Editor's note: Sarah K. Cowan is a doctoral candidate in sociology and demography at the University of California, Berkeley.
Berkeley, California (CNN) -- Moammar Gadhafi has been the leader of Libya for 42 years. In America, a tenure of that length would be equivalent to Richard Nixon still being president today rather than having left office in 1974.
If America had Libya's kind of government, we would not have won "one for the Gipper," read George H.W. Bush's lips, known who "that woman" was or declared "mission accomplished."
In a healthy democracy, citizens see multiple leaders of government in their lifetime. Doing so allows them to compare leaders, form political preferences and to participate meaningfully in the political process by voting in truly competitive elections.
In many countries, however, a huge portion of the populace has experienced only one leader. Seventy-nine percent of Libyans have lived their entire lives under Gadhafi's rule. Before the revolution in Egypt, 60 percent of Egyptians had lived their lives under President Hosni Mubarak exclusively. Sixty-one percent of Zimbabweans have only known Robert Mugabe's rule.
By contrast, the longest American presidency was Franklin D. Roosevelt's; he was elected four times, to serve for a total of 16 years, of which he served 12 before his death. While there was clear support for such a long tenure from many, there were doubts about it as well. And after Roosevelt's death, passage of the 22nd Amendment established a limit of two four-year terms for a president.
Two factors lead to a situation in which so much of a nation's population knows life under only one leader. First, the leader in these countries has remained in power for decades, either ignoring or eliminating (or never having established) term limits.
The second factor in the proportion of people living under one ruler relates to population dynamics -- these countries have young populations. The median age -- the age where half the population is younger and half is older, in Angola is 18; in contrast, the median age in the United States is 37.
Twenty percent of people in Mozambique have lived their entire lives under Armando Guebuza, and they are all under age 7. The population is so young because women in Mozambique have a lot of children -- more than five on average -- and people die young -- at age 48 on average. (The age of the population can have a powerful effect on these calculations: If Libya had the same age profile as the much older population of the U.S., 57% of the population would have known Gadhafi as the only leader during their lifetime, compared with the 79% who actually did.)
Some of the harm that long-serving dictators can do to their countries is evident in Libya. As Dirk Vandewalle said in a CNN opinion piece in February, "Beyond Gadhafi and a close circle of confidants, there is only an enormous political and social vacuum. There are neither organized groups within Libyan society nor any younger leadership that can assume political duties."
For certain countries, there could be benefits to having leaders of such a long tenure. A number of scholars argue, for instance, that under the right conditions, this can be beneficial for economic growth. But many critics argue that the result of long-serving dictators in the Middle East has been stunted growth for their countries' economies.
Leaving aside whether lengthy tenures are beneficial for economies, they violate democratic principles. It is a characteristic that distinguishes democracies from authoritarian regimes; in a democracy, the leader changes in a reasonable time frame. Term limits, confidence votes for parliamentary systems of government and regular and fair elections are all means by which to prevent "presidents for life."
The opinions expressed in this commentary are solely those of Sarah K. Cowan.