What Genetics Does And Doesn’t Tell Us

I was looking at various articles and blogs on genetics, race, and IQ. I was also looking at the comments. It got me thinking about the quality of the public debate.

Much of the analysis and discussion is high quality. There are many people involved who are intelligent and well-read. But there still is a lot of misunderstanding and confusion about the issues of heritability, genetic inheritance, and shared environment. Without understanding these issues, there is no way to tackle all the related issues of race, IQ, etc.

This is a topic that I’ve posted about before. In that post, I offered many different perspectives from both online sources and books. If you check out some of the info from that post, you’ll realize how many complex factors are involved in a trait getting passed on and how difficult it is to determine causal relationships, specifically determining genetic influence.

This post is a continuation of what I shared there. I feel compelled to return to the topic because of its importance.

I’ll keep this post simpler, though. I’m only going to offer four articles for consideration, all of them from the website Science 2.0. There is no particular reason I’m offering these articles from this website other than that they caught my attention as I was browsing the web. The authors explain the issues well and I want to use this opportunity to promote their explanations.

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What Is Heritability?
By Gerhard Adam

“Heritability” is a term used in many articles and through much of the scientific literature and invariably promotes the idea that it relates specifically to inherited traits. As a result, it is often assumed that the heritability of a particular trait relates to how much influence genetics has on the trait manifesting in an individual.

However, that isn’t what it means.

Heritability attempts to address the relationship between nature (genetics) and nurture (environment), so that as each changes, the variation between individuals within a population can be estimated based on these influences. In this context, “environment” simply represents everything external to the genome that could effect expression.

Therefore the first significant aspect of heritability that must be understood is that it tells us nothing about individuals. It is strictly an estimate of the variations that occur within populations. If heritability is applied to an individual it is a meaningless concept [since an individual cannot be said to vary with anything].

It also doesn’t tell us anything about the specific influence of genes on any particular trait, since that would be the result of inheritance. We also need to understand that a trait is something that is “selectable”. In other words, there exists a possibility that outcomes can vary in the expression of a particular trait. This follows from the Mendelian view of inheritance where genes are represented as two alleles [dominant and recessive], so that particular combinations would produce certain outcomes. Therefore if there is no variation in the alleles, then everyone has the same genes and heritability would be zero. Adaptations like having a heart or a stomach are not selectable (too many genes and interactions) and therefore tell us nothing about heritability. The primary difference is that adaptations represent the cumulative effect of changes over time that have gone to fixation in a population. As a result, there is no “selection” that would determine “heart or no heart”. Therefore we can consider that the heart is an adaptation, while the risk of heart disease is a trait.

[ . . . . ]

One difficulty that arises with heritability is that any considered trait must be demonstrably linked to genetic transmission. This can become problematic when heritability is used to evaluate behavioral traits where the genetic link may be tenuous. In an effort to measure heritability, there is often a reliance on twin studies under the assumption that variances between them must be accountable to environment since they are effectively genetically identical. However, as previously mentioned, this can result in difficult interpretations when the traits in question are purely behavioral. Until such time as behavioral traits can be explicitly linked to genes, any statement regarding heritability must be considered suspect.

Heritability: A Primer
By Josh Witten

RED FLAG: If someone says the heritability of X is Y, then they probably don’t know what they are talking about.

Folks in the know, know that there are two kinds of heritability, broad sense and narrow sense. Those knowledgeable folks in the know are aware that it is extremely important to clearly state which heritability one is using, as the interpretation of each is different.

[ . . . . ]

Broad sense heritability tells us what proportion of the phenotypic variation is due to the genotypes of the individuals of the population. It tells us nothing about how similar the phenotype of a child will be to its parent. For that, we need the narrow sense heritability.

[ . . . . ]

Human behavioral studies, such as on IQ, have it much more difficult. Environmental variance is very difficult to control experimentally. Statistical methods can be used to correct for the effects of known environmental variables, but one cannot be certain that all variables have been accounted for. Without knowledge of the environmental variance, one cannot determine the value of Cov(G,E). Underestimating environmental variance and assuming, without evidence, that Cov(G,E)=0, will lead to an overestimation of Var(G), Var(A), and both broad and narrow sense heritability.

