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As the Democratic primary campaign heats up, the conversation is taking an unfortunate turn when it comes to discussion of candidates' ages. Late-night hosts such as Jimmy Fallon "joke" that Bernie Sanders, age 77, is sponsored by Metamucil and was present for the signing of the American Constitution. The pundits are hardly better than the comedians when discussing candidates' ages: In columns like these, they compare old age to a "shipwreck" and worry that "old duffers" are a danger to the republic.

As two humanists who study the culture of old age, we view such rhetoric as a distraction from serious issues and feel it reproduces inaccurate stereotypes about aging. One of the most important conversations we will be having in the 21st century concerns old age. The number of Americans over age 65 is going to double in the next 40 years, a demographic fact that opens up major questions about social support, care work and political economy.

An election season with a number of candidates over 65 could provide an opportunity for us to confront our unexamined prejudices against older people. And yet the mainstream media has done little more than circulate and reproduce the ageist stereotypes that physicians and activists have long been laboring to overturn.

The near-unanimous consensus of gerontologists in the past several decades has been that elderly people are more cognitively capable and adaptable than our prejudices indicate. The vast majority of people in their 70s do not show signs of dementia. While it is true that subtle cognitive decline is nearly inevitable for all of us, different sorts of intelligence are affected at different rates. Indeed, the effects of aging are far from homogenous or predictable, which is why we reject Robert Kaiser's recent suggestion that the risk of mental decline is grounds for disqualifying older candidates.

History shows that it is a dangerous game to politicize clinical data about a certain group's "intelligence" or capacity. Even if one did want to play that game, it remains to be argued whether the specific sorts of reasonably expected decline would lead to incompetence in the specific tasks of the modern American presidency - which are, to state the obvious, not the tasks replicated in the lab.

The question of whether elderly people are suited for executive office can be better answered with the tools of history. And history suggests that they are: South African leader Nelson Mandela, Britain's Winston Churchill and Konrad Adenauer, chancellor of West Germany for 14 years after the end of World War II, were all highly effective political leaders well into their 70s. Those worried about aging leaders might have in mind Ronald Reagan and Pope John Paul II, whose leadership capacity was affected by Alzheimer's and Parkinson's disease, respectively. We should remember, though, that neither of those diseases is especially common, and about 90 percent of the population over 65 is not afflicted by either.

The mismatch between popular ideas and scholarly research should not surprise us. History shows, too, that the devaluation of old age has more to do with culture and economics than it does with biology.

As recently as the 18th century, in the wake of the American Revolution, elderly people were valued as sources of wisdom and experience. This was an era before geriatrics and before "retirement": The notion that one exited the labor market at the age of 65 was unknown. Aging was certainly viewed as a form of decline, but it was also viewed as a naturally occurring process, to be welcomed and respected. Physicians who thought about old age, such as Benjamin Rush, wondered about how patients might achieve old age - not how old age and its infirmities might be cured.

It was only with the shift to a more market-driven and capitalist economy in the 19th century that we reached what historian W. Andrew Achenbaum calls a "watershed in which the overall estimation of old people's worth clearly changed." Industrialized, wage-based economies had less room for elderly bodies, while the new cult of vitalism and health led to valorization of the youth as the lifeblood of the nation. In 1905, William Osler, the first physician in chief at Johns Hopkins Hospital, gave voice to popular sentiment when he described "the comparative uselessness of men above the age of forty." Neurologists such as George Miller Beard echoed this idea, arguing for 40 instead of 65 as the endpoint of professional utility.

This denigration of the potential of older people coincided with a demographic explosion in their numbers. Over the course of the 20th century, this led to the novel idea that they should "retire" (from the French retirer, meaning "to withdraw"). To be sure, a leisure-filled retirement has always been out of reach for many. And yet the cultural ideal of old age was no longer linked with spiritual uplift but with shuffleboard and mental decline.

Given this history, it is no surprise that ageism can seem like a more acceptable form of prejudice than others. This is also perhaps because older people are embedded into the establishment as "old white men." However common, this phrase is misleading. For one thing, most older people are neither male nor white. And for another, whiteness and maleness have a long history of privilege in a way that old age, on its own, does not. Furthermore, the coming generation of elderly people will be considerably less privileged than their forebears, given the deterioration of the welfare system, the undervaluation of care work and the shuttering of nursing facilities.

Rather than contemplate the disqualification of candidates because of their advanced age, we would do well to consider how older candidates might bring a heightened awareness to issues of inequality and discrimination, a wealth of policy expertise, and the adroitness and diplomacy that comes with years of experience in the government. Audre Lorde observed that "the generation gap is an important social tool for any repressive society." If we view older candidates with suspicion and contempt merely because of their age, we risk missing out on the potential for intergenerational collaboration - a crucial resource in the graying century to come.

Chappel is the Hunt Family assistant professor of history at Duke University and a senior fellow at Duke's Center for Aging and the Study of Human Development. Edelstein is associate professor of English at University of Massachusetts, Boston and author of "Adulthood and Other Fictions: American Literature and the Unmaking of Age."