Are The Most Intelligent People So By Genetic Inheritance?
Everyone has wondered at some point If the most intelligent people are so by genetic inheritance or because of the environmental influences they receive, such as the quality of nutrition or the education provided by parents. In recent years, behavioral genetics has managed to respond in detail to this historical doubt.
Research in the field of differential psychology reveals that both genes and the environment have a very significant weight in determining IQ, the classic measure of intelligence. However, the relevance of heredity seems to be slightly higher than that of the environment.
The construct “intelligence” is difficult to delimit, since multiple meanings have been attributed to it both in lay 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 solve problems, among many others.
A special definition is the one that has been made from the operational approach. This perspective proposes that intelligence should be defined as “that which is measured by IQ tests” instruments that have been shown to be moderately useful for predicting aspects such as work performance and socioeconomic status.
However, intelligence is a very broad attribute that 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 achieve a goal; In this type of definitions, the conception of intelligence as a global and stable factor stands out.
From the field of behavioral genetics, which analyzes individual differences in behavioral aspects (such as intelligence) using genetic methods, it is estimated that the heritability coefficient of the IQ ranges between 0.40 and 0.70. This means that approximately half of the variability is explained by hereditary factors
Based on reviews of 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 measurement errors..
In general, older studies have found a greater weight of genetic inheritance on intelligence than recent research. Furthermore, it seems that the heritability coefficient is higher in cases where the IQ 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 skills. The weight of genetics on verbal IQ increases with age ; The same happens with other components of intelligence, although not in such a notable way.
On the other hand, 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 first is associated with reasoning and solving new problems, the second refers to accumulated knowledge.
Influence of brain structure and 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 gray matter (composed of neuronal bodies, unmyelinated dendrites and glia) in the brain or the glucose metabolic rate.
Thus, Vernon wrote that the differences found in IQ tests reflect a greater speed and efficiency in the transmission of nervous impulses, while 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 energy effort.
Other studies have linked measures of intelligence 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, since they depend on the expression of certain genes.
Environmental factors that affect IQ
Intelligence depends largely on the environment. In this sense, a large number of factors are relevant, among which stand out access to quality nutrition, education and healthcare 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 behavioral variability can be attributed to heredity and what to environment, particularly when we talk about influences related 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 explain almost half of the variance in intelligence, a weight very similar to that of genes. Within 50% of variability that is not justified by heredity attributes 30% to common or interfamily variance and 10% to the non-shared environment The error variance weights another 10% for this author.
Thus, non-shared environmental influences, which differ between people raised in the same family, seem to be more relevant in determining intelligence than the shared environment, although its weight is high enough to be taken into consideration.
