Why does IQ cluster around 100 points?

[rousseau]

So it's possible that all of the issues we see with people and strange beliefs is a feature, not a bug, of our species.

This was actually the most interesting point, to me, in the OP.

Odd beliefs and cultural customs are innate and an imperative of our psychology.

 

[Jokodo]

Well, here is what Wikipedia has to say anyway.

"When controlling for education and socioeconomic status, the relationship between intelligence and number of children, intelligence and number of siblings, and intelligence and ideal number of children reduces to statistical insignificance" - your link.

' In considering these results along with those from earlier researchers, Vining wrote that "in periods of rising birth rates, persons with higher intelligence tend to have fertility equal to, if not exceeding, that of the population as a whole,"' - also your link.

In other words, it's not that intelligence is negatively selected for, but that subpopulations of lower socio-economic status (which correlates with lower IQ, though to which degree this is a genotypic rather than merely phenotypic effect is highly debatable) are slightly lagging behind in the society-wide trend of declining fertility.

- - - Updated - - -

So it's possible that all of the issues we see with people and strange beliefs is a feature, not a bug, of our species.

This was actually the most interesting point, to me, in the OP.

Odd beliefs and cultural customs are innate and an imperative of our psychology.

You need to read more Stephen J. Gould!

 

[rousseau]

"When controlling for education and socioeconomic status, the relationship between intelligence and number of children, intelligence and number of siblings, and intelligence and ideal number of children reduces to statistical insignificance" - your link.

' In considering these results along with those from earlier researchers, Vining wrote that "in periods of rising birth rates, persons with higher intelligence tend to have fertility equal to, if not exceeding, that of the population as a whole,"' - also your link.

In other words, it's not that intelligence is negatively selected for, but that subpopulations of lower socio-economic status (which correlates with lower IQ, though to which degree this is a genotypic rather than merely phenotypic effect is highly debatable) are slightly lagging behind in the society-wide trend of declining fertility.

Yea it sounds like some of the evidence doesn't make the issue completely clear. I didn't reply to your post above because I think some of your comments are off-base, but I don't want to spend the time trying to convince you, so we can agree to disagree.

 

[AirPoh]

I've been running through some ideas lately about why the IQ of most populations clusters around 100. It seems strange to me that if intelligence, reason, and problem solving skill are generally considered positive traits, why the population doesn't drift to the right. Instead it seems like there is some kind of reproductive advantage of not being too smart.

But to take it a bit further I've been asking myself: well, what is a person like that's not too smart? Some thoughts:

- They're more likely to take social norms for granted
- They're less likely to question ideologies that act as social bonds
- They may be worse at family planning so reproduce more at the expense of their future
- High IQ might come at the expense of EQ, which is more critical to forming relationships

It's an interesting point to consider because it suggests that, in some ways, intelligence can be maladaptive. So it's possible that all of the issues we see with people and strange beliefs is a feature, not a bug, of our species.

Your thoughts?

The IQ of individuals vs the reproductive advantage of a population is not a valid comparison. As far as the clustering, it's a typical bell curve. The value 100 was arbitrarily assigned.

 

[Kharakov]

I'm still pissed that the online IQ tests doc you 50 points if you pay for analysis of the results.

 

[bilby]

Can you make your reasoning here a wee bit more explicit?

If intelligence is heritable, which it is, and 68% of the population has an IQ between 85 and 115, and this proportion is relatively stable, this means that people in that range are producing children at a much greater rate than people with a significantly lower IQ or a significantly higher one. And if intelligence was completely arbitrary we wouldn't see a distribution at all, it would be random.

From that it follows that there is very little, to no discernible reproductive advantage of having an IQ above 115, as opposed to one between 85 and 115.

You could argue that the distribution is shifting right, and it possibly is, but theoretically there has to be an upper limit, intelligence can't increase infinitely.

The mere existence of an upper limit is no indication that we are anywhere close to it.

