Longevity claims are unsubstantiated cases of asserted human longevity. Those asserting lifespans of 110 years or more are referred to as supercentenarians. Many have either no official verification or are backed only by partial evidence. Cases where longevity has been fully verified, according to modern standards of longevity research, are reflected in an established list of supercentenarians based on the work of organizations such as the Gerontology Research Group (GRG) or the Guinness World Records. This list includes claims between 115 years and 130 years.
Prior to the 19th century, there was insufficient evidence either to demonstrate or to refute centenarian longevity. Even today, no fixed theoretical limit to human longevity is apparent. Studies in the biodemography of human longevity indicate a late-life mortality deceleration law: that death rates level off at advanced ages to a late-life mortality plateau. This implies that there is no fixed upper limit to human longevity, or fixed maximum human lifespan. Researchers in Denmark have found a way to determine when a person was born using radiocarbon dating done on the lens of the eye.
In 1955, Guinness World Records began maintaining a list of the verified oldest people. It developed into a list of all supercentenarians whose lifespan had been verified by at least three documents, in a standardized process, according to the norms of modern longevity research. Many unverified cases ("claims" or "traditions") have been controverted by reliable sources. Taking reliable demographic data into account, these unverified cases vary widely in their plausibility.
In numerous editions from the 1960s through the 1980s, Guinness stated that
No single subject is more obscured by vanity, deceit, falsehood, and deliberate fraud than the extremes of human longevity.
Despite demographic evidence of the known extremes of modern longevity, stories in otherwise reliable sources still surface regularly, stating that these extremes have been exceeded. Responsible, modern, scientific validation of human longevity requires investigation of records following an individual from birth to the present (or to death); purported longevity far outside the demonstrated records regularly fail such scrutiny.