The Origins of Intelligence

The intelligence quotient (IQ) is the best predictor of success in academia and at work. It also serves as a reliable indicator of longevity [1], making the origin of intelligence and the possibility of enhancing it a most interesting research topic.

The theory of multiple intelligences proposed by Howard Wagner in 1983 outlines nine types [2]. Some of them, such as bodily-kinesthetic intelligence (“body smart”) would be hard to assess using a written test. Yet, it has been shown that people who performed well on any single test section, such as linguistic intelligence, also score high on other areas [2].

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Big Brains Mean More Intellect
Intelligence positively correlates with the size of the whole brain [1]. However, brain size is limited by skull size and the skull has to pass the birth canal. Complications are hence more likely during the birth of naturally intelligent babies, possibly lowering their survival chances. Moreover, the individual volumes of brain areas are highly heritable [1,3], supporting the theory that nature is more influential on intelligence than nurture. Thus, not surprisingly, in diseases that cause dementia, brain cells are lost and the brain effectively shrinks.

Genes for Smartness and Intellectual Disability
Intelligence is a polygenetic trait. This year, the University of Edinburgh announced the discovery of the first intelligence gene. A highly active NPTN gene allows adolescents to score higher on intelligence tests [4]. The gene codes for a neuronal synapse protein that plays a role in brain development and neuronal signaling. Surprisingly, the NPTN gene explains only about 0.5% of the variability in intelligence. Conversely, candidate gene studies have revealed over 282 genes associated with intellectual deficits (formerly known as mental retardation).

“The measure of intelligence is the ability to change.” – Albert Einstein

Results pooled from a number of studies conducted during the last century on human intelligence research indicate that genetic factors are responsible for up to 50% of differences in intelligence between individuals [1,5].

Race over Education or Education over Race?
The philosophy of race superiority suggests that some ‘types’ of humans are superior from birth because of their lineage. Fortunately, this has largely been unpopular since the abolishment of slavery in America (1865) and the defeat of Nazi Germany (1945). Following each of these events, the Caucasian and Afro-American races began to mingle. With the establishment of racially integrated schools, it became apparent that Afro-Americans showed a lower cognitive ability compared to their white peers [5]. This result was partly attributed to their lower socioeconomic status [5], but may have fueled racism in Europe.

Intelligence is an indicator for success

A post-World War II study in Germany looked at the “occupation babies” of Afro-American and Caucasian American soldiers with German mothers. The IQ of the mixed-race children was 96.5 compared to 97 in Caucasian children [6]. This suggested that inheritance of culture, education, and equal opportunity (rather than race) influence IQ.

Dirty Minds at Age 5 Associated with Lower IQ
A study published this year showed that the exposure of pregnant women to air pollution released by the burning of fossil fuels can cause birth defects and lower the IQ of their offspring by about 3.8 points at age 5 [7]. This result persisted even after the scientists accounted for the level of parental education and several other factors that might influence child IQ. Similar studies have shown that pollution is a cause of birth defects, childhood behavioral disorders, and rare cancers [7].

The Recipe for Raising a Genius Is Continuous Practice
In 1993, K. Anders Ericsson presented evidence showing that violinists who practiced more than 10,000 hours before their 20^th birthday were likely to become professionals [6,8]. This was applied to the mastery of other skills and eventually became known as the 10,000 hours rule. Talent plays a lesser role.
A standard IQ test provides no or unreliable results for half of the intelligence types known so far. Intrapersonal intelligence, for example, contributes to good teamwork, stress management, and leadership. However, there is no comprehensive and standardised measure for it [9].
It requires four hours of practice (with coaching and reinforcement), for six days a week, for fifty weeks a year, over ten years will help you master anything! It's no wonder, really. But honestly, how many of us would volunteer to undergo such rigorous training?

[1] Gardner, The Nine Types of Intelligence, http://bit.ly/19kchVz
[2] Deary et al, Eur J Hum Genet, 2006
[3] Science Daily, 2007, http://bit.ly/1s8kvcf
[4] Desrivières et al, Mol Psychiatry, 2014
[5] Dickens, Future Child, 2005
[6] Blech, Spiegel Online, 2010, bit.ly/1pVTiEV
[7] Perera et al, J Public Health Policy, 2014
[8] Ericsson et al, Psychol Rev, 1993
[9] Arora et al, Med Educ, 2010

by Rick Cornell Hellmann, PhD student AG Schwab
This article originally appeared in CNS Volume 7, Issue 3, Nature vs Nurture