Skip to content
February 3, 2016 / JayMan

Rebutting Chanda Chisala

(This is also published at The Unz Review.)

Chanda Chisala has been producing pile after pile of nonsense for quite some time. At first, I was content with simply leaving comments at his posts refuting his rubbish because it was rather easy to point out where he was full of baloney. Since then, I’ve been banned by him, mostly for my signature flair. :)

I intended to continue to ignore his nonsense since it was such obvious rubbish that it didn’t seem to be worth my (now very precious) time. But then I realized the value of having nonsense essays picked apart for the nonsense they are. Rebuttals are highly valuable to skeptical readers who doubt nonsense but can’t quite put their finger on the problems themselves. So, in that service, I write this rebuttal to Chisala’s latest piece.

Towards a Theory of Everyone

Chisala’s theory is that different human groups differ in the degree of genetic canalization, and that explains the differences in average IQ between groups. It seems he lifted the concept of genetic canalization from Greg Cochran, who I’ll let describe the phenomenon. From Survival of the Flattest | West Hunter :

Genetic canalization is the extent to which an organism is buffered against the effects of mutations. Waddington said “developmental reactions, as they occur in organisms submitted to natural selection…are adjusted so as to bring about one definite end-result regardless of minor variations in conditions during the course of the reaction”. Canalization can act to buffer against environmental perturbations, and selection for resistance to such environmental noise may also produce resistance to genetic noise. But right now I’m thinking about genetic canalization.

Up to some point, the effects of not too many, not too serious mutations would be buffered: those mutations wouldn’t change the phenotype. In the same way, your typical tractor is not designed to nanometer tolerances: parts can be somewhat out of spec – up to some limit – without messing up performance.

Canalization is a product of natural selection. There would be stronger selection for efficient canalization in a species with more genetic load

It might explain why load doesn’t seem to have much effect on IQ over most of the range, why we haven’t seen general IQ depression in the children of old men.

So Chisala’s idea is that certain racial groups have greater levels of canalization, and that makes them more resistant to environmental stresses that might lower average IQ.

Oh God! Where to begin….

It’s hard for me tell if Chisala really believes what he’s saying. Because the truth of the matter is that he’s a bullshit artist, either wittingly or unwittingly. It appears that he has only a superficial understanding of the matters he discusses, and he tries to weave together cherry-picked pieces of information into a seemingly convincing story – at least for those who don’t know any better.

First of all, Chisala is claiming that there are no “genetic” group differences in IQ. Rather, every group has the same average IQ potential, but each group has a different level of canalization, thanks to natural selection (and this is not even genetic canalization – as in resistance to mutations – as Cochran discussed, but resistance to purported environmental insults). This makes each more or less resistant to the purportedly IQ-depressing effects of deprived environment. So first it’s not genetic, but it is? Which is it, man?

I don’t even want to imagine what reaction this particular proposition would garner if you ran it by this guy. —>

Second, Chisala seems to have no understanding of the concepts of elite samples, founder effects, measurement error, sampling bias, or of basic statistical principles like statistics of small numbers. That’s not even to mention his apparent lack of understanding of the breeder’s equation (but at least there he has plenty of company). He seems to be mystified by apparent incongruities he encounters in his cherry-picked (and often outdated) samples because of his ignorance of these important concepts and many other facts.

I’m not going to debunk Chisala’s claims point-by-point, because, really that’s not necessary (and his piece is much to confused to make that a worthwhile endeavor). Instead, I’m going to point out some key facts make his claims ridiculous.

One of those key facts is this:


There are global differences in brain size. Brain size is certainly related to intelligence, both on the individual level (Pietschnig et al 2015) and (even more so) on the group level (though the both the group level and individual level correlations are less than 1.0). In order for Chisala’s idea to work, these environmental insults must also cause certain racial group differences in brain size.

But, as we know, it’s not outside the realm of possibility that environmental insults can affect brain size (see the Zika virus). And sure, sub-Saharan Africa is loaded with pathogens and other environmental insults. But racial differences in brain size are seen between people of European, African, and Asian ancestry in the United States (from Rushton & Jensen, 2010):

Armed Forces Brain Size Rushton Jensen

(At this point, of course, we cue the sociologist’s fallacy invoking the poorer environments of Blacks even in the U.S.) But, Chisala is claiming Blacks are more susceptable to environmental insults that supposedly affect IQ – insults that (save perhaps iodine deficiency) have not been shown to actually impact IQ in any wayI’ll go into more detail in a future post, but there is little solid evidence for a negative impact of most supposed environmental insults on IQ.