In the early 1800s, it was believed that the upper limit for vehicle speed was around 20 mph, as humans could not survive greater speeds. Later in that century, people were concerned that at speeds approaching 50 mph, air would be sucked from a railway carriage, and the occupants would asphyxiate.

Those limits were based on nonsense, of course. But the idea that the speed of sound was a hard limit for vehicle speed was based on sound (pun intended) engineering principles in an atmosphere. Yet supersonic flight became a reality in the middle of the 20th century. And the actual hard limit on speed is lightspeed, per Einstein - those mid twentieth century engineers with their 'limit' at Mach 1 were waaaay below the hard limit imposed by uncle Albert.

The point being that we may accept that intelligence is theoretically limited; But there's no reason at all to imagine that we are even 1% of the way to that limit.

Being intelligent might be selected for. It's got a genetic component, but it's not purely a function of genetics, and there's good reason to think that much of the recent observed increase is due to other factors.

Essentially, we don't know; All of your foundational assumptions in the OP are doubtful at best, and totally wrong at worst (eg. as others have pointed out, average IQ is defined to be 100 for a given population, so it cannot be otherwise).

There are some interesting questions here; But you need to tidy up your assumptions before you can get to them. The OP is trying to run before it can walk.

 

[Kharakov]

Can you make your reasoning here a wee bit more explicit?

I'm still trying to figure out how most of it (IQ) clusters in my head. Might be my blind spot.

 

[Speakpigeon]

EDIT
Hey, I think I'm the only one here to have replied with something more than a derail! Yes?

The OP is a derail, replying with anything other than a derail is off topic.

The failure to understand what people may mean from the confused way they say it should be taken as a possible symptom of something you might want to worry about.

Still, I had a good laugh. Thanks.
EB

 

[Speakpigeon]

I'm still trying to figure out how most of it (IQ) clusters in my head. Might be my blind spot.

Beware, IQ isn't a measure of how bright you are.

The people who invented IQ tests made sure they were themselves in the range above 100. So, there's a bias anyway here.

And that was also a long time ago. Now, these people would be around or below 100. Who wants to have his IQ assessed by a test designed by people with a low IQ?

Show

And now, let's see what people with a low IQ think of that.

EB

 

[Speakpigeon]

The point being that we may accept that intelligence is theoretically limited; But there's no reason at all to imagine that we are even 1% of the way to that limit.

Well, having a low IQ and having a high IQ both are reasons to want to believe there's a limit to IQs.

I think myself the sky is the limit.

All I can see around me looks like clouds to me. What does that mean, I wonder? (I'm not asking what you think, though.)

I think the sky is the limit but that there's a limit nonetheless. However, there is no limit to the ratio between this limit and our own IQs. Current IQs may be like 0.5 to 1, or like 0.1, or like 0.01, or indeed like 0.00000000000000001 to 1.

Oh, sucks!
EB

EDIT
Only UM KNOWS there's a limit! The infinitesimal cannot possibly exist!!! LowIQED.

 

[rousseau]

EDIT
Hey, I think I'm the only one here to have replied with something more than a derail! Yes?

The OP is a derail, replying with anything other than a derail is off topic.

The failure to understand what people may mean from the confused way they say it should be taken as a possible symptom of something you might want to worry about.

Still, I had a good laugh. Thanks.
EB

I tend to have a problem with being a few steps ahead of other people and assuming their understanding, but ending up confusing them. But in this case I can't tell whether or not I'm the one who's not understanding

In either case going forward Google Scholar is my friend.

 

[Speakpigeon]

The failure to understand what people may mean from the confused way they say it should be taken as a possible symptom of something you might want to worry about.

Still, I had a good laugh. Thanks.
EB

I tend to have a problem with being a few steps ahead of other people and assuming their understanding, but ending up confusing them. But in this case I can't tell whether or not I'm the one who's not understanding

In either case going forward Google Scholar is my friend.

