Hi Sunblue,
I don’t know the research that Brooks is referring to. However, a few points to consider:
The narcissistic people I have known have been particularly sensitive to criticism, slights, etc. This would suggest that their sense of self is fragile.
It is likely that a significant portion (50%) of the propensity to develop full blown NPD is genetic. 50% is the magic number in many personality disorders, schizophrenia, and other "mental disorders". Whether or not the person then develops NPD will depend on a number of different factors in their environment (often argued about). A narcissistic parent obviously doesn’t help!
Narcissism exists on a spectrum: from a lack of narcissism (often in depressed people), to healthy narcissism, to pathological narcissism. Self-deception theory (essentially, if you can fool yourself into believing your are better at something than you really are—then you have a better chance of fooling someone else) suggests that narcissism to some extent should be built into the human race. Healthy narcissism certainly helps people get through hard times, perhaps through soothing distortion.
I'm not sure if this helps, but I thought I would throw it in...
Best,
Richard