For now, I’ll give you Greg Cochran on this (from The Great IQ Depression | West Hunter):

We hear that poverty can sap brainpower,  reduce frontal lobe function,  induce the  fantods, etc.  But exactly what do we mean by ‘poverty’?  If we’re talking about an absolute, rather than relative, standard of living,  most of the world today must be in poverty, as well as almost everyone who lived much before the present.  Most Chinese are poorer than the official US poverty level, right?  The US had fairly rapid economic growth until the last generation or so, so if you go very far back in time, almost everyone was poor, by modern standards. Even those who were considered rich at the time suffered from zero prenatal care, largely useless medicine, tabletless high schools,  and slow Internet connections.  They had to ride horses that had lousy acceleration and pooped all over the place.

In particular, if all this poverty-gives-you-emerods stuff is true, scholastic achievement should have collapsed in the Great Depression – and with the miracle of epigenetics, most of us should still be suffering those bad effects.

But somehow none of this seems to have gone through the formality of actually happening.

Of course, it’s also worth mentioning that brain structure differs detectably by race, as previously discussed:

a new paper, Fan et al 2015, that the details of cortical surface structure of the brain is highly predictive of genetic ancestry. Indeed, as Fan et al put it:

Here, we demonstrate that the three-dimensional geometry of cortical surface is highly predictive of individuals’ genetic ancestry in West Africa, Europe, East Asia, and America, even though their genetic background has been shaped by multiple waves of migratory and admixture events. The geometry of the cortical surface contains richer information about ancestry than the areal variability of the cortical surface, independent of total brain volumes. Besides explaining more ancestry variance than other brain imaging measurements, the 3D geometry of the cortical surface further characterizes distinct regional patterns in the folding and gyrification.

Indeed, an earlier paper from this team (Bakken, Dale, and Schork, 2011) found that this workswithin racial groups as well, as the case with Europeans (see also the section Intraracial Group Variation below):

In our group’s previous study, we found that area measures of cortical surface and total
brain volumes of individuals of European descent in the United States correlate significantly with their ancestral geographic locations in Europe

Then there is the work David Piffer on polygenetic score. Basically, the known genomic hits to IQ vary in frequency between the different populations highly according to average IQ. From Piffer 2015:

Published Genome Wide Association Studies (GWAS), reporting the presence of alleles exhibiting significant and replicable associations with IQ, are reviewed. The average between-population frequency (polygenic score) of nine alleles positively and significantly associated with intelligence is strongly correlated to country-level IQ (r = .91). Factor analysis of allele frequencies furthermore identified a metagene with a similar correlation to country IQ (r = .86). The majority of the alleles (seven out of nine) loaded positively on this metagene. Allele frequencies varied by continent in a way that corresponds with observed population differences in average phenotypic intelligence.

Here is a scatter plot from the paper:

Piffer polygene plot

Going even beyond this, if we follow Chisala’s logic and assume that somehow adverse reactions to the environment are responsible for the size, structural, and performance differences of African brains relative to other groups, then we have another problem: the performance difference between different human groups isn’t a 20th and 21st century phenomenon only – it goes back for the entirety of recorded history.

As we’ve seen before, and as Bryan Caplan recounts, the differences between human groups in development goes back thousands of years – such that level of development as far back as 1000 B.C. is predictive of development today. Indeed, as Easterly, Coming, and Gong (2007) recount:

We assemble a dataset on technology adoption in 1000 B.C., 0 A.D., and 1500 A.D. for the predecessors of today’s nation states. We find that this very old history of technology adoption is surprisingly significant for today’s national development outcomes. Although our strongest results are for 1500 A.D., we find that even technology as old as 1000 B.C. is associated with today’s outcomes in some plausible specifications.

It’s not like the poor performers and the strong performers of today are a new thing. They’ve been poor performers and strong performers throughout history (by and large). Indeed, in sub-Saharan Africa (emphasis mine):

Why this meandering reminiscence of mine about a random ruin in Turkey? Because sub-Saharan Africa has remarkably few ruins for its immense size.

