Natural history of Ashkenazi intelligence

This paper elaborates the hypothesis that the unique demography and sociology of Ashkenazim in medieval Europe selected for intelligence. Ashkenazi literacy, economic specialization, and closure to inward gene flow led to a social environment in which there was high fitness payoff to intelligence, specifically verbal and mathematical intelligence but not spatial ability. As with any regime of strong directional selection on a quantitative trait, genetic variants that were otherwise fitness reducing rose in frequency. In particular we propose that the well-known clusters of Ashkenazi genetic diseases, the sphingolipid cluster and the DNA repair cluster in particular, increase intelligence in heterozygotes. Other Ashkenazi disorders are known to increase intelligence. Although these disorders have been attributed to a bottleneck in Ashkenazi history and consequent genetic drift, there is no evidence of any bottleneck. Gene frequencies at a large number of autosomal loci show that if there was a bottleneck then subsequent gene flow from Europeans must have been very large, obliterating the effects of any bottleneck. The clustering of the disorders in only a few pathways and the presence at elevated frequency of more than one deleterious allele at many of them could not have been produced by drift. Instead these are signatures of strong and recent natural selection.     

Procreative beneficence: why we should select the best children

Eugenic selection of embryos is now possible by employing in vitro fertilization (IVF) and preimplantation genetic diagnosis (PGD). While PGD is currently being employed for the purposes of detecting chromosomal abnormalities or inherited genetic abnormalities, it could in principle be used to test any genetic trait such as hair colour or eye colour.
Genetic research is rapidly progressing into the genetic basis of complex traits like intelligence and a gene has been identified for criminal behaviour in one family. Once the decision to have IVF is made, PGD has few 'costs' to couples, and people would be more inclined to use it to select less serious medical traits, such as a lower risk of developing Alzheimer Disease, or even for non-medical traits. PGD has already been used to select embryos of a desired gender in the absence of any history of sex-linked genetic disease.
I will argue that: (1) some non-disease genes affect the likelihood of us leading the best life; (2) we have a reason to use information which is available about such genes in our reproductive decision-making; (3) couples should select embryos or fetuses which are most likely to have the best life, based on available genetic information, including information about non-disease genes. I will also argue that we should allow selection for non-disease genes even if this maintains or increases social inequality. I will focus on genes for intelligence and sex selection.
I will defend a principle which I call Procreative Beneficence: couples (or single reproducers) should select the child, of the possible children they could have, who is expected to have the best life, or at least as good a life as the others, based on the relevant, available information.     

Beneficence, determinism and justice: an engagement with the argument for the genetic selection of intelligence

In 2001, Julian Savulescu wrote an article entitled 'Procreative Beneficence: Why We Should Select the Best Children', in which he argued for the genetic selection of intelligence in children. That article contributes to a debate on whether genetic research on intelligence should be undertaken at all and, if so, should intelligence selection be available to potential parents. As such, the question of intelligence selection relates to wider issues concerning the genetic determinism of behavioural traits, i.e. alcoholism. This article is designed as an engagement in the intelligence selection debate using an analysis of Savulescu's arguments to raise a series of problematic issues in relation to the ethics of parental selection of intelligence. These problematic issues relate to wider assumptions that are made in order to put forward intelligence selection as a viable ethical option. Such assumptions are more generic in character, but still relate to Savulescu's article, concerning issues of genetic determinism, private allocation and inequality, and, finally, individual versus aggregate justice. The conclusion focuses on what the implications are for the question of agency, especially if intelligence selection is allowed.     

Should we undertake genetic research on intelligence?

Although the concept of intelligence is difficult to define, research has provided evidence for a significant genetic component. Attempts are now being made to use molecular genetic approaches to identify genes contributing to intelligence, and to determine the ways in which they interact with environmental variables. This research is then likely to determine the developmental pathways of intelligence, in an effort to understand mental handicap and learning disorders and develop new treatment strategies. This paper reviews research on the genetic basis of intelligence, and discusses the ethical concerns, including the role of genetic information, the value we place on intelligence and the allocation of resources. It will be argued that the objections raised are problematic, and that because of the value of this knowledge and the prospect of improving lives, this research is morally required. We will then provide a brief analysis of the issues raised by enhancement of intelligence using genetic technology, and will argue that there is no intrinsic difference between this and other means of optimising intelligence.     

