But it's unlikely we'll make any advancements in our understanding of genes and intelligence or behavior, because this kind of research is out-of-favor and almost impossible to fund now.
The premise of those studies is linear additive effects from each causal factor, which is almost certainly false; and in general, there is no way of establishing causation without interventional experiments. If the effects were plausibly non-linear, we would need 1 trillion+ data points even to establish statistically significant differences.
These fields are all cargo-cult stats, putting data into GUIs and printing pro-forma reports. The people involved are in way over their heads, to the degree that there isnt anything to "reproduce" let alone try to reproduce the experiments: they dont have any.
The whole thing is little more than principle component analysis on astrological star data.
When and where we are born definitely has an effect on personality, irrespective of family, in most cases. Astrological star data is a proxy for the when and where, and while thus would not be causative, would often be correlative. So it makes sense to do PCA on it as you'll identify a lot of good correlations.
So in the case of astrological analysis we would, if we wished to change population personalities change, say where people were born -- in the case of psychometrics we're told that we have no control over the causes whatsoever (genes).
In the vast vast majority of observational genetic studies genes are just proxies, in the the same way the star signs are. In other cases, they're mere correlations.
In the case of IQ (and basically all social genetic studies) it is highly likely that any correlated genes are merely proxies for geographic-historical distributions of peoples over time and it was the long-time-scale geographic and historical effects (culture, education, wealth, famine, poverty, war...) that we see in attainment.
(Setting aside that IQ tests aren't valid above average IQ and have extremely bad properties both at the individual and population level for most of the measured range. )
To say that "genes cause IQ" is several levels of confusion. The claim has nothing to do with whether genes determine the physiological body structure, the claim is whether relevant aspects of human intelligence are a product of the at-birth or developmental structure -- or of that acquired from the environemnt, ie., neural plasticity / brain structure / etc.
Almost all evidence we have is that relevant aspects of human intelligence are environmental, ie., acquired. There is little evidence of the alternative because the experiments needed to establish it are large impossible or unethical. So it might be true, but we have no evidence of it.
Insofar as any claims are made about genes and IQ they amount to associating markers of geographical-historical migration (ie., breeding across time) with a very bad proxy measure of abstract reasoning which, at best, only detects deficits with any reliabiliy.
So we have proxies on top of correlations on top of terrible measures of anything with zero reliability in the range of interest. This whole thing is operating nearly at fraudulent levels of "research".
There's very very little this field can say scientifically, since there arent any experiments. It's all pseudoscientific uses of stats.
To simplify matters, suppose that we know for sure that all above-average differences in IQ are 100% environmental/acquired-during-lifetime. Now, so what do twin studies show, on this assumption?
They show that genes must be correlating with these environmental measures, and twin studies give us an 'effect size' for geographical-historical patterns of reporduction.
So twin studies, even if they were valid (and their assumption of linearity renders them invalid), do not decide the matter. You need indpednent evidence of causal mechanisms from experiments, which doesnt exist.
Are you sure about that? If I find someone that we all agree is “pretty damn smart” and they regularly score 115+ and we find someone that we all agree is “not very smart at all” and they regularly score < 90. And we repeat that dozens of times, it seems like the IQ test is a measure of intelligence.
It may be imperfect, and pretty clearly does not have three significant digits of precision, but it seems it’s still a measure of the thing we’re trying to estimate, same as a set of mixed stones and a playground seesaw can provide a comparative measure of weight.
But all attempts to do this, i'm aware of, show in fact IQ tests don't behave this way. That all correlation with objective measures of performs, with reliable measures, end up random >100 -- and weakly non-random <100.
So what we, in fact find, is that IQ tests only reliably correlate in the 'mental retardation' region of performance.
There is, possibly, a sort of non-objective culturally feeling to the kinds of people who might do well on IQ tests. Call these personalities, "puzzler bureaucrats" it isnt clear that even for people in this population we're percing any sort of objective intelligence-related performance.
Eg., suppose we had an objective measure of intelligence based on a deep causal model of the brain and how it interacts with body/environment. Suppose we found out that a population who score 100-110 on IQ tests were vastly more intelligent than another scoring 120-130.
Now, could we find independent measures of performance to substantiate that? Yes, trivially. Take, eg., a group of CEOs and a group of maths undergrads. The former, could by supposition, have a much higher performance on a variety of objective measures.