In this context, it becomes impossible to interpret either broad sense or narrow sense heritability rigorously. It is even questionable whether these metrics have any validity at all.

For a more thorough examination of the issue of heritability of IQ along these lines, I recommend dusting off a Science paper from 1974 by Layzer entitled “Heritability analyses of IQ scores: science or numerology?”.

What Our Genes Tell Us About Race
By Michael White

The debate over race and intelligence has a long and tarnished history, although that doesn’t mean it’s not a legitimate scientific question to address. However, the debate has taken place almost entirely outside modern genetics, falling instead within the realm of psychology (such as work done by Arthur Jensen). Some writers would have you believe that science is converging on a consensus that the ‘IQ’ gap between various races is genetic (and that liberal conspirators are trying to cover it up). That claim is false. Researchers have not identified a single genetic variant with an impact on intelligence that falls along population lines. In fact several studies have recently tested variants in genes that appear to be involved in controlling brain size. No correlation with intelligence was found. Yes, genetics does play a significant role in intelligence, and many other traits. But there is simply no genetic evidence (and I mean real genetics, not psychology) for genetic differences in intelligence between human populations.

Why is this so? Other traits, like skin color, obviously fall along population lines. While skin color is obviously not a 100% reliable predictor, skin color is a major indicator of race. Irish, Kenyans, Pakistanis, and Chinese populations all have clearly different skin tones.

It turns out, not surprisingly, that the genetic variation for some (but not all) skin color genes does in fact follow population divisions, in contrast with most other genetic variation. This is most likely because skin color differences end up being relatively simple – a single variant of a gene (causing lighter skin, for example) can easily become common in a population through natural selection. The result is that you have different human populations with dramatic differences in skin color.

Other traits, however, are much more complex than skin color. Physical differences which are determined not by one, but many different genetic variants, are unlikely to split neatly by population. Intelligence is probably one of the most complex traits humans possess. It is almost certainly affected by variants in many different genes, and many of those genes have other important functions in the body. That means this: two different human populations could have easily developed differences in skin color between them, but differences in intelligence would have been extremely hard to develop, by chance or by natural selection.

Racial conflict has long been a part of human societies. Along with that conflict has come frequent speculation (most famously, but not exclusively among whites with European ancestry) that one race is inferior to another. Some have been worried that modern genetics would substantiate that belief, but our best genetic evidence to date shows those worries unfounded. Genetics does play a large role in the diversity we find among human beings. That diversity, in spite of some dramatic but superficial exceptions like skin color, is shared in common among all races.

Why Race Is Pseudo-Science
By Gerhard Adam

However, the premise is quite simple. If you can’t actually define it in scientific terms, then it cannot be science. Therefore any claims that derive from it are not science. Similarly, we cannot claim that “race” is valid by simply engaging in arm-waving arguments based on the fact that there are genetic differences between various population groups. “Race” must be fully quantifiable as specific heritable trait(s) that serves to identify the group in question.

[ . . . . ]

If the concept of race is to be scientific, then it would need to specifically identify the genetic criteria that is to be used for that differentiation. Merely claiming some external trait isn’t going to do it.

Such simplistic thinking is insufficient to raise the idea of “race” beyond anything except another convenient [or inconvenient as the case may be] cultural grouping.

[ . . . . ]

So, if we really want to pursue the topic of “race” or designating subspecies of humans, then lets do so on a scientific basis, and not some arbitrary socio-cultural designation. If “race” is going to be based on genetics, then it should be intuitively obvious that people will have their “racial” classification changed based solely on their personal family history. As a result, the designation of any particular “race” could actually change from generation to generation. Therefore any claim at racial knowledge that is based on arbitrary external traits rather than the specific genetic traits, is, by definition, wrong 7.

Show me the genes.

http://www.ncbi.nlm.nih.gov/pubmed/15508004

http://www.ncbi.nlm.nih.gov/pubmed/15510170

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC1446406/pdf/11076233.pdf