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Hereditarianism is the doctrine or school of thought that heredity plays a significant role in determining human nature and character traits, such as intelligence and personality. Hereditarians believe in the power of genetics to explain human character traits and solve human social and political problems. Hereditarians adopt the view that an understanding of human evolution can extend the understanding of human nature.
Social scientist Barry Mehler defines hereditarianism as "the belief that a substantial part of both group and individual differences in human behavioral traits are caused by genetic differences". [1] Hereditarianism is sometimes used as a synonym for biological or genetic determinism, though some scholars distinguish the two terms. When distinguished, biological determinism is used to mean that heredity is the only factor. Supporters of hereditarianism reject this sense of biological determinism for most cases. However, in some cases genetic determinism is true; for example, Matt Ridley describes Huntington's disease as "pure fatalism, undiluted by environmental variability". [2] In other cases, hereditarians would see no role for genes; for example, the condition of "not knowing a word of Chinese" has nothing to do (directly) with genes. [3]
Hereditarians point to the heritability of cognitive ability, and the outsized influence that cognitive ability has on life outcomes, as evidence in favor of the hereditarian viewpoint. [4] According to Plomin and Van Stumm (2018), "Intelligence is highly heritable and predicts important educational, occupational and health outcomes better than any other trait." [5] Estimates for the heritability of intelligence range from 20% in infancy to 80% in adulthood. [6] [7]
Francis Galton is generally considered the father of hereditarianism. [1] In his book Hereditary Genius (1869), Galton pioneered research on the heredity of intelligence. Galton continued research into the heredity of human behavior in his later works, including "The History of Twins" (1875) [8] and Inquiries into Human Faculty and Its Development (1883).
The Bell Curve (1994), by psychologist Richard Herrnstein and political scientist Charles Murray, argued that the heritability of cognitive ability, combined with a modern American society in which cognitive ability is the leading determinant of success, was leading to an increasingly rich and segregated "cognitive elite". [9] [10] Herrnstein and Murray also examined how cognitive ability predicts socially desirable behavior. [9] They also discussed the debate regarding race and intelligence, concluding that the evidence to date didn't justify an estimate on the degree of influence of genetics versus environmental causes for average differences in IQ test performance between racial groups. [11] Today the scientific consensus is that genetics does not explain such differences, and that they are rather environmental in origin. [12] [13] [14] [15] [16] [17]
Cognitive psychologist Steven Pinker, in his book The Blank Slate (2002), argues that biology explains much more about human nature than people generally acknowledge. [18]
Theories opposed to hereditarianism include behaviorism, social determinism and environmental determinism.[ citation needed ] This disagreement and controversy is part of the nature versus nurture debate. But both are based on the assumption that genes and environment have large independent effects.[ citation needed ] The dominant view outside psychology among biologists and geneticists is that both of these are gross oversimplifications and that the behavioral/psychological phenotype for human beings is determined by a function of genes and environment which cannot be decomposed into a sum of functions of the two independently.[ citation needed ] And this especially because human behavior is uniquely plastic compared to that of other animals.[ citation needed ] The commonly cited heritability, h2, is meaningful only in the context of the independent effects model.[ citation needed ] This model may be a good approximation to the real function given that the range of genomes and the range of environments is sufficiently narrow, e.g., white upper middle class Americans living in Chicago.[ citation needed ] Ronald C. Bailey argues that hereditarianism is based on five fallacious assumptions. In a 1997 paper, he also wrote that "...behavior geneticists will continue to be very limited in their ability to partition the effects of genes, the environment, and their covariance and interaction on human behavior and cognitive ability." [19]
In 1949, Nicolas Pastore claimed that hereditarians were more likely to be conservative, [20] that they view social and economic inequality as a natural result of variation in talent and character. Consequently, they explain class and race differences as the result of partly genetic group differences. Pastore contrasted this with the claim that behaviorists were more likely to be liberals or leftists, that they believe economic disadvantage and structural problems in the social order were to blame for group differences. [20]
However, the historical correspondence between hereditarianism and conservatism has broken down at least among proponents of hereditarianism. Philosopher Peter Singer describes his vision of a new liberal political view that embraces hereditarianism in his 1999 book, A Darwinian Left . [21]
Arthur Robert Jensen was an American psychologist and writer. He was a professor of educational psychology at the University of California, Berkeley. Jensen was known for his work in psychometrics and differential psychology, the study of how and why individuals differ behaviorally from one another.