This fact is not well known. It is so hazy in the contemporary mind that Henry Louis Gates managed to sell PBS on a six episode miniseries about African ruins called The Wonders of Africa without, apparently, anybody in PBS management calling his bluff about the lack of wonders that his camera crew would wind up documenting in one of the most boring documentary series of the 21st Century.

By contrast, as we know, there was plenty of development in East Asia and Europe, especially Northwestern Europe:




As Staffan put it, “we can’t adjust for their entire history.”

In any case, this recent nonsense idea of Chisala, aside from running afoul Occam’s Razor, is his attempt to undercut the rebuttal to the deprivation argument. That is, it is a common argument of blank slatists that poverty and other forms of deprivation are responsible for differences in average IQ and national performance. Aside from emptiness of the whole deprivation argument, as noted above, there is the fact (as pointed out by me in Welcome Readers from Portugal!) that outliers to this pattern of deprivation and IQ all perform in accordance to their measured IQ, not according to their level of deprivation. Poor rural Chinese perform nearly as well in IQ and scholastically as the other East Asian societies do. Citizens in wealthy Arab oil states perform as badly as those in poorer ones which lack oil. I’m sure Chisala doesn’t like this particular uncomfortable fact, so I suspect he concocted his feeble theory in part to try to nullify this unwelcome reality.

And finally, there is the fundamental problem that Chisala doesn’t understand either evolution or the formula that guides it, the breeder’s equation. There is no reason to suspect that human groups that have been separated for tens of thousands of years in vastly different environments would be the same in all their cognitive and behavioral qualities. In fact, a priori we should expect them not to be, since such equivalence after so many generations of separate evolution is nigh impossible.

I expected most of this to be obvious, which is why I haven’t paid too much attention to Chisala’s posts. But, I may have overestimated both his impact and people’s ability to spot the obvious, hence, this writing.

Commenters, please be aware of my comment policy.


December 24, 2015 / JayMan

The Chrismas Holiday

Look folks, I say “Merry Christmas” (and not “Happy Holidays”). And quite simply, here’s why:


Even though I am an atheist, the “Happy Holidays” euphemism is stupid.


November 26, 2015 / JayMan

Happy Thanksgiving 2015


Food for thought:


Passeth the cranb’rry sauce! The medieval origins of Thanksgiving

How and why did the dishes served at Thanksgiving dinner come to be so fixed?

Many assume that most of them were simply eaten by the Pilgrims during the first Thanksgiving. For this reason, they continue to be eaten today. And it’s true that most of the ingredients are American in origin: the turkey, cranberries, pumpkin, sweet potatoes – even the green beans in the casserole and the pecans in the pie.

Yet we only have one firsthand account of the “first” Thanksgiving – a brief paragraph by Edward Winslow that doesn’t mention any of these foods. And it’s been shown, time and again, that the idea of a unique culinary tradition originating from a feast between the Pilgrims and their Native American neighbors is more advertising myth than historical truth.

But maybe there is something, nonetheless, that’s very traditional about this meal.

In fact, there may be a very good reason these particular dishes – and even the way we eat the meal – came to be strongly associated with Thanksgiving. The first Americans simply mimicked or adapted the traditional fare, flavor combinations and rituals of Europe, using them to fashion the popular dishes we continue to enjoy today.

November 14, 2015 / JayMan

Terrorism Quotient

(This is also published at the Unz Review.)

(My reader poll results will have to wait, but rest assured, they’re coming.)

Yet another terrorist attack in Paris – this year:

I wish I could say I was even remotely surprised – perhaps only at the precise time, and that’s all.  For this is just another example of what I and so many others have been saying, as recently as the Cherlie Hebdo attack just in January.

Well, in this post, I’m here to straighten these people out on these things, as Bill Maher did in his interview with Brian Levin  after the Boston bombing – video does not allow embedding. Please visit the site:

The problem, ultimately, is this:

Green Map of Europe

The bulk of “terrorism” comes from one broad group of people: Muslims.

