When batteries of tests are administered to samples from non-Western countries, a-factor typically emerges that accounts for approximately half the variance [ 63 ].-factors have even been extracted from test batteries administered to primates and other nonhuman animals [ 64 66 ].

When several different batteries of tests are administered to a sample of individuals and separate-factors are extracted from those batteries, they correlate with one another at around= 0.95 [ 50 51 ].

IQ has a number of important psychometric properties, in virtue of which it has been described as ‘psychology’s greatest single achievement’ [ 23 ], and as one of the ‘of the most reliable and valid instruments in all of psychological science’ [ 48 ]. (In addition to the properties listed, IQ research has higher statistical power than much of the rest of social and medical science [ 49 ]):

Nevertheless, contrary to argument 2.1, intelligence ispseudoscientific. Hence, claims about group differences in cognitive ability made on the basis of differential IQ-test performance are not pseudoscientific either. Intelligence is typically operationalised as the standardised score derived from a battery of mental tests. This operationalisation is based on-factor theory, which posits that a general factor of intelligence influences individuals’ performance across diverse mental tests [ 44 -factor theory is powerful because it accounts for the central fact about intelligence testing, namely that scores on all tests of mental ability (reaction time, vocabulary, mental rotation, etc.) are positively correlated with one another, meaning that individuals who score above average on one test (e.g., reaction time) also tend to score above average on other sub-tests (e.g., vocabulary). It can be contrasted with Gardner’s [ 46 ] theory of multiple intelligences, which denies that a single-factor influences performance across diverse tests. However, Gardner’s theory is no longer given much credence within the psychometrics community. As Deary [ 47 ] notes:

Among psychologists working in this field there is no longer any substantial debate about the structure of human mental ability differences […] A general factor emerges that accounts for about half of the individual differences among the scores for a group of people, and there are group factors that are narrower abilities, and then very specific factors below that.

The first three arguments (2.1, 2.2 and 2.3) all take the same form. Each one is roughly equivalent to the following: ‘Some aspect of the hereditarian hypothesis is pseudoscientific. Pseudoscientific claims about low-scoring groups are tantamount to racial slurs. Therefore, the hereditarian hypothesis is racist.’ When evaluating these three arguments, one might be inclined to object that even a pseudoscientific claim cannot be racist. Rather than being racist, such a claim would simply be wrong (either contradictory, unfalsifiable or patently erroneous). However, it is easy to see how a sufficiently hyperbolic pseudoscientific claim could be construed as a racial slur. For example, consider the following pseudoscientific claim: ‘Blacks score 10 standard deviations below whites on every test of cognitive ability, meaning that there is virtually no overlap between the two distributions.’ It could be argued that, since this claim is so manifestly absurd, the only reasonable way of interpreting it is as a racial slur.

2.2. The Hereditarian Hypothesis is Racist Because There Is no Such Thing as Race

partly biological construct. Before proceeding, it is worth explaining why race is indeed a partly social construct [ Just as IQ is not pseudoscientific, neither is the concept of race as a partly social,biological construct. Before proceeding, it is worth explaining why race is indeed a partly social construct [ 67 ]. One important reason is that systems of racial classification have varied over time and from one society to another [ 68 69 ]. For example, the United States has historically adhered to the so-called ‘one-drop rule’, according to which an individual who has any amount of African ancestry is considered black (say, even someone who had only 1 African great-grandparent out of 8). By contrast, societies such as South Africa and Brazil have long distinguished between ‘black’, ‘white’ and one or more intermediary categories, comprising individuals of mixed ancestry (e.g., ‘coloured’, ‘mullato’). In addition, some early anthropologists used ‘race’ to refer to major continental groups (e.g., ‘Caucasoid’, ‘mongoloid’), whereas others used it refer to finer-grained regional groups (e.g. ‘Nordic’, ‘Celtic’).

Another important reason why race should be seen as a partly social construct is that, in contemporary societies where people are largely free to choose their own racial identity, two individuals with the same mixed ancestry may nonetheless have different racial identities. For example, consider two individuals, each with 1 African great-grandparent and 7 European great-grandparents. One might choose to identify as ‘black’, while the other might choose to identify as ‘mixed race’. And each of them would be perfectly entitled to do so. Some scholars have even gone as far as to argue that it is legitimate for individuals with totally European ancestry to identify as ‘black’, in the same way that it is legitimate for individuals who were born as members of one sex to identify as members of the other sex [ 70 ]. However, this point of view remains a matter of considerable controversy [ 71 ].

