Source: American Scientist:
Genes we inherit and environmental factors both influence human behaviors. Scientists have recently discovered other underlying processes at work.
So-called jumping genes, segments of DNA that can copy and paste themselves into new places in the genome, can alter the activity of full-length genes. Occasionally they will turn on neighboring genes in these locations. That activity occurs more in the brain than other areas, resulting in different traits and behaviors, even in closely related individuals.
These mobile genetic elements may also turn out to play a role in people’s disposition to psychiatric disorders.
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Editors Note:
Another interesting link in this regard:
http://www.scientificamerican.com/article.cfm?id=ductile-helix-jumping