Who should fund and control the direction of human behavior genetics? Review of Nuffield Council on Bioethics 2002 Report,Genetics and Human Behaviour: the Ethical Context

In this ( Nuffield Council on Bioethics 2002) , the third in its series on ethics and related issues in genetics (see also Nuffield Council on Bioethics 1993 and Nuffield Council on Bioethics 1998) , the Nuffield Council has focused on four 'normal' behaviors; intelligence, personality, antisocial behavior and sexual orientation. This is a narrow range of behaviors and one where their discussion of the potential impact of predictive genetic testing is probably inappropriate. They also take an unduly narrow view of the purposes of behavior genetics in the 21st century. It is not simply to estimate heritability but to understand more about the structure of behavior and the processes which underlie it. Their narrow focus and their negative approach to the history and achievements of genetics is reflected in their less than positive support for future behavior genetic research. Behavior geneticists need to do more to publicize what their field has achieved in order to counter the very extensive antibehavior genetics initiatives which are almost unique in science. At the same time, organizations such as the Nuffield Council need to consider carefully the impact their deliberations may have on research funding.     

Genetic compatibility, mate choice and patterns of parentage: invited review

There is growing interest in the possibility that genetic compatibility may drive mate choice, including gamete choice, particularly from the perspective of understanding why females frequently mate with more than one male. Mate choice for compatibility differs from other forms of choice for genetic benefits (such as 'good genes') because individuals are expected to differ in their mate preferences, changing the evolutionary dynamics of sexual selection. Recent experiments designed to investigate genetic benefits of polyandry suggest that mate choice on the basis of genetic compatibility may be widespread. However, in most systems the mechanisms responsible for variation in compatibility are unknown. We review potential sources of variation in genetic compatibility and whether there is any evidence for mate choice driven by these factors. Selfish genetic elements appear to have the potential to drive mate compatibility mate choice, though as yet there is only one convincing example. There is abundant evidence for assortative mating between populations in hybrid zones, but very few examples where this is clearly a result of selection against mating with genetically less compatible individuals. There are also numerous cases of inbreeding avoidance, but little evidence that mate choice or differential fertilization success driven by genetic compatibility occurs between unrelated individuals. The exceptions to this are a handful of situations where both the alleles causing incompatibility and the alleles involved in mate choice are located in a chromosome region where recombination is suppressed. As yet there are only a few potential sources of genetic compatibility which have clearly been shown to drive mate choice. This may reflect limitations in the potential for the evolution of mate choice for genetic compatibility within populations, although the most promising sources of such incompatibilities have received relatively little research.     

Rare copy number deletions predict individual variation in intelligence

Phenotypic variation in human intellectual functioning shows substantial heritability, as demonstrated by a long history of behavior genetic studies. Many recent molecular genetic studies have attempted to uncover specific genetic variations responsible for this heritability, but identified effects capture little variance and have proven difficult to replicate. The present study, motivated an interest in “mutation load” emerging from evolutionary perspectives, examined the importance of the number of rare (or infrequent) copy number variations (CNVs), and the total number of base pairs included in such deletions, for psychometric intelligence. Genetic data was collected using the Illumina 1MDuoBeadChip Array from a sample of 202 adult individuals with alcohol dependence, and a subset of these (N = 77) had been administered the Wechsler Abbreviated Scale of Intelligence (WASI). After removing CNV outliers, the impact of rare genetic deletions on psychometric intelligence was investigated in 74 individuals. The total length of the rare deletions significantly and negatively predicted intelligence (r = −.30, p = .01). As prior studies have indicated greater heritability in individuals with relatively higher parental socioeconomic status (SES), we also examined the impact of ethnicity (Anglo/White vs. Other), as a proxy measure of SES; these groups did not differ on any genetic variable. This categorical variable significantly moderated the effect of length of deletions on intelligence, with larger effects being noted in the Anglo/White group. Overall, these results suggest that rare deletions (between 5% and 1% population frequency or less) adversely affect intellectual functioning, and that pleotropic effects might partly account for the association of intelligence with health and mental health status. Significant limitations of this research, including issues of generalizability and CNV measurement, are discussed.     

Testing Someone Else’s Intelligence: From Regimentation to Freedom1

This article discusses the trend in the development of testing from maximum regimentation of the test-takers’ activity (where they solve problems clearly formulated by the creator with a single correct answer) to diagnostic problematic situations that are very new and indefinite with an open beginning and an open end. With increasing frequency, the open beginning used in testing presupposes a freedom of independent formulation of one’s own research questions of the reality being studied and a search for answers while interacting with that reality. The emergence of mass testing of exploratory behavior is a reflection of the conviction that one of the key abilities that will be required in the very near future is the ability to cope with uncertainty and novelty, including by actively investigating them.