I know that that is partly a matter of definition:


But I want people to think of something. See this from my earlier post Guns & Violence, Again

Violence Map

Now see this (from Wikipedia):


The maps are pretty similar. The places on Earth with much interpersonal violence are generally also the places that larger-scale prolonged conflicts.

One might note that Muslim nations have fairly low rates of interpersonal homicide (assuming that these statistics are reliable, which is hardly guaranteed). This is partly because of the system of clan retribution, as Peter Frost explains here (The return of fear – emphasis mine)

Most Muslim immigrants come from societies where the State has pacified social relations only in recent times and where men still see violence as a legitimate and even necessary means to advance personal interests, to defend themselves and their families, and to acquire land, goods, and even women. Violence is constrained not by the State but by a balance of terror—the threat of retaliation by the victim or his kinsmen.

Hence, violence is Islamic societies quickly moves from being one-on-one (or one-on-a few or few-on-few) affairs as it is in many other places in the world to being protracted struggles between rival clans and tribes (featured at what is the MATTER with you people? | hbd chick):

What Muslim groups putatively lack in interpersonal violence, they more than make up for in prolonged mass conflict.

Despite these key facts, in response to this latest rampage in Paris, we have the usual nonsense, as representated by these Tweets:

In this post, allow me to introduce a very simple concept, as I will demonstrate with this Twitter exchange:

Let’s not forget this smart fellow here:

Perhaps what’s needed here is the idea of a terrorism quotient:

This is modeled after the “Amish Quotient” of Greg Cochran and Henry Harpending.

The idea is that there is a suite of behavioral traits that is more prevalent in many Muslim populations which makes them more likely to perpetrate acts of terrorism.

(Of course, every ethnic group has a group-typical suite of behavioral traits – an “quotient” – see Predictions on the Worldwide Distribution of Personality.

This is basic HBD.)

This is illustrated by the number of terrorist acts (defined here as instances of mass murder/assault/hostage taking) per capita for a given population. There is little question that this rate is incredibly high for many Muslim populations relative to other populations (and of course, there is a great deal of variation between Muslim populations) – even more so when you consider the sizes of the Muslim populations living in Western countries:

But the problem with Muslims in the West is hardly confined to terrorism, but plenty of regular old violence and other crime (especially in Europe – not so much in North America) – again from Peter Frost:

In France, Muslims make up 60% of all prison inmates, while being only 12% of the total population (Leclerc, 2014). Similarly, 7 out of 10 burglaries, assaults, and violent thefts are committed by first- or second-generation immigrants (Chevrier and Raufer, 2014). Most of these perps seem to be Muslim, although a third of them may be West Indians, Africans, and Roma of nominally Christian background. Muslims seem to be especially overrepresented in serious violent crimes that lead to prison sentences.

Similar trends are developing elsewhere. Muslims make up 70% all prison inmates in Spain and 45% in Belgium (WikiIslam, 2013 see Note 1;, 2013). In England and Wales, the figure is only 14%, versus 4.7% of the total population, apparently because certain other communities are likewise overrepresented (Morris, 2014, see Note 2).

A Danish researcher has studied the relationship between criminality and immigrant origin in Denmark, Norway, and Finland (Kirkegaard, 2014a; Kirkegaard, 2014b; Kirkegaard, 2014c; Kirkegaard and Fuerst, 2014). He found that the prevalence of Islam in the immigrants’ home country was the single best predictor of criminality both for “all crime” and for “violent crime,” being better than the home country’s mean IQ or GDP per capita and much better than its murder rate.

And let’s not forget Rotherham:

  • Report found 1,400 children abused between 1997 and 2013 in Rotherham
  • The figure is likely to be a conservative estimate of the true scale
  • Victims terrorised with guns and doused in petrol and threatened with fire
  • More than a third of the cases were already know to agencies
  • Author of the report condemned ‘blatant’ failings by council’s leadership
  • Action blocked by political correctness as staff ‘feared appearing racist’
  • Majority of victims described the perpetrators as ‘Asian’ [overwhelmingly Pakistani] men
  • Leader of Rotherham Council has stepped down with immediate effect
  • No council employees will receive disciplinary action, leaders state

This illustrates that the typical WEIRDO response to these crimes – such as pointing out (correctly) that only a small fraction of all Muslims commit these crimes, as true as that is, misses the point.