God bless your soul, we're all very confused beings deep down. It's just that for some, the confusion starts not too deep. I can't give names. I'm already on short notice.

Show

Is it possible Google Scholar may be some imaginary friend you have?

EB

 

[J842P]

I'm still trying to figure out how most of it (IQ) clusters in my head. Might be my blind spot.

Beware, IQ isn't a measure of how bright you are.

The people who invented IQ tests made sure they were themselves in the range above 100. So, there's a bias anyway here.

And that was also a long time ago. Now, these people would be around or below 100. Who wants to have his IQ assessed by a test designed by people with a low IQ?

Show

And now, let's see what people with a low IQ think of that.

EB

You realize that the test has changed dramatically since it was invented by a series of scholars not related to the original inventors, right?

 

[barbos]

Are you asking why IQ has a normal distribution?

Also, the idea that high IQ is maladaptive is certainly not new, and I think it is pretty reasonable and compelling.

The very high IQ people I know don't tend to be biologically fit.

Overall IQ, however, has been increasing dramatically. That is to say, someone who had an IQ of 100 in 1920 would probably score around an 80 now. This effect is way too fast to be explained by selection, likely, it is due to things like overall improved nutrition and a world that exercises the things that IQ measures more than the world of the average person from the 18th/19th century.

In any event, I would be careful of inferring too much from the shape of the distribution statically. A trait could be highly adaptive or maladaptive but the trait can still be normally distributed in a population at a given time. Especially a trait like IQ, which would be a classic example of continuous variation.

The question isn't mathematical, the question is what reproductive advantage is there to people who fall within the average of the IQ distribution. Not is there an advantage, but what specifically is the advantage.

Advantage is that you are not being labeled too smart. by the most of the people

 

[Kharakov]

I'm still trying to figure out how most of it (IQ) clusters in my head. Might be my blind spot.

Beware, IQ isn't a measure of how bright you are.

Is that a lumen pun? I've never seen one of those before.

 

[Speakpigeon]

I'm still trying to figure out how most of it (IQ) clusters in my head. Might be my blind spot.

Beware, IQ isn't a measure of how bright you are.

Is that a lumen pun? I've never seen one of those before.

Too damn dark in there?
EB

 

[Speakpigeon]

I'm still trying to figure out how most of it (IQ) clusters in my head. Might be my blind spot.

Beware, IQ isn't a measure of how bright you are.

The people who invented IQ tests made sure they were themselves in the range above 100. So, there's a bias anyway here.

And that was also a long time ago. Now, these people would be around or below 100. Who wants to have his IQ assessed by a test designed by people with a low IQ?

Show

And now, let's see what people with a low IQ think of that.

EB

You realize that the test has changed dramatically since it was invented by a series of scholars not related to the original inventors, right?

Your word "dramatically" is the only thing dramatic here.

I'm sure an IQ test measures something. The question is what exactly. Yet, IQ does mean "intelligence" quotient. How would they know?

Accepting your intelligence is measured by an IQ test seems to be a sign of low intelligence to me. And indeed, many people who score high enough will idiotically take the IQ test as defining what intelligence is.

The reality is that none of us could really say what intelligence is, not even close, let alone how to measure it. Again, IQ tests measure something but so do all school and university tests, and indeed all tests involving mental capabilities.

I will guess that saying that an IQ test measures intelligence is like saying length is a measure of volume. A measure, yes, but not of volume. Unless of course, you redefine volume as what is measured by length.

You realise that, right?
EB

 

[Speakpigeon]

The question isn't mathematical, the question is what reproductive advantage is there to people who fall within the average of the IQ distribution. Not is there an advantage, but what specifically is the advantage.

Ah, here my IQ is so high I could identify your mistake. Are you ready for it?

People who fall as you say within the average of the IQ distribution do not necessarily make a population apart from those who fall outside. They may reproduce with people outside the range. Their offspring may spread across the spectrum. Many people marry outside their category just because criteria for selecting a reproduction partner are themselves extremely varied. Many men may choose a dumb woman and many women may elect to appear dumb or indeed just act dumb because of their emotional or hormonal state.

