Human intelligence can be illustrated as the ability to acquire and apply knowledge. Scientists have not yet managed to come to a conclusion about the leading determining factor behind intelligence. Until 60s there were sharply two groups; one who believe that intelligence is a genetically hereditary factor and second, who believe that it is more dependent on environmental factors. R S Woodworth, the famous psychiatrist said, both heredity and environment must be concerned in causing individuals to be different in ability and personality, but it is a real question whether to attach more importance. Progress in genetic and cognitive research has been advanced in the mean time. Every research shed new lights on the debate.
Genetics of intelligence is a branch of behavior genetics that has two famous studies on the debate; one is 'Twin studies' and other is 'Adoption studies'. Twin studies compare IQ of twins reared together and apart because twins are sharing same genes and environments. Modern studies show that almost all traits are somehow influenced by genetic differences. 'Adoption studies' is another powerful tool to understand a child's intelligence as it is being reared up in an environment while having genes from different environment. This study was conducted in 1989 among Korean children aged ten years, who were adopted in Belgian families. It showed that they had higher Visio-spatial abilities yet lower verbal abilities than Belgian children. The explanation was given as - it is genetically programmed in Oriental population.
Let's have a quick revision on gene. Each cell in the human body contains about 25,000 to 35,000 genes, which carry information that determines his traits. Each gene does similar kind of jobs of making protein but each one's assignments are different. A latest scientific estimation reveals that each gene in a cell may make as many as 10 different proteins and all these proteins are keeping our body going. The growth, development, and reproduction of organisms rely on cell division. Organisms inherit the characteristics of their parents because the cells of the offspring contain copies of the genes in their parent's cells. Yet rare, spontaneous alterations in the base sequence of a particular gene may arise. That is called mutation. Mutations propagated to the next generation lead to variations within a species population.
A press release published in October 2009 by Neuropsychiatric Genetics Research Group (NRG) at Trinity College Dublin claimed that, a new genetic variant that influences human intelligence has been discovered by their researchers; though they admitted that further studies will be required to determine the true size of NOS1's effect on human cognition. Same year in May, psychiatric researchers at The Zucker Hillside Hospital campus of The Feinstein Institute for Medical Research have declared that they have found a gene name dysbindin-1 that influence intelligence.
Earlier in 1998, psychologists using a new genetic technique have found a gene associated with high IQ. The technique, they say, should help to identify several more of the many genes thought to affect human intelligence and personality. On 2005, three Portuguese anthropologists HR Correia, SC Balserio and ML Areia proposed the hypothesis that genes of human intelligence are related with metabolism of thyroid and steroids hormones, which have a crucial role in brain development and function.
Dr. Robert Plomin, a leading American behavioral geneticist conducted a very interesting study in 1999. He argued that if genes for intelligence exist it should be possible to track some of them down through the powerful new genetic scanning techniques that were already available then. He found that a particular variant of a certain gene was twice as common in his sample of children with ultra-high IQ as in those with average IQ. The gene had a very small effect, accounting for about 2 percent of the variance, or four IQ points. Only half the children with high IQ in Plomin's study had the intelligence-promoting form of the gene he detected.
The mechanisms by which interaction between genes and environment occur throughout life as well as dynamics of brain structure still remain unknown. Human intelligence has evolved steadily over the course of thousands of generations without drastic change in the environment. There are clear genetic links that incline people to have a larger cerebral cortex, allowing them to better deal with the challenges of the external world. Scientific exploration is still going on to uncover the unknown.