What’s more there is no reason to have large populations of Muslims in Northwestern European countries. It’s one thing when a group has a historic presence in a place, like American Blacks or the long-term Mexican residents of El Norte in the U.S. do. The country is as much theirs as it is that of the Whites living there. But the Muslim populations in Europe are overwhelmingly recent immigrants.

At the very least, one would imagine that it would be prudent to stop admitting more Muslims into these countries. As much as I am loathe to quote Ann Coulter:

But there’s a good chance that that won’t happen. Much of what I say here – meant to jar Northwestern Europeans into prudent action to protect their societies – may end up falling on deaf ears. The reason why is explained by the very same HBD that explains why Muslims are so much more violent, on average – namely, Northwestern European universalism:

Nobel-Muslim Plot

As we saw previously in my posts Clannishness – the Series: Zigzag Lightning in the Brain, there is a strong correlation between the size of the Muslim fraction in European countries and their scientific (and other intellectual) performance. A suite of behavioral traits found principally in Northwest Europeans – regard for all humanity, generosity, high-trust, the absence of kin-based social bonds –  leads them to accept clannish migrants. See The Rise of Universalism:

childlabormap Womens-right-around-the-world

Worse still, NW Europeans accept immigrants from the most incompatible corner of the world, the Muslim/Arab world:

In many respects, Muslim groups (especially Arab ones) are the polar opposites of Northwest Europeans. Northwestern European society is liberal, democratic, individualistic, secular, and high-trust. Arab society is illiberal, autocratic, collectivist, extremely religious, and low-trust. Social bonds in Northwestern European societies are primarily among non-relatives (at least past the nuclear family). Social bonds in Arab society are structured around kin. Institutions in NW European societies are rule-bound. Institutions in Arab societies are corrupt.

Corruption 2014

This is genetic in origin, the product of evolution.

For more, see these two key posts by HBD Chick:

big summary post on the hajnal line | hbd chick

community vs. communism | hbd chick

Because the differences between these groups of people is inherited, the result of centuries of natural selection in their respective environments, these features can’t be expected to change much. Northwestern Europeans and Arabs (and many other Muslim groups) are, as groups, largely incompatible. Social strife emerges when they are brought together as they are in modern Northwestern European countries.

To illustrate that Northwestern European universalism is responsible for the settling of large numbers of Muslims in Europe, note what you don’t see:

Unfortunately, the very HBD that leads to these differences also makes it hard for Northwestern Europeans to see the folly in their immigration policies. In reaction to events like the Paris attacks, we get this:

As discussed by M.G. over at Those Who Can See: Reacting to Spree Killings, Progressively

Oh, and for the New Atheists out there that like to blame Muslim violence on their religion, it’s worth noting that the behaviors we associate with religion – including the religion itself – are all heritable:

The Atheist Narrative 

Religion comes to the religious because that’s how their brains are wired. A believer cannot think any different … Believers literally have God/Earth spirits/Buddha on the brain. To such a person, their deities are as real as the Sun in the sky (since, after all, the believer’s brain is the only brain he’s got). Religiosity is highly heritable (as are all behavioral traits)…

This indicates that religious belief – or lack there of – is largely intractable. It is a futile effort to get people to give up religion en masse (or, for that matter, to get non-believers to believe). You may have some individual “successes”, largely because of changing the environmental context of people who already had the genetic potentialfor whatever belief you want to instill, but you’re not going to achieve broad change in the population.

However, the “New Atheists” don’t seem to see it that way. Many of these speakers, including the likes of Richard Dawkins, or groups such as American Atheistsproselytize atheism. Indeed, Dawkins, a self-described “militant atheist”, is very much an atheist evangelist.

The belief that these individuals’ actions appear to be based is that by spreading atheism and getting people to give up their religious beliefs, society can be improved.

As I have previous written, that is a foolhardy goal. The unsavory traits the New Atheists seek to change stem not from the religion, but from the people. Indeed, in the spirit of what HBD Chick would ask, where do religious beliefs come from? Sorry atheist zealots, you can’t get Muslims to behave like modern civilized (Northwestern European) people by getting them to give up Islam. You can’t turn the U.S. Deep South and Greater Appalachia into Yankeedom or the Midlandsby getting the former two to give up fundamentalist Christianity.

