The topic can be compared to that of psychological SPITE - where the spiteful person commits acts not really helpful to themselves, and not really destructive to their targets. Here, it is the wider society, the mega-group, that comes into consideration - as it also does in the topic of altruism. But these topics are in other posts.
A selfish gene makes mice into migrants
Usually the cooperation of genes helps an organism to grow and flourish. But some genes are pursuing a different agenda: Their aim is to propagate themselves by eliminating other genes.
House mice carrying a specific selfish supergene move from one population to another much more frequently than their peers. This finding of a University of Zurich study shows for the first time that a gene of this type can influence animal migratory behavior. It could help in dealing with invasive plagues transmitted by mice.
The scientists believe that the supergene manipulates the mice's behavior in this way to enable it to propagate further and further.
Unravelling the genetics of fungal fratricide
Selfish genes are genes that are passed on to the next generation but confer no advantage on the individual as a whole, and may sometimes be harmful. Researchers have, for the first time, sequenced (or charted) two selfish genes in the fungus Neurospora intermedia that cause fungal spores to kill their siblings. Unexpectedly, the genes were not related to each other, perhaps indicating that selfish genes are more common than previously thought.
A 'selfish gene' that poisons its own host
Selfish” Gene Enhances Own Transmission at Expense of Organism's Fertility
How a virus destabilizes the genome
Losing control of gene activity in Alzheimer's disease
Antibodies linked to heart attacks
Cancer stem cells use normal genes in abnormal ways
Co-evolution between a 'parasite gene' and its host
Population mixing promotes arms race host–parasite coevolution
NOTE: You see, selfishness may sometimes seem a short-term gain but, weighed against the always-pressing balance of nature, the best that selfishness can do is to help support symbiotic co-evolution. In an organised human society, selfishness, perhaps contradicting most of our apprehensions, tends not to win out in the long-term. (This is where a game-theory model comes in handy). [In a dysfunctionalising society, or in declining empire, selfishness makes gains - as when a holy hosts of psychopaths gets elected into the top rungs of leadership, whereby they actually sell-out to enemies of the sytem, for selfish gain].
Selfish people have fewer children and earn less money
What happens to those who behave unselfishly and make sacrifices for the sake of others? According to an interdisciplinary study, unselfish people tend both to have more children and to receive higher salaries, in comparison to more selfish people.
Watching a Friend Get Eaten Could Help Animals Learn to Stay Alive
Opinion: The selfish gene is a great meme. Too bad it's so wrong | Aeon Essays