Even assuming we agree that that’s the only usefulness of an IQ test, in what way does that make them not a measure of intelligence?
A ruler is still a measure of length even if it can’t measure the size of an atom or the distance to the moon.
this is no way to establish validity or reliability. you need an independent theory of intelligence and a variety of indepenent objective measures -- otherwise the whole enterprise is circular
> you need an independent theory of intelligence
Sure. We have some of these. Despite it's flaws and limitations I'm partial to portions of Guilford's Structure of Intellect.
> and a variety of indepenent objective measures
The various sub-tests in an IQ test are nominally independent, yes? Going back to your "CEOs", I don't see how a social position can be assumed to be objective when it is subjectively contingent on external social processes.
The experiment raising an infant chimpanzee alongside a human infant has been done. To presuppose that human intelligent is categorically distinct from chimpanzee intelligence such that this experiment does not lend evidence to a genetic basis of variations in human intelligence is further than I would go.
I presume that some amounts of variation in intelligence, as well as IQ scores, is due to factors that are neither directly genetic nor environmental, but are more random (such as cell division and post-fertilization DNA replication and rearrangements).
I don't understand this. Why would you need linear additive effects to think that if identical twins are more similar than fraternal twins and half siblings are less similar than full siblings along some axis then there is probably a genetic component?
Do you have a credible source for this claim? The criticism I'm seeing is largely constrained [1].
Like, if it was determined tomorrow, with a huge article in nature or another journal that's suitably popular/prestigious that intelligence (and rewards for the sake of this thread) is totally inherited or even 80% inherited, what material changes would you want/expect to see in society in relation to that news.
This has a real impact on policy and investment, because we waste time on money on programs that have no chance of success.
Trying to remain ignorant isn't going to help us here, even if we have good intentions.
And presumably learn from it. While wasting a lot of money and effort (and people) on programs that won't work isn't good, neither is not trying because the effect is presumed, pre hoc, to be small or non-existent.
We live in a world where most people aren't enabled to achieve their potential. Figuring out that extrinsic rewards don't work to motivate behavioral changes or achievement for some people of a certain category, regardless of why, will hopefully result in the testing of other non-extrinsic-reward interventions that may work to motivate.
While it might be easier than for regular people, it's still extremely hard for a politician/academic or political faction/academic faction to admit error. It's almost always possible to come up with a reason for why something didn't work that doesn't require giving up on a centrally important idea.
Normally you look for deficits in people in order to account for them with special help, but this is a science just looking to shed blame. It's like testing for dyslexia to find kids that you shouldn't bother trying to teach to read. Or even worse, retroactively justifying your decision not to teach redheaded kids how to read by doing a survey of redheaded kids who were never taught to read, over a dozen generations, and finding them stupid.
That's the problem. The field is hopelessly tainted, and being an area that would be difficult under any circumstances (due to mass social effects rather than mass genetic effects), meaningful designs would be hard to find even if the researchers were motivated by something other than justifying the past.
In my experience, the people most obsessed with arguing and proving the usefulness of IQ are somewhere between 110-120. The people obsessed with the heritability of IQ and the supposed dominance of nature over nurture are often people who have raised terrible children.
aside: one thing I'm curious about and haven't found is that there are a number of researchers who show differences between American black achievement (slave descendants) and black immigrants from Africa and the Caribbean (who started arriving in 1965.) I haven't seen a lot of race science speculating about that: did slavers (either Western or the Africans who sold them) have some sort of filter that only put the stupid blacks into slavery? Were all the smart ones culled, and/or their intelligence intentionally bred out of them over generations? Did the admixture of the genetics of so many white slavers into their slave stock lower slave intelligence, or raise their propensity to violence? Or does that entire line of inquiry (or intense study of slave breeding in general) hold no interest for people trying to justify 18th century race science?
Governments offering free embryo selection plausibly.
IQ is 50 to 80% inherited [1]. (We can only predict about 10% of it with genetics [2].)
Note that heritability numbers are specific to a particular environment. E.g. if you have a more random environment with some kids exposed to lead poisoning, some to malnourishment and some to parasites you will get lower heritability figures.
Most studies on this are conducted in countries like Sweden and the USA on middle class populations.