The debate about nature and nurture excite my curiosity. Is our behavior more influenced by our genes than by the environment in which we grow up? Or is it the opposite? In both cases it is depressing to know that our free will does not really exist! To illustrate this debate, we can focus on only one domain of study: intelligence; and try to answer the two previous questions in the domain of intelligence. What would be your answer?
If you answer yes at the first question, you think that intelligence is mostly influenced by our genes. And you can make a good case for this assumption. You can use the IQ test studies made by Thomas Bouchard from the University of Minnesota and computed by Ridley in his book Genome: The autobiography of a species in 23 chapters. We know from these studies that twins reared together or apart have almost the same scores, whereas adopted children living together have totally different scores. Some studies also show that our spatial and reasoning abilities are mostly due to our genes. So if we take logic to extremes we could say that we cannot do anything to improve our school scores. Bad luck if the nature has not been nice with our brain capacities.
But if you answer yes to the second question, you also have good arguments to support your idea. And you can show us the work of Bouchard and Segal (Handbook of Intelligence: Theories, Measurements, and Applications, 1985) and Liungman (What is IQ? Intelligence, Heredity and Environment, 1975). They both found that intelligence varies with at least 21 factors. Among these 21 factors, there are the social group of the parental home, the average of books read, the degree of parental rigidity, or the number of siblings. So it is not all over at the birth. Everybody can improve his brain capacities; intelligence seems to have a large reaction range. But which are your chances to get high scores at the IQ test if you live in a poor family, socially disadvantaged, with no books at home and parents who are lax with you? They are low. Therefore kids living in socially disadvantaged families have fewer chances to get good results at school than other kids from families with a higher social status.
So the tabula rasa theorem of John Locke is finally maybe not better for the human being than the behavior geneticists' point of view.
That video that I found on Youtube shifts the nature/nurture debate in the domain of criminal behavior: http://www.youtube.com/watch?v=FiUfQ9TXwBw
Bouchard, T. J., & Segal, N. L. (1985). Environment and IQ. In B.B. Wolman (Ed.). Handbook of Intelligence: Theories, Measurements, and Applications (pp. 391-464). New York: John Wiley.
Liungman, C.G. (1975). What is IQ? Intelligence, Heredity and Environment. London: Gordon Cremonesi.
Ridley, M. (1999). Genome: The autobiography of a species in 23 chapters. London: Fourth Estate Ltd.