Is Intelligence Genetic or Not?

There are numerous studies being conducted today to answer a question that most of the normal population has never thought about. The question whether or not intelligence is inherited and if intelligence is influenced genetically? Some agree that intelligence is genetically influenced, while others disagree saying genetics play almost no role in level of intelligence. Those who say there is no genetic connection claim that environment and available resources play the biggest part in a person’s intelligence. More or less it comes down to the infamous debate of nature versus nurture.
The following will discuss some of the experiments that are being conducted to answer such a question and results from prior experiments that have been conducted. Also this report will discuss some of the statistical influence that nurture has on the level of intelligence. The main focus of this article is to give information making people more conscious of the subject.

Past Years

In past years the goal of geneticist was to determine whether or not intelligence was heritable. Most studies in past years where conducted on monozygotic twins (meaning coming from one egg) and dizygotic (coming from separate eggs). The reason these test where conducted on twins is because monozygotic twins DNA are more identical than that of a clones. Therefore there would be little variants in their DNA strands making it easier to identify very minute differences. The test of the past conducted on twins showed that general intelligence was very heritable. In fact the result showed that as much as 40% in children and 80% in adults was inherited according to studies conducted by Danielle Posthuma and Eco. De Geus(151). Other studies done in the past showed that other factors influenced the level of general intelligence things such as protein level and brain size.

Current Studies

However, current studies that are being conducted are not necessarily looking at the heritability of intelligence but, specific gene loci that is affiliated with intelligence. These studies are conducted in two different ways, linkage analysis and candidate gene association. In linkage analysis there are gene markers that are evenly distributed along the entire length of a chromosome in known locations of two genetically similar individuals (Posthuma and Geus 152). Gene markers are simply landmarks along a genome that can be small discrepancies in a base pair or numerous repeats in nucleotides. Each DNA marker is evident to a particular traits, traits ranging from physical attributes to cognitive ability. Gene association is basically genes that are in the general vicinity of a gene marker. Usually genes that are near a gene maker are associated with the function of the gene marker. Also gene loci that are located in the same position on different people of similar genetic background usually perform the same function or code for the same trait. The reason for this assumption is because genes are transcribed in chunks.

Recent Studies and Results

In recent years there have been many studies over this topic that has been published. The first whole genome linkage scan for intelligence was published in 2005 by Danielle Posthuma. Several more have been published since 2006 by several individuals. The first study done by Posthuma was a sample of 159 Dutch sibling pairs of genomes(152). The results from this test concluded that there were two significant linkages to general intelligence, one linkage on the long arm of the chromosome 2, the other linkage on the short arm of chromosome 6 (Posthuma 152). The linkage on chromosome 2 has also been linked to such mental disabilities as autism and dyslexia (Posthuma 152). Two more studies have been conducted to have similar findings. Confirming that chromosome 2 and 6 has particular influences on IQ score. A study conducted later by Luciano showed that word recognition was directly related to chromosome 2 (Posthuma and Geus 152). Other studies have confirmed to direct linkage to chromosome 14 as well. In further studies that where conducted by Hill, Chorney, Lubinshi, Thompson, and Plomin in 2002 found a more specific variant in a person’s intelligence. This was a chemical compound called Aldehyde Dehydrogenase 5 the gene that was found to increase the activity of this chemical was the ALDH5A1 gene found on chromosome 6 (Plomin). Increased levels of this chemical in the brain resulted in higher amounts of brain function and increased levels of IQ. There are various other genes that have been speculated to influence intelligence but have not been proven some of these genes are CTSD, PRNP, DRD2, CBS, BDNF and COMT (Postuma and Geus 153).

The Nurture Side of the Debate

Now for the nurture side of the debate, it is obvious that there are some genetics involved with a person’s intelligence levels. However several people will debate that the influence of these genetic factors fails in comparison to that of the influence of environment. Psychological researchers of the subject claim that variables such as a parent’s education, available resourses and educational reading play the largest role in determining a person’s level of intelligence. Statistics shown in a study conducted by Lewis Terman that one fourth of every gifted child had a parent who graduated from college (30). Studies show that the parents of the gifted children had completed more than twice as much education as the average adult (Terman 30). Proving that a large portion of a person’s intelligence is greatly influenced by the environment in which they are surrounded. Having parents that attended college would increase the likelihood of having educational resources at a childs disposal, therefore increasing the chances of attending schools of higher academic standards.

So Who Plays the Bigger Role Nature or Nurture?

Influencing intelligence is largely a combination of genetic background along with a fertilized environment for intellectual growth. It seems that both factors based on current findings and experiments play an enormous role in determining a person’s intelligence. Genetics obviously makes up the foundation for intelligence. Environment on the other hand plays the big role in whether or not intelligence expands upon that foundation. There is no way to say which has the greater role in intelligence but it is hard to believe that a high or low level of intelligence can be obtained without the influence of both factors. In conclusion the equation is simple you cannot have one without the other.