An extended excerpt:
Egoism, Machiavellianism, narcissism, psychopathy, sadism, spitefulness, and others are among the traits that stand for the malevolent dark sides of human personality. As results from a recently published German-Danish research project show, these traits share a common 'dark core'. So, if you have one of these tendencies, you are also likely to have one or more of the others.
Both world history and everyday life are full of examples of people acting ruthlessly, maliciously, or selfishly. In psychology as well as in everyday language, we have diverse names for the various dark tendencies human may have, most prominently psychopathy (lack of empathy), narcissism (excessive self-absorption), and Machiavellianism (the belief that the ends justify the means), the so-called 'dark triad', along with many others such as egoism, sadism, or spitefulness.
Although at first glance there appear to be noteworthy differences between these traits -- and it may seem more 'acceptable' to be an egoist than a psychopath -- new research shows that all dark aspects of human personality are very closely linked and are based on the same tendency. That is, most dark traits can be understood as flavoured manifestations of a single common underlying disposition: The dark core of personality. In practice, this implies that if you have a tendency to show one of these dark personality traits, you are also more likely to have a strong tendency to display one or more of the others.
As the new research reveals, the common denominator of all dark traits, the D-factor, can be defined as the general tendency to maximize one's individual utility -- disregarding, accepting, or malevolently provoking disutility for others -- , accompanied by beliefs that serve as justifications.
In other words, all dark traits can be traced back to the general tendency of placing one's own goals and interests over those of others even to the extent of taking pleasure in hurting other's -- along with a host of beliefs that serve as justifications and thus prevent feelings of guilt, shame, or the like. The research shows that dark traits in general can be understood as instances of this common core -- although they may differ in which aspects are predominant (e.g., the justifications-aspect is very strong in narcissism whereas the aspect of malevolently provoking disutility is the main feature of sadism) .
The researchers' mapping of the common D-factor, which has just been published in the academic journal Psychological Review, can be compared to how Charles Spearman showed about 100 years ago that people who score highly in one type of intelligence test typically also score highly in other types of intelligence tests, because there is something like a general factor of intelligence.
"In the same way, the dark aspects of human personality also have a common denominator, which means that -- similar to intelligence -- one can say that they are all an expression of the same dispositional tendency," Ingo Zettler explains.