENVIROMENT – the other example is first borns which I will extrapolate on next). So the third statement above would appear to be completely false, unless I’m reading it wrong, in which case please help me out.

Tests load on only three factors: g, s, and e. The sum of the squares of these must equal 1.
s = specificity
e = random error

Study increases the s loading. That decreases the g loading. So, what happens is that the test score is artificially boosted and it is less accurate. There is a limit to both the amount of boost and its duration. The boost is an error, not intelligence. It is very difficult to get copies of the high quality IQ tests that are used by professionals. But, the SAT has spawned an entire industry based on teaching to the test.

“The article explains that the better scores for the firstborn are not biological because when an older sibling dies in infancy (age < 1 year), then the younger sibling's IQ is more like that of a firstborn sibling. “ You can find the article at <link>

This one has gone one way and the other. I don't contend that it has been resolved. The paper I mentioned is this:
T. Bjerkedal, P. Kristensen, G. A. Skjeret, J. I. Brevik, Intelligence 35, 10.1016/j.intell.2007.01.004 (2007).

You said, and I quote “The family environment has no effect on IQ at all.” So you meant “Statistically, the family environment has no effect on IQ at all.” So if we study many savant children and compared them with many children brought up in developed countries there would be no STATISTICAL difference? Huh?

I suppose I need to insert the word "correlation" into every sentence. When a meaningfully large, stochastic sample is studied, there is no correlation between IQ and the shared environment among adults. If someone studies many savant children, that study is not a stochastic sampling of the population.

For a topic this complex I would be a little more critical of these studies then you seem to be. Although. if you could point me to one of these studies I would very much appreciate it.

If "these studies" means savants, I can't point you to appropriately large studies. If you mean something else, I didn't get it.