To facilitate discussion, in what follows the names 'Jeanne Calment' and 'Yvonne Calment' refer to the women born in 1875 and 1898, respectively, regardless of when these women died; and the name 'Mme Calment' refers to the woman who died in 1997, regardless of when she was born.
Jeanne Calment (born 21 February 1875) was, until recently, widely considered to have died on 4 August 1997 and to be, as such, the oldest verified person in history, reaching the remarkable age of 122 years and 164 days. In 2018, Russian mathematician Nikolay Zak—prompted by Valery Novoselov, an assistant professor of gerontology and geriatrics at RUDN University in Moscow—uploaded a paper to ResearchGate, subsequently published in the journal Rejuvenation Research, challenging this view. Zak argued that the person who died in 1997 was Jeanne Calment's daughter, Yvonne Calment (born 29 January 1898), who upon Jeanne's death in 1934 assumed her official identity for tax evasion purposes.
Versions of this “identity switch hypothesis” had been advanced in the past (including by fellow Metaculites), but it was only with the publication of Zak’s paper and its popularization and further development by life-extension activist Yuri Deigin in a series of blog posts that the thesis attracted widespread attention and discussion. The main facts adduced in support of this hypothesis are, to quote from Gwern's useful summary, "the suspiciousness of the Calment family archives being destroyed by them, some anomalies in Calment’s passport, oddities in family arrangements, apparent inconsistency of Calment’s recollections & timing of events & photos, facial landmarks like ear features not seeming to match up between young/old photos, and an obscure 2007 accusation in a French book that a French bureaucrat and/or the insurance company had uncovered the fraud but the French state quietly suppressed the findings because of Calment’s national fame."
The response of the professional community of demographers has been generally skeptical. Jean-Marie Robine, a respected scholar who co-validated Calment's longevity record, was particularly critical: "You can talk with any scholar, who would say, we would not accept this even from a student. It’s not scientific, there’s no methodology, no hypothesis, no nothing." His colleague and co-author Michel Allard also criticized the study, though he noted that "even if far-fetched, the Russians’ conclusions should be given consideration." After a "rather tense" meeting of the National Institute for Demographic Studies in early 2019, longevity experts from France, Swiss and Belgium concluded that an exhumation may be needed to settle the controversy.
More recently, it has been discovered that blood samples taken from Mme Calment have been preserved by the Fondation Jean Dausset-CEPH in Paris. Furthermore, researcher Phil Gibbs and gerontologist Aubrey De Grey independently noted that, because of inbreeding, Yvonne Calment had only 12 great-great-grandparents, whereas Jeanne Calment had the usual 16. Thus, the true identity of Mme Calment could be straightforwardly established by conducting a single DNA test on a blood sample already in possession of a laboratory.
In light of this, we now ask: Conditional on relevant DNA tests being carried out, will it be shown that Mme Calment was Jeanne Calment?
The question will resolve before the official resolution date (January 1, 2030) if and when the results of a DNA test of Mme Calment, following either an exhumation of her body or an analysis of a preserved blood sample, are officially announced. The resolution will then be determined as follows:
If the DNA of the exhumed body or the blood sample is shown to be that of someone with 12 great-great-grandparents, the question resolves negative; if it is shown the be that of someone with 16 great-great-grandparents, it resolves positive; otherwise, it resolves ambiguous.
If the official body of Yvonne Calment is also exhumed and tested, the question resolves negative if DNA testing shows Mme Calment to be Yvonne Calment, and positive otherwise.
In the unlikely event that both of the criteria above become relevant and yield inconsistent resolutions, the question will resolve according to criterion (2).
In all these cases, the question will retroactively close one week before the test results are officially announced.
If the question doesn't resolve before the official resolution date, it will resolve ambiguous.
In addition to the writings listed above, readers may want to consult the following papers:
Zak & Gibbs, A Bayesian Assessment of the Longevity of Jeanne Calment (in favor of the ID switch hypothesis).
Robine, Allard, Herrmann & Jeune, The Real Facts Supporting Jeanne Calment as the Oldest Ever Human (against the ID switch hypothesis).