The discussion deals with the problems of testing intelligence and creativity in conditions of novelty and uncertainty, including the “judging problem.” It is pointed out that any thinking test, especially a test of creative thinking, is also an implicit (albeit perhaps not conscious) claim by its developers that their wisdom is virtually unsurpassed. After all, it is assumed that any person’s intelligence and creativity that unfold in a new situation may be described in the context of the model produced by the creative intellect of the test’s developer and, hence, by a more powerful “superintellect.” The errors that are practically inevitable with such an approach can be corrected in a dialog among various groups of researchers or, to the contrary, may be deepened if criticism is shut off.

The article analyzes a fundamental methodological error of creativity testing—the “standard list of creative answers” drawn up by the test-maker in advance, against which the participants’ solutions are checked. This error is explored in the case of an invention-oriented task in the international scholastic test PISA 2012, based on which the education ratings of countries are constructed.

An optimistic thesis is offered: no matter how successful testing is, humankind will never be fully prepared to determine its creative potential, due to its forward development. Without diagnostic tools, however, it will be far less prepared; they are a new and important part of that potential.     

Individual Differences in Scotopic Visual Acuity and Contrast Sensitivity: Genetic and Non-Genetic Influences

Despite the large amount of variation found in the night (scotopic) vision capabilities of healthy volunteers, little effort has been made to characterize this variation and factors, genetic and non-genetic, that influence it. In the largest population of healthy observers measured for scotopic visual acuity (VA) and contrast sensitivity (CS) to date, we quantified the effect of a range of variables on visual performance. We found that young volunteers with excellent photopic vision exhibit great variation in their scotopic VA and CS, and this variation is reliable from one testing session to the next. We additionally identified that factors such as Circadian preference, iris color, astigmatism, depression, sex and education have no significant impact on scotopic visual function. We confirmed previous work showing that the amount of time spent on the vision test influences performance and that laser eye surgery results in worse scotopic vision. We also showed a significant effect of intelligence and photopic visual performance on scotopic VA and CS, but all of these variables collectively explain <30% of the variation in scotopic vision. The wide variation seen in young healthy volunteers with excellent photopic vision, the high test-retest agreement, and the vast majority of the variation in scotopic vision remaining unexplained by obvious non-genetic factors suggests a strong genetic component. Our preliminary genome-wide association study (GWAS) of 106 participants ruled out any common genetic variants of very large effect and paves the way for future, larger genetic studies of scotopic vision.     

Blood-based protein biomarkers for diagnosis and classification of neurodegenerative diseases: current progress and clinical potential

Biomarker research is a rapidly advancing field in medicine. Recent advances in genomic, genetic, epigenetic, neuroscientific, proteomic, and metabolomic knowledge and technologies have opened the way to thriving research. In the most general sense, a biomarker refers to any useful characteristic that can be measured and used as an indicator of a normal biologic process, a pathogenic process, or a pharmacologic response to a therapeutic agent. Despite the extensive resources concentrated on this area, there are very few biomarkers currently available that qualify and are satisfactorily validated for mental disorders, and there is still a major lack of biomarkers for typifying neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease. This article provides an overview of this field of research and focuses on recent advances in biomarker research in Alzheimer's disease and Parkinson's disease.     

How general is cognitive ability in non-human animals? A meta-analytical and multi-level reanalysis approach

General intelligence has been a topic of high interest for over a century. Traditionally, research on general intelligence was based on principal component analyses and other dimensionality reduction approaches. The advent of high-speed computing has provided alternative statistical tools that have been used to test predictions of human general intelligence. In comparison, research on general intelligence in non-human animals is in its infancy and still relies mostly on factor-analytical procedures. Here, we argue that dimensionality reduction, when incorrectly applied, can lead to spurious results and limit our understanding of ecological and evolutionary causes of variation in animal cognition. Using a meta-analytical approach, we show, based on 555 bivariate correlations, that the average correlation among cognitive abilities is low (r = 0.185; 95% CI: 0.087–0.287), suggesting relatively weak support for general intelligence in animals. We then use a case study with relatedness (genetic) data to demonstrate how analysing traits using mixed models, without dimensionality reduction, provides new insights into the structure of phenotypic variance among cognitive traits, and uncovers genetic associations that would be hidden otherwise. We hope this article will stimulate the use of alternative tools in the study of cognition and its evolution in animals.     

