Is Intelligence Hereditary?

Is intelligence hereditary?

Is intelligence hereditary?

Check out this answer from Consensus:

Intelligence is a highly heritable trait influenced by both genetic and environmental factors. Recent genetic research has provided significant insights into the heritability of intelligence, identifying specific genetic variants that contribute to cognitive abilities. However, environmental influences and ethical considerations must also be taken into account. As research progresses, it is essential to approach the study of intelligence with a balanced perspective, recognizing the complex interplay between nature and nurture.

 

The question of whether intelligence is hereditary has intrigued scientists for decades. Intelligence, defined as the ability to learn, reason, and solve problems, is a complex trait influenced by both genetic and environmental factors. Recent advancements in genetic research have provided significant insights into the heritability of intelligence, shedding light on the genetic architecture that underpins cognitive abilities. This article explores the genetic basis of intelligence, the role of environmental factors, and the implications of these findings.

Genetic Basis of Intelligence

Heritability Estimates

Intelligence is one of the most heritable behavioral traits. Studies have shown that the heritability of intelligence increases from about 20% in infancy to approximately 80% in later adulthood2. This suggests that genetic factors play a more significant role as individuals age. Genome-wide association studies (GWAS) have identified inherited genome sequence differences that account for 20% of the 50% heritability of intelligence1. These findings highlight the substantial genetic contribution to intelligence.

Genetic Correlations

Research has demonstrated that intelligence captures genetic effects on diverse cognitive and learning abilities, which correlate phenotypically about 0.30 on average but correlate genetically about 0.60 or higher2. This indicates that the same genetic factors influence various cognitive abilities, supporting the notion of a general intelligence factor (g).

Assortative Mating

Assortative mating, the tendency for individuals to mate with others who have similar traits, is greater for intelligence than for other behavioral traits such as personality and psychopathology2. This phenomenon pumps additive genetic variance into the population every generation, contributing to the high narrow heritability of intelligence.

Environmental Influences

While genetic factors play a significant role in determining intelligence, environmental influences cannot be overlooked. Shared environments, such as the maternal womb environment and common home environment, account for a portion of the covariance between relatives’ IQs3. Maternal effects, often assumed to be negligible, account for 20% of the covariance between twins and 5% between siblings3. These findings suggest that both genetic and environmental factors contribute to intelligence.

Implications and Controversies

Social Bias and Ethical Considerations

The history of research on the genetics of intelligence is fraught with social bias. During the eugenics era, the hereditary theory of intelligence justified policies that encouraged the proliferation of favored races and stemmed procreation by disfavored ones4. Today, most scientists studying the genetics of intelligence distance themselves from this history by arguing that their research need not investigate intellectual differences between social groups4. However, the ethical implications of this research remain a topic of debate.

Future Directions

The most exciting direction for genetic research on intelligence is to harness the power of the Human Genome Project to identify specific genes responsible for the heritability of intelligence6. Functional genomics, which aims to understand the brain pathways between genes and intelligence, represents a promising avenue for future research6. Additionally, understanding the basis for maternal effects may provide insights into ways to enhance IQ3.

 

Is intelligence hereditary?

Dimitri van der Linden has answered Near Certain

An expert from Erasmus University Rotterdam in Psychology

There is a tremendous amount of empirical research clearly showing that intelligence is hereditary. The estimates range somewhere between .50 to .80 (and are likely closer towards the latter). Obviously, each line of research on this topic (e.g., twin studies, adoption studies, GWAS) has its own specific limitations. Yet, despite such limitations, the different lines of research converge on the conclusion that intelligence is heritable.

The type of evidence comes from many directions. Just to name a few prominent ones:

1) Twin studies that distinguish between genetic and environmental aspects show a substantial heritable component.

2) Adoption studies show that the intelligence of the adopted child more strongly resembles the intelligence of the biological parents than the adoption parents.

3) The heriability coefficient of intelligence actually increases with increasing age. Which would not be expected if it is mainly the environment that would have the strongest influence.

There still may be some debate about the exact estimate of the heritability coefficient (for example, whether it is more closely to 60 or to 80%). But, based on the available evidence that has been collected during the last hundred fifty year or so, I don’t think that there can be much doubt that intelligence is quite strongly heritable.

 

Is intelligence hereditary?

Thomas J Bouchard Jr has answered Near Certain

An expert from University of Minnesota in Psychology, Neuropsychology

The term hereditary in this context is ambiguous. A more precise question with regard to intelligence is; “Is variation in intelligence influenced by genes?” The answer is yes, but the degree of influence (heritability) depends on age.

Genetic influence on intelligence in young children is much less than in adults. In the past genetic influence had been confirmed using twin and adoption studies (kinship studies). Current research using methods that analyze DNA (Genome Wide Association Studies or GWAS) also confirm genetic influence on intelligence. These new studies have not yet demonstrated as high a degree of genetic influence as the kinship studies. This is true for other traits such as height as well. This is work in progress. The heritability of IQ in adulthood estimated by kinship studies is in the range .70 to .80.

Bouchard, T. J., Jr. (2013). The Wilson Effect: The increase in heritability of IQ with age. Twin Research and Human Genetics, 16, 923-930. doi:10.1017/thg.2013.54

 

Is intelligence hereditary?

Nicholas J Grahame has answered Near Certain

An expert from Indiana University ? Purdue University Indianapolis in Psychology, Genetics

Intelligence is heritable, even more so than features like height and weight. Adoption and twin studies offer the best evidence of this. Children adopted at very young ages resemble their adoptive parents in terms of IQ test scores when they are children (i.e., age 5 and younger). As they grow older, though, they increasingly resemble their biological parents. By the time these children are 16 or so, about 70 to 80% of the differences among individuals can be chalked up to their biological parents’ genes, rather than the environment in which they were raised. In other words, if you want to know what a person’s IQ will be, look to the IQ of the biological parents rather than the adoptive parents. These kinds of studies show compellingly how important our genes are in determining our intelligence.

 

Is intelligence hereditary?

Michelle Luciano has answered Near Certain

An expert from Edinburgh University in Psychology

Twin studies and genome wide studies show that intelligence as measured by psychometric tests is around 50% heritable.

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