Intelligence is inherited?

[SkepticLance]

An interesting item in the email version of New Scientist.

 

http://www.newscientist.com/article/mg20126993.300-genes-control-quality-of-brain-connections.html?DCMP=NLC-nletter&nsref=mg20126993.300

 

I quote :

"It is clear that intelligence is at least partly genetically determined. This was supported by the discovery in 2001 that the volume of the brain's grey matter, made up of "processor" cells, is heritable and correlates with certain elements of IQ (Nature Neuroscience, DOI: 10.1038/nn758). The amount of white matter, which provides the connections between these processors, has since been shown to be heritable too (Journal of Neuroscience, vol 26, p 10235)."

 

 

And also

 

"University of California, Los Angeles, scanned the brains of 23 sets of identical twins and the same number of fraternal twins, using a type of magnetic resonance imaging called HARDI. MRI scans typically show the volumes of different tissues in the brain by measuring the amount of water present. HARDI measures the amount of water that is diffusing through white matter, a measure of the integrity of myelin sheathing, and therefore the speed of nerve impulses. "It's like a picture of your mental speed," says Thompson.

 

By comparing brain maps of identical twins, which share the same genes, with fraternal twins, which share about half their genes, the team calculate that myelin integrity is genetically determined in many brain areas important for intelligence. This includes the corpus callosum, which integrates signals from the left and right sides of the body, and the parietal lobes, responsible for visual and spatial reasoning and logic (see above). Myelin quality in these areas was also correlated with scores on tests of abstract reasoning and overall intelligence"

 

With various indicators of intelligence being more closely correlated between identical twins than fraternal, it appears that intelligence is largely inherited, rather than being environmentally determined.

[Sayonara]

"At least partly" in the first excerpt and "correlated" in the second would seem to undermine the proposal "largely inherited". I would err on the side of "partly" and leave the magnitude of the effect for future studies to determine, personally.

 

I am sure that inherited traits are involved though.

[Paralith]

I have heard a wide variety of estimates of heritability for IQ; the highest has been 0.7, which is quite high, but remember: that still means that 30% of IQ is determined instead by environment. That's not too bad of a number. Other heritability estimates have it close to 0.5, in which case 50% is still determined by environment.

 

I think it's also important to keep in mind that while lots of traits thought to contribute to intelligence can be heritable, it's a whole other issue to quantify how much these traits actually DO contribute to intelligence, and to which aspects of intelligence.

[Mr Skeptic]

Yup, it does seem that intelligence has a large heritability component. A word of caution though: I've heard that having two smart parents increases your chance of autism. In any case, when you consider across species, intelligence is even more inheritable.

[Sisyphus]

That intelligence is at least partly inherited would be pointless to deny, as is the fact that it is not entirely inherited. Pretty much every study ever supports that very general statement, as does common sense. The reason there's no such agreement on the details is because "intelligence" itself is such a slippery concept, poorly defined and less well understood. Modelling it as some kind of substance that a mind can possess in greater or less quantities is tempting and has some uses, but ultimately is probably a poor representation for what is actually going on.

[DrP]

Slightly related, but relavant I believe... They say that anyone can achieve anything (unless your completey disables or retarded of course) if they put in 10,000 hours of practice. i.e. Person A who shows a particular talent for activity X will not be as good as Person B who has less talent for activity X but has put in over 10,000 hours of practice at it. So I agree with most of the above - I think you can inherit a certain amount of natural talent and intellagence, but to succeed and shine at anyting you need to make it your life and put in the hours (over 10,000) to be REALLY succesfull at it. A bit like the Tortoise and the Hare I suppose!

 

Here is a recent news link regarding the 10,000 hours (i.e. years of practice makes perfect): http://www.thisislondon.co.uk/standard/article-23588962-details/The+secret+of+your+success+10,000+hours/article.do

 

This link is better: http:// http://www.dailymail.co.uk/news/article-1078842/Practice-makes-perfect-Why-takes-10-000-hours-success-according-academic.html

Edited March 12, 2009 by DrP

[NowThatWeKnow]

Isn't "genetically determined" what makes evolution and natural selection possible? My observations tell me it plays a larger roll than many would think.

[Mr Skeptic]

Isn't "genetically determined" what makes evolution and natural selection possible? My observations tell me it plays a larger roll than many would think.

 

Yup, without the right genetics, we might have the intelligence of a gnat. However, all humans are not perfect clones, though genetically we are very similar. The differences in our individual genetics accounts for a good chunk of the difference between our individual intelligence -- but by no means all of it. Roughly half of the variation between two individual's intelligence is due to genetic differences between them, and the remainder to the details of their upbringing.