Genetic Pleiotropy Explains Associations between Musical Auditory Discrimination and Intelligence

Musical aptitude is commonly measured using tasks that involve discrimination of different types of musical auditory stimuli. Performance on such different discrimination tasks correlates positively with each other and with intelligence. However, no study to date has explored these associations using a genetically informative sample to estimate underlying genetic and environmental influences. In the present study, a large sample of Swedish twins (N = 10,500) was used to investigate the genetic architecture of the associations between intelligence and performance on three musical auditory discrimination tasks (rhythm, melody and pitch). Phenotypic correlations between the tasks ranged between 0.23 and 0.42 (Pearson r values). Genetic modelling showed that the covariation between the variables could be explained by shared genetic influences. Neither shared, nor non-shared environment had a significant effect on the associations. Good fit was obtained with a two-factor model where one underlying shared genetic factor explained all the covariation between the musical discrimination tasks and IQ, and a second genetic factor explained variance exclusively shared among the discrimination tasks. The results suggest that positive correlations among musical aptitudes result from both genes with broad effects on cognition, and genes with potentially more specific influences on auditory functions.     

Sexual selection and intelligence: Does sexual reproduction drive the evolution of intelligence?

The basal hypothesis discussed here is the idea that brain architecture could be plastic on a very basal, genetic level due to sexual recombination and reassortment of alleles of genes related to brain development, e.g., neuronal cell adhesion molecules (NCAMs) and others.The role of sexual reassortment leads the study of brain development, species behavior and intelligence to a new version of the so-called “Red Queen Hypothesis”: using the mechanism described here, a kind of runaway selection mechanism seems to arise. Even if NCAMs are almost constant within an individual, they seem to act very differently at the population level and so the role of reassorting polymorphic NCAM- (and other) genes gets particularly clear. If several NCAM-NCAM combinations cause extreme behavior and intelligence variability in a population, these combinations also represent a use of sexual selection. This mechanism of NCAM allele assortment seems to be important for the process of speciation by mutual selection of individuals. Therefore NCAM variants and their associated behaviors are thought to be important for the development of intelligence, in that they promote the attraction of individuals with already high intelligence, leading to the speciation of super-intelligent groups.     

The molecular genetics of cognition: dopamine, COMT and BDNF

The important contribution of genetic factors to the development of cognition and intelligence is widely acknowledged, but identification of these genes has proven to be difficult. Given a variety of evidence implicating the prefrontal cortex and its dopaminergic circuits in cognition, most of the research conducted to date has focused on genes regulating dopaminergic function. Here we review the genetic association studies carried out on catechol-O-methyltransferase (COMT) and the dopamine receptor genes, D1, D2 and D4. In addition, the evidence implicating another promising candidate gene, brain-derived neurotrophic factor (BDNF) in neuropsychological function, is assessed. Both the COMT val158met polymorphism and the BDNF val66met variant appear to influence cognitive function, but the specific neurocognitive processes involved continue to be a matter of debate. Part of the difficulty is distinguishing between false positives, pleiotropy and the influence of a general intelligence factor, g. Also at issue is the complexity of the relevant neuromolecular pathways, which make the inference of simple causal relationships difficult. The implications of molecular genetic cognitive research for psychiatry are discussed in light of these data.     

Genetic correlations between brain volumes and the WAIS-III dimensions of verbal comprehension, working memory, perceptual organization, and processing speed.

We recently showed that the correlation of gray and white matter volume with full scale IQ and the Working Memory dimension are completely mediated by common genetic factors (Posthuma et al., 2002). Here we examine whether the other WAIS III dimensions (Verbal Comprehension, Perceptual Organization, Processing Speed) are also related to gray and white matter volume, and whether any of the dimensions are related to cerebellar volume. Two overlapping samples provided 135 subjects from 60 extended twin families for whom both MRI scans and WAIS III data were available. All three brain volumes are related to Working Memory capacity (r = 0.27). This phenotypic correlation is completely due to a common underlying genetic factor. Processing Speed was genetically related to white matter volume (r(g) = 0.39). Perceptual Organization was both genetically (r(g) = 0.39) and environmentally (r(e) = -0.71) related to cerebellar volume. Verbal Comprehension was not related to any of the three brain volumes. It is concluded that brain volumes are genetically related to intelligence which suggests that genes that influence brain volume may also be important for intelligence. It is also noted however, that the direction of causation (i.e., do genes influence brain volume which in turn influences intelligence, or alternatively, do genes influence intelligence which in turn influences brain volume), or the presence or absence of pleiotropy has not been resolved yet.     

