MadSci Network: Neuroscience


Date: Wed May 5 15:27:59 1999
Posted By: Salvatore Cullari, Professor and Chair, Lebanon Valley College
Area of science: Neuroscience
ID: 924928310.Ns

	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 
	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!

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