Are the most intelligent people by genetic inheritance?
Everyone has wondered on occasion 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 the genetics of behavior has managed to respond in detail to this historical doubt.
Research in the field of differential psychology reveals that both the genes and the environment have a very significant weight in the determination of the IQ, the classical measure of intelligence. However, the relevance of the inheritance seems to be slightly higher than that of the environment.
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How is intelligence defined?
The construct "intelligence" is difficult to delimit, given that multiple meanings have been attributed to it both in the lay language and in the scientific community. It is a complex capacity that includes the ability to learn new information, to apply different types of reasoning and to solve problems, among many others.
A special definition is that which has been made from the operational approach. This perspective proposes that intelligence must be defined as "What is measured by the IQ tests" , instruments that have been moderately useful to predict aspects such as work performance and socioeconomic status.
However, intelligence is a very broad attribute and it does not only exist in human beings. It has been defined by many authors as the ability to behave adaptively in complex situations in order to reach a goal; In this type of definitions, the conception of intelligence as a global and stable factor stands out.
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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 estimated that the coefficient of heritability of the IQ oscillates between 0.40 and 0.70. This means that approximately half of the variability is explained by hereditary factors .
From reviews in studies of this type, Antonio Andrés Pueyo concludes that approximately 50% of the variance in intelligence is explained by causes of genetic origin, while the other 50% is due to different environmental factors and random errors of measurement .
In general, older studies have found a greater weight of genetic inheritance in intelligence than recent research. It also seems that the heritability coefficient is higher in cases where the CI is very high (more than 125) or very low (less than 75).
Regarding the different factors that make up intelligence, some studies have found that verbal skills are inherited to a greater extent than manipulative ones. The weight of genetics in verbal IQ increases with age ; the same happens with other components of intelligence, although not in such a remarkable way.
On the other hand, the fluid intelligence described by Raymond B. Cattell, a construct similar to the global factor ("g") originally used by pioneer Charles Spearman, is more influenced by genetic inheritance than crystallized intelligence. While the former is associated with reasoning and the resolution of new problems, the latter refers to accumulated knowledge
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Influence of structure and brain processes
Different authors have pointed out the relevance of the physiological processes of the central nervous system in intelligence. In this sense, structures and functions such as the frontal lobes, the density of the gray matter (composed of neuronal bodies, unmyelinated dendrites and glia) in the brain or the metabolic rate of glucose.
Thus, Vernon wrote that the differences found in the CI tests reflect a greater speed and efficiency in the transmission of nerve impulses, whereas according to Eysenck the most important thing is the number of errors in these connections: if there are fewer failures in transmission, the brain will consume less glucose , reducing the energy effort.
Other studies have linked intelligence measures with blood flow and neurochemical activity in the frontal lobes, as well as the density of gray matter. All these morphological and functional characteristics are inherited to a significant degree, since they depend on the expression of certain genes.
Environmental factors that affect the CI
Intelligence depends largely on the environment. In this sense, a large number of factors are relevant, among which access to quality nutrition, education and health that allow the greatest possible development of the biological potential of each person's brain.
In many cases it is extremely difficult to determine what proportion of the behavioral variability can be attributed to the inheritance and which to the environment, particularly when we talk about the influences relative to the immediate family environment. There is also a reciprocal interaction between genetics and the environment that occurs constantly.
According to Andrés Pueyo, environmental factors account for almost half of the variance in intelligence, a weight very similar to that of genes. Within 50% of variability that is not justified by inheritance attributes 30% to the common or inter-family variance and 10% to the non-shared environment . The error variance ponders another 10% for this author.
Thus, non-shared environmental influences, which differ between persons raised in the same family, seem to be more relevant in the determination of intelligence than the shared environment, although the weight of this is sufficiently high to be taken into consideration.