|MadSci Network: Neuroscience|
Dear Phillip, you have asked a very interesting question that humans have debated for thousands of years. Unfortunately, we still do not have a definitive answer about this, but I will address several issues relevant to your question. First of all, it sounds like you are already assuming that our IQ level is innate. That is, that we are born with a certain level of IQ. This idea is not something that all scientists agree with. For example, there are at least three different possibilities surrounding our IQ level (and perhaps a few others we have not even considered yet). First, you might be right in that certain people are born with a high IQ and others with a low IQ. In other words, that each of us is born with a certain IQ level. The assumption here is that our genetic make-up determines our IQ. Certain genetic combinations may result in high IQs and others in lower ones. There is some evidence to support this. For example, comparable IQ levels seem to run in families. In a similar manner, the more genes you share with someone (for example, siblings share 50% of genes and identical twins share 100%), the greater the correlation (similarity) between IQ scores. However, it may be that our environment plays the crucial role in the development of our IQ. In this case, it may be that environmental conditions such as the type of family we are brought up in, prenatal conditions, environmental stimulation or perhaps even the types of food that we eat which really determines our IQ. Many studies show that children who are raised in an "enriched" environment (more stimulation) develop a higher IQ than children raised in a deprived environment. We also know for example that pregnant mothers who become infected with German measles usually have children who are mentally retarded. Also, a lot of Japanese mothers who were pregnant during the explosion of the atomic bomb during World War II had children with mental retardation. However, the cause of the majority of cases of mental retardation, which is defined as an IQ below 70, is unknown. A third explanation, and probably the most likely one, is that IQ is determined by both hereditary and environmental conditions. This is the one that I think most scientists would favor these days. A common explanation is that our genetic make-up sets the upper (and perhaps lower) limits of our IQ, but that the environment determines whether we actually meet this potential. For example, if you were very poor and did not have access to books, art, literature or a quality education, your IQ would never develop to your full potential. In this case, even if genetic factors were the primary determinants of IQ, our environment might be responsible for perhaps 15 (plus or minus) IQ points or more. Thus, our environment would determine whether our IQ was above or below average. One of the factors that affects our IQ level is what scientists call “regression towards the mean.” For example, lets say that your parents' IQ scores are both 145 (which is higher than 99% of the population). It is likely that your own IQ (or those of your siblings) would be closer to the mean IQ of your ancestors, which is approximately 100. In this case, your IQ level would most likely be less than your parents. The same would be true if your parents IQ was 70. In this case, your IQ would most likely be higher than theirs and closer to 100. Notice that the mean IQ level across generations stays approximately the same, which is about 100. By the way, the same regression towards the mean occurs for physical attributes such as height. One of the conditions that really plays a major role in this argument is how IQ is measured. Unfortunately, our current technology does not allow us to measure attributes such as IQ directly. We can take direct measurements of height, weight and body temperature, but we have to measure IQ indirectly through IQ tests. The problem here is that these tests may be inaccurate or perhaps even biased for certain members of our population. In this case, until we find better and more direct ways to measure IQ, we may never really have a good answer to your question. The Internet has literally hundreds of different sites which discuss various aspects of IQ. Here are just a few to get you started (note that some of these are for older students). Thank-you for a great question! http://www.chre.vt.edu/cdfs/lectures/chapter9/index.htm http://brain.com/bboard/read/iq-archive2/2363 http://brain.com/bboard/read/iq-archive2/1762 http://www.bebbo.demon.co.uk/iqmyth.html
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