[Paralith]

Isn't "genetically determined" what makes evolution and natural selection possible? My observations tell me it plays a larger roll than many would think.

 

50% genetically determined is plenty for natural selection to work with.

[NowThatWeKnow]

...but by no means all of it. Roughly half of the variation between two individual's intelligence is due to genetic differences between them, and the remainder to the details of their upbringing.

 

Regardless of their upbringing, there are some that have trouble making it past Chimpanzee intellect. It is important to consider the difference in one's ability to learn and one's ease of learning. You may be capable of learning by rote or by understanding. Your upbringing my help determine what you know but changing your intelligence by 50% is stretching it IMO.

[Mokele]

Honestly, I just don't think we're anywhere near where we need to be to begin drawing real conclusions.

 

To be cynical, we're trying to estimate the heritability of a poorly-defined trait probably controlled by many, many genes and regulatory regions using fairly small sample sizes. No part of that is conducive to getting answers.

[SkepticLance]

One of the things that is, perhaps, a bit different about the study I quoted is that it is based on physical measurements, rather than dubious IQ tests. That is, the mass of brain cell, and wate rmovement within the brain. Both correlate closely with intelligence, and both measures are much closer in identical twins than in fraternal.

 

This method escapes the problems of interminably debating how accurate IQ tests are. While you could argue that the above measures are only indicative of intelligence, you cannot argue that what they measure is meaningless, since they are direct physical measurements. Good science!

[NowThatWeKnow]

This method escapes the problems of interminably debating how accurate IQ tests are. While you could argue that the above measures are only indicative of intelligence, you cannot argue that what they measure is meaningless, since they are direct physical measurements. Good science!

 

Good science would have gone well beyond using just twins. I would like to see a chart something like in the "Bell Curve" book.

[Sayonara]

One of the things that is, perhaps, a bit different about the study I quoted is that it is based on physical measurements, rather than dubious IQ tests. That is, the mass of brain cell, and wate rmovement within the brain. Both correlate closely with intelligence, and both measures are much closer in identical twins than in fraternal.

 

This method escapes the problems of interminably debating how accurate IQ tests are. While you could argue that the above measures are only indicative of intelligence, you cannot argue that what they measure is meaningless, since they are direct physical measurements. Good science!

Lance, look at what you are saying here. "The physical measurements correlate with intelligence". How was that level of intelligence established? Could it have been with... IQ tests?

[NowThatWeKnow]

Honestly, I just don't think we're anywhere near where we need to be to begin drawing real conclusions.

 

To be cynical, we're trying to estimate the heritability of a poorly-defined trait probably controlled by many, many genes and regulatory regions using fairly small sample sizes. No part of that is conducive to getting answers.

 

I present planet Earth as our laboratory. Watch a group of people in their original environment and then watch them over generations in the USA environment. The pecking order does not change.

[SkepticLance]

Sayonara said :

 

"Lance, look at what you are saying here. "The physical measurements correlate with intelligence". How was that level of intelligence established? Could it have been with... IQ tests?"

 

The truth is that the article did not specify. There are many ways of measuring intelligence, and they must all be correlated against each other to gain any meaning. IQ tests have a certain limited value. They do not seem to work when comparing people from different cultures, but have meaning when comparing people within one culture, and within the same socio-economic level.

 

I was also interested to note in another article I read some years ago, that IQ within one culture correlates closely with neuron impulse transmission speed. The article I quote in this thread also refers to this parameter. It may be that we need to develop better methods of measuring neuron impulse velocity and use that as a more objective measure. It would even have value across cultures!

[Paralith]

I won't deny that I have counted myself amongst IQ bashers for some time - but I recently read some more information on it which suggests that the scores are in fact fairly relevant to how we currently understand general intelligence (which in itself could be argued of course). When I have more time I'll try to look them up and link them here.

[Sisyphus]

Regardless of their upbringing, there are some that have trouble making it past Chimpanzee intellect. It is important to consider the difference in one's ability to learn and one's ease of learning. You may be capable of learning by rote or by understanding. Your upbringing my help determine what you know but changing your intelligence by 50% is stretching it IMO.

 

Accounting for 50% of variation is not the same thing as "changing your intelligence by 50%."

[arnolp04]

Not sure this really helps with the discussion but being something of a reductionist I approach any correlative research such as that featured in New Scientist with extreme caution. They remind me of epidemiological studies that try and link a cause to an effect, and so many of them fail to deliver the goods. And though this next comment might elicit a groan - IQ testing is far too limited in its scope to be a true measure of intelligence.

[NowThatWeKnow]

Accounting for 50% of variation is not the same thing as "changing your intelligence by 50%."

 

Point taken. My reply was also referencing post #9 "50% genetically determined is plenty for natural selection to work with." and my wording could have been different.