er studies assumed that human intelligence is a simple quantitative matter such as the height of a person and that genes and environmental effects are added up independently. Today, it is more understood that genes and the environment interact and create varied and complex traits. Genetic structures are complex and human development is dependent on both the genetic background of the person and the interaction of these genes with the environment.
Alwin and Wray (2005) reported on the life span development of the human being and used prior research results to support their conclusions that many environmental factors affect this development. These authors stated that the life-span developmental (LSD) is a perspective that links social factors and physical health. This view incorporates social status factors such as gender and age differences, race and ethnic experiences, and childhood experiences, to explain variances in human development
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