The social and economic origins of genetic determinism: a case history of the American Eugenics Movement, 1900–1940 and its lessons for today

Eugenics, the attempt to improve the genetic quality of the human species by ‘better breeding’, developed as a worldwide movement between 1900 and 1940. It was particularly prominent in the United States, Britain and Germany, and in those countries was based on the then-new science of Mendelian genetics. Eugenicists developed research programs to determine the degree to which traits such as Huntington's chorea, blindness, deafness, mental retardation (feeblemindedness), intelligence, alcoholism, szhiophrenia, manic depression, rebelliousness, nomadism, prostitution and feeble-inhibition were genetically determined. Eugenicists were also active in the political arena, lobbying in the United States for immigration restriction and compulsory sterilization laws for those deemed genetically unfit; in Britain they lobbied for incarceration of genetically unfit and in Germany for sterilization and eventually euthanasia. In all these countries one of the major arguments was that of efficiency: that it was inefficient to allow genetic defects to be multiplied and then have to try and deal with the consequences of state care for the offspring. National Socialists called genetically defective individuals ‘useless eaters’ and argued for sterilization or euthanasia on economic grounds. Similar arguments appeared in the United States and Britain as well. At the present time (1997) much research and publicity is being given to claims about a genetic basis for all the same behaviors (alcoholism, manic depression, etc), again in an economic context – care for people with such diseases is costing too much. There is an important lesson to learn from the past: genetic arguments are put forward to mask the true – social and economic – causes of human behavioral defects. This revised version was published online in August 2006 with corrections to the Cover Date.     

Plastic flies

Individuals within species and populations vary. Such variation arises through environmental and genetic factors and ensures that no two individuals are identical. However, it is clear that not all traits show the same degree of intraspecific variation. Some traits, in particular secondary sexual characteristics used by males to compete for and attract females, are extremely variable among individuals in a population. Other traits, for example brain size in mammals, are not. Recent research has begun to explore the possibility that the extent of phenotypic variation (here referred to as “variability”) may be a character itself and subject to natural selection. While these studies support the concept of variability as an evolvable trait, controversy remains over what precisely the trait is. At the heart of this controversy is the fact that there are very few examples of developmental mechanisms that regulate trait variability in response to any source of variation, be it environmental or genetic. Here, we describe a recent study from our laboratory that identifies such a mechanism. We then place the study in the context of current research on the regulation of trait variability, and discuss the implications for our understanding of the developmental regulation and evolution of phenotypic variation.     

GenClust: A genetic algorithm for clustering gene expression data

Background  

Clustering is a key step in the analysis of gene expression data, and in fact, many classical clustering algorithms are used, or more innovative ones have been designed and validated for the task. Despite the widespread use of artificial intelligence techniques in bioinformatics and, more generally, data analysis, there are very few clustering algorithms based on the genetic paradigm, yet that paradigm has great potential in finding good heuristic solutions to a difficult optimization problem such as clustering.     

Genetik der allgemeinen kognitiven Fähigkeit

Intelligence is one of the best studied constructs of empirical behavioral sciences and represents a general cognitive capacity, which includes – among others – the ability for conceptual thinking, solving challenging problems, abstract thinking, and rapid learning. These cognitive functions play an enormous role in the explanation and prediction of individual differences in central areas of societal life, e.?g., schooling and educational success, professional success, socioeconomic status, and health-related behavior. Behavioral genetic studies have consistently shown that genetic influences make a substantial contribution to defining individual differences, that explain more than 60% of variations in intelligence in adults. Over the last few years, in large genome-wide association studies using frequent genetic variants, hundreds of loci associated with intelligence were identified, in addition to more than 1300 associated genes, which were differentially expressed in the brain. Several pathways were overrepresented, mainly those for neurogenesis, the regulation of nervous system development, and the regulation of synapse structure and activity. Most associated loci were located in regulatory regions and, interestingly, half of them in introns. Of the more than 1300 associated genes, only 9.2% overlapped with those associated with monogenic cognitive defects. Overall, the findings confirm a polygenic model of thousands of additive factors, in which individual loci have a very small effect. Collectively, the current results explain up to 10% of the overall variance in cognitive function. These results are an important starting point for future research, not only in genetics but also in the behavioral sciences.     

On the Use of Factor Scores for Prediction

There are two types of indeterminacy problems in factor analysis: the indeterminacy of the parameters, which is also known as the problem of identification, and the indeterminacy of the factor scores. The second problem, which will be treated here, is of great importance to the social sciences, given that the factor analysis model was historically developed with the theory of measuring intelligence, where the main interest was to determine one person's intelligence numerically. As a consequence of the indeterminacy of factor scores we will show, by means of a numerical example, that any criterion, including the dates of easter sunday, can be perfectly predicted by the intelligence factors.