Friday, February 01, 2019

Genetic IQ differences between races are likely

This is a respose to "Why genetic IQ differences between 'races' are unlikely"  by Kevin Mitchell
"In the article, Reich emphasises the arbitrary nature of traditional racial groupings, but still argues that long periods of ancestry on separate continents have left their genetic marks on modern populations."
Note that he 'asserts' this, not concludes it based on the massive evidence that is literally as plain as the nose on  your face.

"These are most evident for physical traits like skin and hair colour, where genetic causation is entirely uncontroversial. However, Reich asserts that all genetic traits, including those that affect behaviour and cognition, are expected to differ between populations or races."
Again he characterises Reich's views as assertions.  This is not an argument.

"But it also suggests that since genetic variation will contribute to higher or lower IQ in any given population, the genetic differences between one group and another will also underpin mean differences in IQ.
In fact, the genetics and evolutionary history of intelligence suggest just the opposite."
Note that we're two paragraphs in and he hasn't even started to support this claim.

"Most of our traits, such as height, for example, are set by natural selection at an optimal level "
Actually height is only 80% heritable so it's not exactly 'set' by natural selection, the range within which environment can influence is set by natural selection.  That he made this basic a mistake this early is not encouraging.

"– it’s good for humans to be about so tall, on average. Some genetic variants tend to make people a bit shorter than average and some tend to make people a bit taller. The balance between these variants has been maintained by natural selection to keep average height 'just right'."
Actually it doesn't, it makes height tend towards the optimal from where it was, which is set by what the optimal was in previous generations.  So again, basic mistakes in evolutionary biology.

"Intelligence is not like that. Unlike height, where being ever taller had no benefit, strong evolutionary forces drove intelligence in one direction only in our ancient ancestors."
No that's not true at all for reasons he will actually mention later.  Even if it were true that doesn't mean that all population evolved intelligence at the same speed.

"This increasing selective advantage of ever greater intelligence led to a snowball effect, which was probably only stopped by the limitations of the size of the birth canal and the metabolic demands of a large brain."
Yes, that's right, genes for greater intelligence have COSTS, which means that his claim that there is only evolutionary pressure to increase intelligence is wrong.

"Evolution thus endowed us with a genetic program that holds the instructions of how to build our complex brains, with our resultant cognitive prowess. But any genetic program will be affected by chance mutations and this one is no different. What sets it apart from traits like height is that most genetic random mutations that affect on intelligence will do so negatively."
Here he's using the term "negatively" to mean "have less of this trait".  This is not very helpful since if you take negatively to mean "badly for the organism" the meaning is completely different and his conclusion applies to ALL traits.

"Instead, genetic differences in intelligence may largely reflect the burden of mutations that drag it down."
Or they may reflect mutations that increase intelligence but for some reason have not been fixed.  He actually mentions the reason why some intelligence-boosting genes might not be fixed*.  More on that later. 

"Because most random mutations that affect intelligence will reduce it, evolution will tend to select against them. Inevitably, new mutations will always arise in the population, but ones with a large effect on intelligence – that cause frank intellectual disability, for example – will be swiftly removed by natural selection. Mutations with moderate effects may persist for a few generations, and ones with small effects may last even longer. But because many thousands of genes are involved in brain development, natural selection can’t keep them all free of mutations all the time. It’s like trying to play multiple games of Whack-a-mole at once, with only one hammer.
The result is that any population at any time will carry a varied bunch of mutations that affect intelligence. These will differ between populations, clans, families, and individuals. This constant churn of genetic variation works against any long-term rise or fall in intelligence."
Only if we assume that all intelligence-boosting genes in humans are already fixed.  He really hasn't offered any evidence of this except the supposedly one-way pressure on intelligence.

"Another crucial point is that genetics tends to affect intelligence in a much more indirect way than it does skin colour, height, and other physical traits. Like that Formula One car’s performance, intelligence is an emergent property of the whole system. There is no dedicated genetic module 'for intelligence' that can be acted on independently by natural selection – not without affecting many other traits at the same time, often negatively."
Did you catch that?  The reason why intelligence boosting genes might not have been fixed in the human population yet?  There are human genes that boost intelligence but are disadvantageous in other ways.  These genes are not necessarily advantageous in any given environment.  The advantages of greater intelligence might not be worth the disadvantages of whatever costs the genes inflict.  Also this might change depending on the environment, which would explain genetic differences in intelligence that Mitchell denies can happen. 

"We need to get away from thinking about intelligence as if it were a trait like milk yield in a herd of cattle, controlled by a small, persistent and dedicated bunch of genetic variants that can be selectively bred into animals from one generation to the next."
While it's harder to selectively breed with large numbers of relevant genes it is not impossible.  Another mistake.

"It is quite the opposite – thousands of variants affect intelligence, they are constantly changing, and they affect other traits. It is not impossible for natural selection to produce populations with differences in intelligence, but these factors make it highly unlikely."
Actually it doesn't, if anything it makes it more likely.  For populations to have exactly the same average intelligence is unlikely because the total effect in the change of all genes that affect intelligence would have to be the same, despite there being dozens of such genes that affect other (dis)advantageous traits.

"To end up with systematic genetic differences in intelligence between large, ancient populations, the selective forces driving those differences would need to have been enormous."
No over the thousands of generations that they would have to be less than 0.015 IQ points per generation difference between the selection pressures of various races.

"What’s more, those forces would have to have acted across entire continents, with wildly different environments,"
Actually no, it would have had to have acted in part of an entire continent and the population in that part would have had to have bred with the rest of the continent.

"and have been persistent over tens of thousands of years of tremendous cultural change."
There hasn't been tens of thousands of years of tremendous cultural change, there have been a few thousand such years since we invented farming and herding.  Before that everyone's culture was hunter/gatherer groups.

"Such a scenario is not just speculative – I would argue it is inherently and deeply implausible."
More implausible than the effects of thousands of genes that affect a trait having exactly the same effect in different environments?  Given that hundreds of those genes have other effects that are differentially selected in the various environments this is not just implausible, it's science fiction.

"The bottom line is this. While genetic variation may help to explain why one person is more intelligent than another, there are unlikely to be stable and systematic genetic differences that make one population more intelligent than the next."
Far from supporting this claim Mitchell has actually provided all the evidence to refute it.

"So if we are concerned about people’s intelligence, we would do better to focus on the environmental and cultural factors that we know are involved and which can be changed."
That would depend on what context we're considering the intelligence in.  If you are considering whether the over- or under-representation of a population might be due to discrimination or other factors you HAVE to consider genetics.

"There is no shortage of them: maternal and infant healthcare, early life nutrition, exposure to neurodevelopmental toxins such as lead, and access to and quality of education all make a real difference."
Actually I don't think there's any evidence that education makes a real difference in IQ.

"IQ scores are a measure of a person’s intellectual ability, not the limit of their intellectual potential."
Which has nothing to do with the point.

"Focusing on things we can change should ensure that everyone can reach their potential."
But acknowledging things you can't change is essential if you're going to understand the subject.  But that wasn't what this article was about was it?

* Fixed means that all instances of a species have that genetic mutation.