I think we are, maybe in a different way than mvdwood is suggesting. The way I see it is that, the same way one doesn't become asperger or autist, you don't become narcissist, your brain is wired that way, early on during its development, so it's in your DNA and what affects it.

Medical research on narcissism is still very young, but so far we have indication for genetic inheritance and therefore potential genetic markers have been found, we observed defining prefrontal cortex signatures, and reproducible and predictable phenotypes (e.g. atypical responses to an environmental stimulus). Similar trends are also observed in altruism, which is seen as the opposite narcissism.