The Dark Triad Abnormal Development or Base Human Nature? I propose the concept, that human beings, as animals have the same instincts as other animals. Even though we are social animals, we still have the basic nature of fight and flight and we teach ourselves to overrule these with the "conscious mind" or frontal lobe. To help reinforce the practice of inhibiting behaviour that "may" be destructive to other human beings, are many laws, and  social and organisational constructs of "morality" (eg religion, schooling). These practices assist in the individuals development of conscience.

This leads me to a group of people who fail to conform to the social norms that are supposed to help to  ensure that human beings have the optimal chance to overcome base desires and instincts. 

The Dark Triad;
Narcissism
Machiavellianism
Psychopathy

The key features being;
lack of empathy
self-centredness
lack of remorse    

From the pure analysis that the percentage of people with these diagnoses are not the norm. It can be argued that these people are defective, as they are not the norm. It has been argued these personality types can be genetic and caused by environment and every permutation between. One could, almost argue that it is the underlying "default" of human nature, when all our conditioning is stripped away.

My question is:
Are people diagnosed with Narcissism, Machiavellianism or Psychopathy  truly different; or are these set of personality traits dormant within all people?
The Dark Triad traits you speak of are subclinical personality traits, therefore they cannot be diagnosed. Everyone carries some of the characteristics of these traits. People high on these traits are also not considered to be defective, even better they may in some environments be considered to be an advantage (e.g., business areas).

You may want to read up on research on the Dark Triad, mainly that by Dr. P. K. Jonason. He is one of the main contributors to the Dark Triad research and uses an evolutionary paradigm to discuss his research, showing how the Dark Triad may be adaptive.