So what to do, then? First and foremost, especially for Northwestern European countries, is to stop admitting Muslims en masse into Europe.

 (It’s worth mentioning that the problem is much more acute for Europe than it is for NW European diaspora nations like the U.S. or Canada. Put simply, the Atlantic Ocean is a bigger barrier than the Mediterranean Sea. Europe gets a much more representative slice of the Muslim population. By contrast, immigrants to North America tend to be more select because of the demands of making the trip. Hence, here in the States we get higher IQ, less clannish Muslims. Of course, that’s not all that rosy – a smart terrorist is a much more dangerous thing than a stupid terrorist. But North American Muslims don’t have the incredibly high crime and poverty rates European Muslims do.)

At the very earnest, any attempts to address the problem should start with not making it worse. Even more troublesome, a loose, porous border allows radicalized Muslims to travel freely from terror hotspots in the Middle East to Western sites. France’s emergency reaction to close it’s border was the right step (but, on cue, there are calls for France to open its border once again –Why France Should Not Close Its Borders). Cutting the number of “refugees” granted asylum in Western nations would be next. (Most of whom are economic migrants anyway.)

That addressed new Muslims in the country, but what about the existing populations? I for one do not advocate mass deportations, nor do we need encourage Westerners to engage in mass persecution of their Muslim populations. That said, some steps can be taken to tackle the issue. For example:

  • Disallow entry for families of Muslim immigrants
  • Deport any immigrant convicted of a crime

Now, that said, for France – with it’s very high Muslim population and it’s much higher Muslim share of births in the country – there doesn’t seem to be an easy remedy. They’re in a hard position – and worst of all, they don’t even realize it, generally.

Unfortunately, I don’t see this matter headed to good places, neither for Europeans or for the Muslims and other foreigners that live in Europe. That last thing we need is to inspire backlash against the Muslim residents by the natives. One hopes that steps to address this issue in an orderly and humane way can be taken, but I have to admit, that’s just a hope.

November 2, 2015 / JayMan

Reader Poll 2015 – Let Me Hear From You!

(This is also published at But feel free to take the poll here, it all goes to the same place. ;) Leave any actual blog comments to this post over at, please.)

I want to take the temperature of the room, so to speak. Here’s your chance to let me hear from you. I encourage all readers to participate, including the occasional drifters, lurkers, etc. The more people participate, the more accurate the results will be. Please chime in!

Results will be published in one week.

Questions marked with a red asterisk * are required. All the text boxes are (or should be, at least) optional

October 31, 2015 / JayMan

This Halloween…

You don’t know the power…

Vader Latern

On that, here’s a duel we’ve been waiting to see:


October 21, 2015 / JayMan

Regression to the Mean

(This is also published at The Unz Review.)

It seems few understand regression to the mean and how and why it works.

Most people (and by most people, I mean most scholars – i.e., the people who should know better) have a vague understanding that it has something to do with IQ. They seem to have the impression it means that the children of smart parents will be less smart. Even more so when those parents come from a population with a low mean IQ.

And they seem to think this phenomenon goes on forever, such that grandchildren and great-grandchildren continue this march to mediocrity.

Well, a lot of this is confused to plain old wrong.

Let’s start with what regression to the mean is. Above is an illustration of a bell curve. A set of parents that lie out on the curve away from the mean will indeed tend to have children that are closer to the average. Hence, if a set of parents are  +2 standard deviations for a trait, their children will be typically some degree closer to the mean.

The first thing to clear up is that regression to the mean operates in both directions. Just as parents +2σ will have children some degree less far off to the right on the curve, parents –2σ will have children some degree less far off to the left. That is, children of parents who are below average for a trait regress up.

To clear up some additional confusion, let’s look at what causes regression to the mean. The root of the phenomenon goes back to behavioral genetics, or more broadly heritability. Human traits have several components that contribute to trait variance. They are:

A: Additive heredity
D: Non-additive heredity (D from “dominance”)
C: Shared environment (C from “common environment”)
E: “Unshared” or “unique” environment.

As we’ve seen before, we know that A is typically 50-60%, D 10-20%, C is 0%, and E the remaining 20-30%.

