The role or contribution of heredity and environment is a classic debates in the field of psychology. Most theorists believe that in the contemporary times, the both the heredity as well as environmental factors play a combined role in the shaping of the personality of the individuals, including the state of their physical and psychological health. This is also called nature vs. nurture debate. Originally many theorists believed that the heredity alone determine the fate of the individuals' intelligence and life success as a result of that intelligence. The book called The Bell Curve by Herrnstein and Murray (1994) described the studies done by the two intelligence researchers and they confidently said that race has a key role to play in the intelligence. They said that African Americans have lower intelligence level than Caucasians, because of the African descent. This proposal caused a lot of unrest in the history of the intelligence theory. Theorists who aimed at exploring the environmental effects on the intelligence, later on came forward with the hypotheses that intelligence in malleable. They described their theses and backed it with studies done on twins to show that inheritance does not affect the intelligence over the course of the life time, after all, that on the contrary, with favorable environmental opportunities the even hereditary disadvantage can be minimized. .
Furthermore, due to this welcome line of research, in the human cognition field, the concept of neural plasticity and the flexibility of the human intelligence came to surface.

Programs like Head Start might make a significant difference as some research shows, primarily because it is the shift in the environmental factors which make it possible to allow for the positive use of mental abilities of children who are other wise unable to grow into creative and intelligent students.

Recent research in Intelligence theory has shown consistently that nurture and nature debate go hand in hand, and that no single factor is responsible for the lack of optimal intelligence in any given individual, but a combination of factors, including predisposition to lower achievement, but which can also be corrected by introduction of positive environmental factors. These risk factors can all have a bearing on the malleability of the intelligence in a child or an adult learner.

IQ tests have been around for a century now ever since Simon Binet's intelligence tests have been used. Now a days, standardized tests are also used to indicate the predictability of the IQ and the achievement of the students who are given the IQ tests. Therefore, it can be safely stated that IQ tests, may or may not be true indicator of the future academic or career success of anybody, given the fact that other factors in life can make a person become less able to

http://www.surgeongeneral.gov/library/mentalhealth/chapter3/sec2.html

http://en.wikipedia.org/wiki/The_Bell_Curve
http://www.macalester.edu/psychology/whathap/ubnrp/intelligence05/Rheredity.html
http://www.apa.org/releases/iqdebate.html