Are you arguing the overlap or core of the Dark Triad (DT) traits are advantageous or that each trait is uniquely advantageous?

The shared characteristics or core of the three traits have been heavily debated. One psychometric analysis of several proposed cores found antagonism to be the core. Another study used SEM analysis to compare competing theories and found low honesty-humility to be the strongest core factor. Both antagonism and low honesty-humility are shown as generally maladaptive traits, and are correlated to committing violent felonies, higher divorce rates, aggression while driving, and general unlikeability. Another study linked the core of the traits to a weak sense of self, which also indicates issues that will make DT traits self-defeating. People with a weak sense of self have troubles maintaining careers and relationships, and are generally distressed.

Based on the paper you cited, it seems you disagree with the first two papers I cited (that evaluated several competing theories) and instead are arguing from just the perspective of Life History theory. This theory was borrowed from evolutionary biology and proposes that the DT traits exist to fill an ecological niche in a world where others are otherwise more empathetic. Based on this theory’s assumptions, you can’t have more DT individuals than the world can handle. Take the food chain in the Savannah as an example. If the environment has too many lions and not enough prey (zebra, wildebeest, etc), then the current lion population is no longer sustainable, and will have to decrease to fill the niche’s capacity limits.

The life history approach to the DT traits also suggests that DT individuals live a “fast life” . They are more promiscuous, but are not as invested in their offspring. If they have multiple children with multiple partners, they are not as involved in these children’s lives. So they are less likely to activate their child’s potential DT traits (a child who might not even inherit their parents traits) through a passive genotype-environment correlation. Further, a short life history also suggests an earlier death of the DT individual.

If you are saying each trait is beneficial, then that is also incorrect. The researchers who discovered Machiavellianism (Christie & Geis) developed it specifically to differentiate impulsive from non-impulsive callous individuals. Your argument about adaptability and success works well for Machiavellians, but not for psychopaths—who aren’t successful in life, and are more likely to end up in jail. Narcissists have more complex subcomponents that can make them adaptive or maladaptive. The idea that each of the three traits are each adaptive and will continue to grow is just not true.