The definition of nepotism you're most likely to encounter is a negative one, used in business and politics. It means hiring or appointing relatives without regard for their abilities or qualifications. If you hire your sister-in-law to manage the information technology (IT) department of your business despite her having no experience or training in IT, you might be accused of nepotism. It's distinct from cronyism, in which jobs are doled out as rewards to friends and people who are owed favors, but not necessarily relatives.
Biologists and other scientists who study animal behavior, however, use the word nepotism to describe any behavior that favors family members over unrelated individuals. Animal nepotism is a result of natural selection (which favors any behaviors that increase the likelihood of genetic traits being passed to another generation), suggesting that nepotism has an overall positive effect on survival rates for some species in certain situations.
Some animal nepotism has a negative effect on an individual animal's chance of surviving while increasing the chance of related animals surviving. For example, ground squirrels who give alarm calls at the approach of a predator are more likely to be killed by predators, but nearby relatives are more likely to survive than if there weren't an alarm call. Studies have found that the squirrels give alarm calls more often when more of their relatives are nearby, and don't give alarm calls when only unrelated squirrels are present [source: Sherman].
Or consider hive insect species like bees and ants. Some individuals are unable to reproduce, devoting their entire lives to helping the hive's queen reproduce successfully. The balance between self-sacrifice and advantage for related animals has even been distilled into a formula, where the reduced survival chances for the individual are weighed against the number of relatives who gain advantage and how closely related they are. The process is known as kin selection, and the formula is called Hamilton's Rule. British Scientist J.B.S. Haldane famously joked about the equation, saying that he would lay down his life "for two brothers, or eight cousins" [source: Dugatin].
The origin of the word "nepotism" lies in some of history's most prolific practitioners of it, Catholic popes. The Latin root nepos means "nephew." Since Catholic priests are forbidden from having sex, popes could never acknowledge the illegitimate sons they fathered. Yet popes wanted to promote their sons (and other relatives, including actual nephews) to important positions within the church. The workaround was to call these unacknowledged sons nephews [source: Sherman]. For example, Pope Sixtus IV had a lot of nephews [source: Metropolitan Museum of Art].
But popes aren't the only people to favor their relatives. Nepotism shows up in every era and culture. Let's look at how it has shaped the world.