An intelligence quotient (IQ) is a total score derived from a set of standardised tests or subtests designed to assess human intelligence. The abbreviation "IQ" was coined by the psychologist William Stern for the German term Intelligenzquotient, his term for a scoring method for intelligence tests at University of Breslau he advocated in a 1912 book.
Discussions of race and intelligence – specifically, claims of differences in intelligence along racial lines – have appeared in both popular science and academic research since the modern concept of race was first introduced. With the inception of IQ testing in the early 20th century, differences in average test performance between racial groups were observed, though these differences have fluctuated and in many cases steadily decreased over time. Further complicating the issue, modern science has shown race to be a social construct rather than a biological reality, and intelligence has no undisputed definition. The validity of IQ testing as a metric for human intelligence is itself disputed. Today, the scientific consensus is that genetics does not explain differences in IQ test performance between groups, and that observed differences are environmental in origin.
The Bell Curve: Intelligence and Class Structure in American Life is a 1994 book by psychologist Richard J. Herrnstein and political scientist Charles Murray, in which the authors argue that human intelligence is substantially influenced by both inherited and environmental factors and that it is a better predictor of many personal outcomes, including financial income, job performance, birth out of wedlock, and involvement in crime than are an individual's parental socioeconomic status. They also argue that those with high intelligence, the "cognitive elite", are becoming separated from those of average and below-average intelligence, and that this separation is a source of social division within the United States.
The Mismeasure of Man is a 1981 book by paleontologist Stephen Jay Gould. The book is both a history and critique of the statistical methods and cultural motivations underlying biological determinism, the belief that "the social and economic differences between human groups—primarily races, classes, and sexes—arise from inherited, inborn distinctions and that society, in this sense, is an accurate reflection of biology".
Nature versus nurture is a long-standing debate in biology and society about the balance between two competing factors which determine fate: genetics (nature) and environment (nurture). The alliterative expression "nature and nurture" in English has been in use since at least the Elizabethan period and goes back to medieval French.
Biological determinism, also known as genetic determinism, is the belief that human behaviour is directly controlled by an individual's genes or some component of their physiology, generally at the expense of the role of the environment, whether in embryonic development or in learning. Genetic reductionism is a similar concept, but it is distinct from genetic determinism in that the former refers to the level of understanding, while the latter refers to the supposedly causal role of genes. Biological determinism has been associated with movements in science and society including eugenics, scientific racism, and the debates around the heritability of IQ, the basis of sexual orientation, and sociobiology.
Heritability is a statistic used in the fields of breeding and genetics that estimates the degree of variation in a phenotypic trait in a population that is due to genetic variation between individuals in that population. The concept of heritability can be expressed in the form of the following question: "What is the proportion of the variation in a given trait within a population that is not explained by the environment or random chance?"
Twin studies are studies conducted on identical or fraternal twins. They aim to reveal the importance of environmental and genetic influences for traits, phenotypes, and disorders. Twin research is considered a key tool in behavioral genetics and in related fields, from biology to psychology. Twin studies are part of the broader methodology used in behavior genetics, which uses all data that are genetically informative – siblings studies, adoption studies, pedigree, etc. These studies have been used to track traits ranging from personal behavior to the presentation of severe mental illnesses such as schizophrenia.
