Everyone wondered at some point if the smartest people are by genetic inheritance or because of the environmental influences they receive, such as the quality of nutrition or education provided by parents. In recent years, behavioral genetics have managed to answer this historical doubt in detail.
Research in the field of differential psychology reveals that genes and the environment have a very important weight in determining IQ, the classic measure of intelligence. However, the relevance of heritage seems to be slightly higher than that of the environment.
How is intelligence defined?
The concept of “intelligence” is difficult to define, as it has been attributed multiple meanings in both layman language and in the scientific community. It is a complex ability that encompasses the ability to learn new information, apply different types of reasoning, and problem solve, among others.
A particular definition is that which was made from the operational approach. This perspective proposes that intelligence be defined as “What is measured by IQ tests”, Tools that have been shown to be moderately useful in predicting aspects such as job performance and socioeconomic status.
However, intelligence is a very broad attribute and it does not exist only in humans. It has been defined by many authors as the ability to behave adaptively in complex situations in order to achieve a goal; in this type of definition, the conception of intelligence as a global and stable factor emerges.
Relationship between genetics and intelligence
From the field of behavioral genetics, which analyzes individual differences in behavioral aspects (such as intelligence) from genetic methods, it is calculated that the heritability coefficient of IQ ranges from 0.40 to 0.70. That means about half of the variability is explained by hereditary factors.
Based on the analyzes of these studies, Antonio Andrés Pueyo concludes that about 50% of the variance in intelligence is explained by causes of genetic origin, while the remaining 50% is due to different environmental factors and random measurement errors.
In general, older studies have found a greater weight of genetic inheritance in intelligence than recent research. In addition, it seems that the coefficient of heritability is higher in cases where the CI is very high (more than 125) or very low (less than 75).
When it comes to the different factors that make up intelligence, some studies have shown that verbal skills are inherited to a greater extent than manipulative skills. The weight of genetics in verbal CI increases with age; the same is true of the other components of intelligence, but not so remarkably well.
On the other hand, the fluid intelligence described by Raymond B. Cattell, a construct similar to the global factor (“g”) originally used by the pioneer Charles Spearman, is more influenced by genetic inheritance than intelligence. crystalline. While the former is associated with reasoning and solving new problems, the latter refers to accumulated knowledge.
Influence of the structure and processes of the brain
Different authors have emphasized the relevance of the physiological processes of the central nervous system for intelligence. In this sense, structures and functions such as frontal lobes, gray matter density (Composed of neuronal bodies, myelinated dendrites and glia) in the brain or the metabolic rate of glucose.
Thus, Vernon wrote that the differences found in the IC tests reflect greater speed and efficiency in the transmission of nerve impulses, while according to Eysenck the most important is the number of errors in these connections: if less transmission errors occur in the brain, it will consume less glucose, Reduce energy effort.
Other studies have linked intelligence measures to blood flow and neurochemical activity in the frontal lobes, as well as gray matter density. All of these morphological and functional characteristics are inherited to a significant degree, as they depend on the expression of certain genes.
Environmental factors affecting IC
Intelligence largely depends on the environment. In this sense, a large number of factors are relevant, among which stand out access to quality nutrition, education and health that allow the greatest possible development of the biological potential of each individual’s brain.
In many cases, it is extremely difficult to determine how much of behavioral variability can be attributed to heredity and how much to the environment, especially when we are talking about influences related to the immediate family environment. There is also a reciprocal interaction between genetics and the environment which is constantly occurring.
According to Andrés Pueyo, environmental factors account for almost half of the variance of intelligence, a weight very similar to that of genes. Less than 50% of the variability not justified by inheritance attributes 30% to the common or inter-family variance and 10% to the non-shared environment. The error variance still weighs 10% for this author.
Thus, unrequited environmental influences, which differ between people raised in the same family, appear to be more relevant in determining intelligence than the shared environment, although the weight of the latter is high enough to be considered. .