There seems to be no reason to assume an advantage to being in the average, unlike for example the tendency to be gregarious if you're not a predator. Intelligence is not a trait which is easily identifiable. Many intelligent people will adopt a low profile if they feel it's in their interest, for whatever reason, including that of avoiding being conspicuously more intelligent than their neighbour, especially if it's a Nazi sympathiser.

People may not want to advertise their intelligence except perhaps in modern times, where the state may come to find useful to select an elite of intelligent people, perhaps for example through higher education, and where finding a job and a better pay can sometimes depends on how smart your are. Yet, even there, it may well be that many intelligent people will just prefer to stay out of that elite. Intelligent people presumably have emotions and emotions may be more predictive of what people do in life. Unless IQ tests are biased against emotional people, as I think they are.

And it's not a sign of intelligence to insist on wearing your better intelligence on your sleeve, including in business.

On the other side, many idiots may be intelligent enough to make sure they appear more intelligent than they are. I'm not even convinced we're too good at judging intelligence in others. There are too many social, cultural, ethnic, gender-based prejudices to skew your judgement.

You would have a point if intelligence was somehow correlated with any number of pathologies, deficiencies, inadaptations etc., and then only if those had an effect on the ability to reproduce. Many famously bright people were also epileptic, for example. Well, apparently they still managed to do well enough to become famous to begin with, like Julius Caesar for instance.

I think the mistake is to conceive of the population in the average range as a kind of huddled mass of people living and reproducing together, and people on the outside of the range as isolated and maladjusted individuals with a red mark on their forehead saying "Loonie, Beware". The reality seems to be that there are all sort of reproductive strategies, and more importantly, that those strategies trump any rational strategy to select your partner on the basis mainly similarity of intelligence. This in my view prevent each group from constituting a population appart from the rest.

Well, I'm running out of arguments here. I hope this will be enough to convince you.
EB

 

[rousseau]

The point being that we may accept that intelligence is theoretically limited; But there's no reason at all to imagine that we are even 1% of the way to that limit.

I couldn't point you to anything that proves this empirically, but to me the shape of the curve as well as the raw physics of genetics suggests that there is a very real, hard limit.

- IQ measures problem solving ability, and at some point the real, material problems of the world don't require more fire-power, and instead one could argue that many jobs have as much of a social component as they do a problem solving one. Consider a person with an average IQ, and a normal temperament, vs another with an IQ of 160 who is completely socially maladjusted (I saw a couple of these people in college). In terms of life outcomes the person with an average IQ will have more career and reproductive success, because they can talk to people and build a network.

- Genetically, problem solving skill and the resulting bell curve should be a product of genotypic variation, but the average real, problem solving skill (aka 100 points) isn't actually very high, and as we get closer to genius levels the curve tapers off dramatically. There isn't even a slow decline, 70 out of every 100 people have essentially the same ok problem solving skill, and then there is everyone else. That the average landed in this range can't be arbitrary, there has to be a reason why more people landed at that level as opposed to others. I'll grant you the whole curve can shift, but because of the dramatic tapering of the curve I suspect that one can have excessive problem solving ability, in the same way one could have excessive height. Human characteristics can't grow infinitely, and I don't see a reason why problem solving ability should be any different. On some level this might be a biological limit.

And actually I think some parts of what I've written above might be close to an answer - if life provided challenges that meant only people with a 140 IQ could survive, then the curve would shift dramatically to the right. But maybe it's that the challenges that are inherent to being a person in the world mostly require a brain with an IQ hovering around 100, along with other well adjusted components.

God I need to take a break from this forum.

 

[Loren Pechtel]

Brains are costly to run. The more intelligence the more it costs to run the brain. There's a point at which you don't get enough benefit from the extra intelligence to pay the cost of running the additional brain. Hence evolution limits intelligence.