The g factor is a construct developed in psychometric investigations of cognitive abilities and human intelligence. It is a variable that summarizes positive correlations among different cognitive tasks, reflecting the fact that an individual's performance on one type of cognitive task tends to be comparable to that person's performance on other kinds of cognitive tasks. The g factor typically accounts for 40 to 50 percent of the between-individual performance differences on a given cognitive test, and composite scores based on many tests are frequently regarded as estimates of individuals' standing on the g factor. The terms IQ, general intelligence, general cognitive ability, general mental ability, and simply intelligence are often used interchangeably to refer to this common core shared by cognitive tests. However, the g factor itself is merely a mathematical construct indicating the level of observed correlation between cognitive tasks. The measured value of this construct depends on the cognitive tasks that are used, and little is known about the underlying causes of the observed correlations.
Human behaviour genetics is an interdisciplinary subfield of behaviour genetics that studies the role of genetic and environmental influences on human behaviour. Classically, human behavioural geneticists have studied the inheritance of behavioural traits. The field was originally focused on determining the importance of genetic influences on human behaviour. It has evolved to address more complex questions such as: how important are genetic and/or environmental influences on various human behavioural traits; to what extent do the same genetic and/or environmental influences impact the overlap between human behavioural traits; how do genetic and/or environmental influences on behaviour change across development; and what environmental factors moderate the importance of genetic effects on human behaviour. The field is interdisciplinary, and draws from genetics, psychology, and statistics. Most recently, the field has moved into the area of statistical genetics, with many behavioural geneticists also involved in efforts to identify the specific genes involved in human behaviour, and to understand how the effects associated with these genes changes across time, and in conjunction with the environment.
Research on the heritability of IQ inquires into the degree of variation in IQ within a population that is due to genetic variation between individuals in that population. There has been significant controversy in the academic community about the heritability of IQ since research on the issue began in the late nineteenth century. Intelligence in the normal range is a polygenic trait, meaning that it is influenced by more than one gene, and in the case of intelligence at least 500 genes. Further, explaining the similarity in IQ of closely related persons requires careful study because environmental factors may be correlated with genetic factors.
"Mainstream Science on Intelligence" was a public statement issued by a group of researchers of topics associated with intelligence testing. It was published originally in The Wall Street Journal on December 13, 1994, as a response to criticism of the book The Bell Curve by Richard Herrnstein and Charles Murray, which appeared earlier the same year. The statement defended Herrnstein and Murray's controversial claims about race and intelligence.
The study of height and intelligence examines correlations between height and human intelligence. Some epidemiological research on the subject has shown that there is a small but statistically significant positive correlation between height and intelligence after controlling for socioeconomic class and parental education. The cited study, however, does not draw any conclusions about height and intelligence, but rather suggests "a continuing effect of post-natal growth on childhood cognition beyond the age of 9 years." This correlation arises in both the developed and developing world and persists across age groups. An individual’s taller stature has been attributed to higher economic status, which often translates to a higher quality of nutrition. This correlation, however, can be inverted to characterize one’s socioeconomic status as a consequence of stature, where shorter stature can attract discrimination that affects many factors, among them employment, and treatment by educators. One such theory argues that since height strongly correlates with white and gray matter volume, it may act as a biomarker for cerebral development which itself mediates intelligence. Competing explanations include that certain genetic factors may influence both height and intelligence, or that both height and intelligence may be affected in similar ways by adverse environmental exposures during development. Measurements of the total surface area and mean thickness of the cortical grey matter using a magnetic resonance imaging (MRI) revealed that the height of individuals had a positive correlation with the total cortical surface area. This supports the idea that genes that influence height also influence total surface area of the brain, which in turn influences intelligence, resulting in the correlation. Other explanations further qualify the positive correlation between height and intelligence, suggesting that because the correlation becomes weaker with higher socioeconomic class and education level, environmental factors could partially override any genetic factors affecting both characteristics.
