Sarah K. Cowan, a sociology and demography  grad student at UC Berkeley, recently asked CNN readers, “What if a President served 42 years?”   That’s how long Moammar Gadhafi has been the leader in Libya, which could be equated to Richard Nixon still serving as President of the United States today rather than leaving office in 1974.

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.

But, in many countries, a large portion of the population has only experienced 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…

According to Cowan, two main factors have led to situations where much of the population knows only one leader.  First, that leader remained in power and disregarded or never established term limits.  Second, the populations in these countries are comparatively young.

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.)

Opinions on the benefits of long-standing rulers vary.  Some scholars argue that they create political and social vacuums and stunt economic growth, while others argue that, under the right conditions, long tenures may lead to economic growth.  Either way, Cowan says:

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.”