The Heritability of IQ
It is widely accepted that intelligence is a trait that is passed down through the generations and the degree to which the intelligence quotient (IQ) is dependent on your genetic background has been extensively researched. For example, several traits are known to be primarily genetic, such as adult height or eye colour whereas other traits have low heritability, meaning that they are heavily influenced by the environment – such as depression in men. The way this is measured is by seeing how much a certain trait varies in people with very similar or different genetic and environmental backgrounds.
Thus, it is believed that genetics can account for 75% of your adult intelligence, with the environment being responsible for the remaining 25%. However, what is interesting is that research has found only a few specific genes which have a distinct, substantial effect on IQ – which means that intelligence is probably the result of the action of numerous genes, and their interaction with environmental stimuli, rather than the product of a specific “intelligence gene”.
The Social Development of IQ
Despite the big role that genetic plays in determining intelligence, social and environmental factors can have an important influence too. In fact, research shows that aside from genes and formal education, early family environments also play a crucial role. Evidence shows that a baby’s intelligence is not fully developed at birth but gradually evolves and changes, especially throughout the early elementary school years.
Parents actually a greater impact on their child’s IQ than any other person or institution in the child’s life, including schools and this impact is greatest during infancy and childhood, up to the age of eight or nine, after which parental influence diminishes. Things parents can do to improve their child’s IQ include: maintaining your own education, getting good nutrition and prenatal care, spending as much time with the child as possible, interacting and stimulating his mind through reading, shapes, numbers, colours, etc and exposing the child to experience outside the home.
Certain studies have linked specific activities with improved mental function. For example, one piece of research suggests that musical training can lead to the development of higher brain functions and in particular, better mathematical ability. Music is believed to enhance the brain's ability to visualise and transform objects in space and time, as well as the ‘hard wiring' for spatial-temporal reasoning. Another study showed that babies brought up in a stimulating environment (starting from in the womb) were more dynamic, alert and curious, with good hand-eye coordination and high social skills.
Keeping up the Challenge
Many researchers believe that human and animal brains remain “plastic” throughout their lifetimes, with a great capacity to change. This means that our brains remain strongly influenced by environmental conditions. In fact, studies have shown that stimulating environments increase brain thickness, the number of neurons in the brain and the number of connections between these neurons. In addition, putting the test subject back in a boring environment produced a decrease in responses by as much as 60% within a week. All this supports the advice to continually stimulate your brain throughout your life, even after reaching adulthood, and to promote the development of a broad range of interest and skills which are mental, physical, aesthetic, social and emotional.
Intelligence: Heredity-Environment Debate Resolved?
According to neuro and cognitive scientists, different intellectual abilities are based on neural circuits that require environmental stimulation for development -- and are open to change.
However, intelligence researchers argue that there is a general factor of intelligence ("G") that is highly heritable and defines intelligence as an overall innate ability to perform well on different measures of intelligence -- which are not open to change.
This debate is reviewed in an analysis of 124 studies of the underlying basis of intelligence in the January issue of Psychological Review published by the American Psychological Association.
Does one have to be a child Einstein to be an adult Einstein? Yes, if the developing brain has the ability to make the right connections, according to this theory.
"You could present a person with an IQ of 200 with the appropriate phenomena when they are 20 years old, after the critical learning period, and they would not have the capacity to adapt their brains to the new phenomena,"
Intelligence varies with at least 21 factors
Some of the other circumstances and attributes that have been found to vary to a greater or lesser (but always significant) extent in relation with IQ (Bouchard & Segal, 1985; Liungman, 1975) - note that not all of these relationships support an environmental view.
Intelligence varies with:
• Infant malnutrition (-ve)
• Birth weight
• Birth order
• Number of siblings (-ve)
• Number of years in school
• Social group of parental home
• Father's profession
• Father's economic status
• Degree of parental rigidity (-ve)
• Parental ambition
• Mother's education
• Average TV viewing (-ve)
• Average book-reading
• Self-confidence according to attitude scale measurement
• Age (negative relationship, applies only in adulthood)
• Degree of authority in parental home (-ve)
• Criminality (-ve)
• Alcoholism (-ve)
• Mental disease (-ve)
• Emotional adaptation
"No single environmental factor seems to have a large influence on IQ. Variables widely believed to be important are usually weak....Even though many studies fail to find strong environmental effects....most of the factors studied do influence IQ in the direction predicted by the investigator....environmental effects are multifactorial and largely unrelated to each other."
So, it would appear that there are many psychological and biological factors each contributing a small a small fraction to the variance in IQ scores.
So, what can we say about nature vs. nurture as causal determinants of intelligence?:
"In the field of intelligence, there are three facts about the transmission of intelligence that virtually everyone seems to accept:
1. Both heredity and environment contribute to intelligence.
2. Heredity and environment interact in various ways.
3. Extremely poor as well as highly enriched environments can interfere with the realization of a person's intelligence, regardless of the person's heredity. Although most would accept a causal role of genetics, the exact genetic link and how it operates is very far from being understood - another point that most psychologists would agree on. It is certainly not a single gene, but a complex combination of smaller genetic markers.
5. But likewise, it is difficult to pin-down single, identifiable elements of the environment which directly influence IQ scores. Several environmental factors influence intelligence.
So what have we learned about intelligence: that it’s difficult to define but that there is SOMETHING we call intelligence that appears to relate to ability to reason abstractly, to learn and to adapt. That we can measure some part of it, although poorly; that it’s
partially caused by genetics, partially be environment; that the real causes are the complex, not well understood interplay between genetics and environment; that it is somewhat though not greatly modifiable; that sometimes what we learn from tests is used inappropriately but that IQ tests can be useful in helping children attain their potentia