The key fact is that for the transmission of a trait from parent to child, only A and C carry over to the next generation. But, as we know, C is 0; so that only leaves A. The rest, including non-additive heredity (which is basically fortuitous combinations of alleles) and whatever remaining “non-genetic” factors that constitute E (and all the things that comprise that, see Environmental Hereditarianism) are essentially luck. And since we can’t expect lightning to strike twice (as improper as that metaphor is), regression to the mean happens because luck goes away.

This is governed by the breeder’s equation.

R = h2 S.

R is the response to selection, S is the selection differential, and h2 is the narrow-sense heritability. This is the workhorse equation for quantitative genetics. The selective differential S, is the difference between the population mean and the mean of the parental population (some subset of the total population).

This equation can be used in different ways depending on whether we’re talking about whole populations or individual pairs of parents (though fundamentally for the same reason).

Let’s start with individuals. If two parents (let’s say White Americans) are +2σ for a trait, let’s say IQ, or 130,  and we give the additive heritability of IQ to be about 0.6, we can expect their children to collectively have an average IQ of

0.6 • +2 = +1.2σ

…or 118. Now, this was assuming that their families had a mean IQ of 100. If their families had a different mean IQ, lets say 120 (+1.333σ), the breeder’s equation would give

0.6 • (2 – 1.333)σ = +0.6667σ

…or a mean IQ of 125 for the children. (That’s because it’s +0.6667σ plus the family mean IQ of +1.333σ.)

What’s better, here’s another illustration. Let’s say the parents’ families have a mean IQ of 120, but the parents themselves have IQs of 110. Given the breeder’s equation,

0.6 • (+0.6667 – 1.333)σ = –0.6667σ

…for a mean IQ of 114 for their children (family mean IQ of +1.333σ minus 0.6667σ). In other words, even though the parents (with IQs of 110) are above the mean of the population, because their families are well above average, their children regress up.

It’s important to make clear that the breeder’s equation, and hence regression to mean, works the same way for any quantitative trait, not just IQ. This includes political orientation, height, body weight, personality, etc. All you need to know are the values to fit the variables in the equation.

For populations, the equation works similarly. Hence, if a group of people with a mean IQ of 130 (who come from population with a mean IQ of 100) go off somewhere and have children, the next generation will have a mean IQ of 118. Now here’s the part that gives a lot of people trouble: the children of the children of this group, the third generation, will also have a mean IQ of 118. Why? Because the initial event changed the mean. The new “population mean”, as far as the breeder’s equation is concerned, is 118. As long as they mate endogamously, there will be no change in their average IQ thanks to regression (only through selection).

This is should illustrate the flaw in thinking that regression happens forever. If daughter populations regressed back to the mean of their original source populations indefinitely, how could there be any selection for quantitative traits? Think about it.

Now let’s return to individuals. Some think OK, if populations don’t regress forever, surely the descendants of any one pair of parents do, yes? Well, not necessarily. Let’s return to our example of the offspring of IQ 130 parents from mean IQ 120 families. When it comes time for their children (the second generation), with a mean IQ 125, to have children, we do again run the breeder’s equation. But the key fact here is that the mean value the third generation of children are regressing to is the mean of their respective families. If all of the 2nd generation parents mated with spouses from high mean IQ families, there would be little to no regression for the third. In other words, regression to the mean for individuals can be slowed or halted by assortative mating. This is why wealthy parents have concerned themselves with the family backgrounds of their children’s mates. And this is why Gregory Clark found what he found (see The Son Also Rises | West Hunter) – namely, very slow regression (around 10 generations, in many cases) to the population mean for families (indeed, virtually none in Indian castes, who only mate within caste).

Indeed, as I mentioned, the reason for regression is the same for individuals and populations. You see regression in populations because the exceptional individuals who comprise whatever select group in question are going to be coming from families of all different averages for whatever trait under consideration. The sum of all these individual regressions is going to add up to regression towards the mean of the source population. (But as mentioned before, this only happens once.)

Hopefully, this serves to clear up the confusion on regression to the mean.

Clever people might notice that all of HBD is based on just two concepts: behavioral genetics (or again, more broadly, heritability) and the breeder’s equation. Know those two things and most of the rest follows.


Get every new post delivered to your Inbox.

Join 2,003 other followers