partly biological construct too [73,74,75,76,77,78,79,80, essentialist concept of race, which posits that human beings can be divided into a small number of races in such a way that all members of each race share certain traits with one other that they do not share with any members of other races (see [79,83, Of course, just because the meaning of ‘race’ has varied over time and across societies, this does not mean that it is a wholly social construct. Indeed, there is a strong case to be made for treating race as aconstruct too [ 72 81 ]. It is important to note that treating race as a partly biological construct does not imply endorsement of theconcept of race, which posits that human beings can be divided into a small number of races in such a way thatmembers of each race share certain traits with one other that they do not share withmembers of other races (see [ 75 ]). This concept implies that each race has its own ‘essence’, something which is obviously false, and perhaps not even verifiable. As Sesardic [ 75 ] notes, Theodor Dobzhansky pointed out more than 40 years ago that if human populations really were entirely non-overlapping, then ‘we would not have races, we would have distinct species.’ (In other words, the essentialist concept of race is really a straw man.) In fact, the essentialist concept of race is demonstrably false, given that different populations show a relatively large degree of overlap on most traits, the majority of human genetic variation is distributed along a gradient and many humans are of mixed ancestry [ 82 ]. Today, scientists often eschew the term ‘race’ due to its essentialist connotations, instead employing terms such as ‘ancestral population’ or ‘biogeographic ancestry group’ [ 78 84 ]. Note that in any case, nothing about the veracity of research into group differences hinges on whether ‘race’ is valid scientific label. If one objects to claims about ‘race differences’, then one could just as well talk about ‘differences between biogeographic ancestry groups’.

within continental populations is evident from findings such as the one made by Novembre et al. [ Patterns of human genetic variation are influenced by mating patterns, and the latter are in turn influenced by geographic and cultural factors (e.g., mountain ranges, language, religious practices). Consequently, it is not surprising that human genetic variation, while correlated with geographic location, is not perfectly clinal. In contrast to the long-debunked essentialism of the past, a more realistic concept of biological race is one that postulates partially discontinuous genetic variation both within and between ancestral populations. (The existence of population structurecontinental populations is evident from findings such as the one made by Novembre et al. [ 85 ].) This more realistic concept recognises that the discontinuities between ancestral populations correspond to natural geographic barriers, such as oceans (e.g., the Atlantic), deserts (e.g., the Sahara) and mountain ranges (e.g., the Himalayas), which impeded gene flow for substantial periods of time during human evolutionary history [ 86 ]. As Xing et al. [ 87 ] note:

The more realistic concept of race also recognises that, insofar as human population structure can be observed at multiple levels (continental, subcontinental, national, subnational, etc.), there is nothing ‘special’ or ‘natural’ about the continental and subcontinental levels—those which correspond to the concept of race as it has been traditionally understood [ 88 ]. In some scientific contexts, variation between races will matter most, while in other scientific contexts, variation at some other level will matter most. The evidence for this concept of biological race is strong:

Evidence from comparing genetic clusters to racial identities: By genotyping a diverse sample of individuals at a sufficiently large number of genetic loci, and then subjecting the data to cluster analysis, it is possible to classify individuals by race with >95% accuracy [90,91, By genotyping a diverse sample of individuals at a sufficiently large number of genetic loci, and then subjecting the data to cluster analysis, it is possible to classify individuals by race with >95% accuracy [ 89 92 ]. As Edwards [ 93 ] pointed out, due to the correlation structure among loci, correctly classifying individuals by race is possible even though 85–90% of genetic variation is within races.

Evidence from comparisons within and between clusters: When genetic clusters correspond to five major ancestral populations (Africans, Eurasians, East Asians, Amerindians and Australians), subpopulations separated by a given geographic distance are found to be more genetically similar if they are from the same cluster than if they are from different clusters [ When genetic clusters correspond to five major ancestral populations (Africans, Eurasians, East Asians, Amerindians and Australians), subpopulations separated by a given geographic distance are found to be more genetically similar if they are from the same cluster than if they are from different clusters [ 94 ].

Evidence from comparisons across species: The amount of genetic variation between ancestral human populations is comparable to the amount of genetic variation between subspecies in some nonhuman animals for which there are recognised subspecies [ The amount of genetic variation between ancestral human populations is comparable to the amount of genetic variation between subspecies in some nonhuman animals for which there are recognised subspecies [ 74 78 ]. And in fact, overall human mitochondrial variation is about average within the animal kingdom [ 90 ].

Evidence from anatomy and physiology: Ancestral human populations show differences in numerous anatomical and physiological traits [81,95,97,98, Ancestral human populations show differences in numerous anatomical and physiological traits [ 79 96 ]. Moreover, because the differences in such traits are correlated, it is often possible to classify skeletal remains by race with >90% accuracy, so long as a sufficiently large number of traits are measured [ 73 99 ].

Treating race (or ‘biogeographic ancestry group’) as a partly biological construct boils down to the claim that human genetic variation is not perfectly clinal, i.e., that it is at least somewhat discontinuous. However, even if human genetic variation were found to be perfectly clinal, this would not render the hereditarian hypothesis pseudoscientific. On average, there would still be genetic variation between nations and self-identified races, and that variation could in principle covary with their average cognitive abilities. It does not matter for the hereditarian hypothesis whether the genetic variation between groups corresponds to partially discontinuous clusters or arbitrary sections of a continuum.