The IQ Controversy, the Media and Public Policy is a book published by Smith College professor emeritus Stanley Rothman and Harvard researcher Mark Snyderman in 1988. Claiming to document liberal bias in media coverage of scientific findings regarding intelligence quotient (IQ), the book builds on a survey of the opinions of hundreds of North American psychologists, sociologists and educationalists conducted by the authors in 1984. The book also includes an analysis of the reporting on intelligence testing by the press and television in the US for the period 1969–1983, as well as an opinion poll of 207 journalists and 86 science editors about IQ testing.
In multivariate quantitative genetics, a genetic correlation is the proportion of variance that two traits share due to genetic causes, the correlation between the genetic influences on a trait and the genetic influences on a different trait estimating the degree of pleiotropy or causal overlap. A genetic correlation of 0 implies that the genetic effects on one trait are independent of the other, while a correlation of 1 implies that all of the genetic influences on the two traits are identical. The bivariate genetic correlation can be generalized to inferring genetic latent variable factors across > 2 traits using factor analysis. Genetic correlation models were introduced into behavioral genetics in the 1970s–1980s.
Behavioural genetics, also referred to as behaviour genetics, is a field of scientific research that uses genetic methods to investigate the nature and origins of individual differences in behaviour. While the name "behavioural genetics" connotes a focus on genetic influences, the field broadly investigates the extent to which genetic and environmental factors influence individual differences, and the development of research designs that can remove the confounding of genes and environment. Behavioural genetics was founded as a scientific discipline by Francis Galton in the late 19th century, only to be discredited through association with eugenics movements before and during World War II. In the latter half of the 20th century, the field saw renewed prominence with research on inheritance of behaviour and mental illness in humans, as well as research on genetically informative model organisms through selective breeding and crosses. In the late 20th and early 21st centuries, technological advances in molecular genetics made it possible to measure and modify the genome directly. This led to major advances in model organism research and in human studies, leading to new scientific discoveries.
The history of the race and intelligence controversy concerns the historical development of a debate about possible explanations of group differences encountered in the study of race and intelligence. Since the beginning of IQ testing around the time of World War I, there have been observed differences between the average scores of different population groups, and there have been debates over whether this is mainly due to environmental and cultural factors, or mainly due to some as yet undiscovered genetic factor, or whether such a dichotomy between environmental and genetic factors is the appropriate framing of the debate. Today, the scientific consensus is that genetics does not explain differences in IQ test performance between racial groups.
Blueprint: How DNA Makes Us Who We Are is a book by behavioral geneticist Robert Plomin, first published in 2018 by the MIT Press and Allen Lane. The book argues that genetic factors, and specifically variations in individuals' DNA, has a large effect on human psychological traits, accounting for approximately half of all variation in such traits. The book also claims that genes play a more important role in people's personalities than does the environment. In Blueprint, Plomin argues that environmental effects on human psychological differences, although they exist, are "...mostly random – unsystematic and unstable – which means that we cannot do much about them."
In behavioral genetics, the Scarr–Rowe effect, also known as the Scarr–Rowe hypothesis, refers to the proposed moderating effect of low socioeconomic status on the heritability of children's IQ. According to this hypothesis, lower socioeconomic status and greater exposure to social disadvantage during childhood leads to a decrease in the heritability of IQ, as compared to children raised in more advantaged environments. It is considered an example of gene–environment interaction. This hypothesized effect was first proposed by Sandra Scarr, who found support for it in a 1971 study of twins in Philadelphia, and these results were replicated by David C. Rowe in 1999. Since then, similar results have been replicated numerous times, though not all replication studies have yielded positive results. A 2015 meta-analysis found that the effect was predominant in the United States while less evident in societies with robust child welfare systems.
There is an emerging consensus about racial and gender equality in genetic determinants of intelligence; most researchers, including ourselves, agree that genes do not explain between-group differences.
[T]he claims that genetics defines racial groups and makes them different, that IQ and cultural differences among racial groups are caused by genes, and that racial inequalities within and between nations are the inevitable outcome of long evolutionary processes are neither new nor supported by science (either old or new).
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