Biodemography of human longevity

Biodemography is a multidisciplinary approach, integrating biological knowledge (studies on human biology and animal models) with demographic research on human longevity and survival. Biodemographic studies are important for understanding the driving forces of the current longevity revolution (dramatic increase in human life expectancy), forecasting the future of human longevity, and identification of new strategies for further increase in healthy and productive life span.

Biodemographic studies found a remarkable similarity in survival dynamics between humans and laboratory animals. Specifically, three general biodemographic laws of survival are found:

Gompertz-Makeham law of mortality Compensation law of mortality Late-life mortality deceleration.

The Gompertz-Makeham law states that death rate is a sum of age-independent component (Makeham term) and age-dependent component (Gompertz function), which increases exponentially with age.

The Compensation law of mortality (late-life mortality convergence) states that the relative differences in death rates between different populations of the same biological species are decreasing with age, because the higher initial death rates are compensated by lower pace of their increase with age.

The Late-life mortality deceleration law states that death rates stop to increase exponentially at advanced ages and level-off to the late-life mortality plateau. An immediate consequence from this observation is that there is no fixed upper limit to human longevity - there is no special fixed number, which separates possible and impossible values of lifespan. This challenges the common belief in existence of a fixed maximal human life span.

Biodemographic studies found that even genetically identical laboratory animals kept in constant environment have very different lengths of life, suggesting a crucial role of chance and early-life developmental noise in longevity determination. This leads to new approaches in understanding causes of exceptional human longevity.

As for the future of human longevity, biodemographic studies found that evolution of human lifespan had two very distinct stages – the initial stage of mortality decline at younger ages is now replaced by a new trend of preferential improvement of the oldest-old survival. This phenomenon invalidates methods of longevity forecasting based on extrapolation of long-term historical trends.

A general explanation of these biodemograhic laws of aging and longevity has been suggested based on system reliability theory.

Longevity claims

Longevity claims assert extreme human longevity. Those asserting lifespans of 110 years or more are referred to as supercentenarian. 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 such institutions as the Gerontology Research Group (GRG) and/or the Guinness Book of World Records.

Prior to the nineteenth 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. That is, there is no fixed upper limit to human longevity, or fixed maximal human lifespan. This law was first quantified in 1939, when researchers found that the one-year probability of death at advanced age asymptotically approaches a limit of 44% for women and 54% for men.

In 1955, Guinness World Records began maintaining a list of the verified oldest people. It developed[citation needed] into a list of all supercentenarians whose lifespan had been verified by at least three documents, in a standardized process, according the 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 case vary widely in their plausibility.

Only approximately 90 people in modern history have been documented as reaching age 114.

Only 26 of these reached age 115. The oldest person verified by modern standards, and the only person with undisputed evidence to have lived to be over 120, was Jeanne Calment (21 February 1875 – 4 August 1997), a French woman who lived until age 122 years, 164 days. As of 28 June the oldest verified living person is American woman Besse Cooper (born 26 August 1896, age 114 years, 306 days).

In the first two cases of people Guinness acknowledged as having reached age 113, both men's purported ages have now been discredited. In the first three cases of people Guinness acknowledged as having reached age 114, all three purported ages are now in dispute. Of the 10 people regarded by Guinness or the Gerontology Research Group as having reached age 116, three are the subject of substantial doubts. The United States Social Security Administration has public death records of over 100 people said to have died in their 160s to 190s.

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.

Actuary Walter G. Bowerman stated that ill-founded longevity assertions originate mainly in remote, underdeveloped regions, among illiterate peoples, evidenced by nothing more than family testimony.

In the transitional period of record-keeping, records tend to exist for the wealthy and upper-middle classes, but are often spotty and nonexistent for the poor. In the United States, birth registration did not begin in Mississippi until 1912 and was not universal until 1933. Hence, in many longevity cases, no actual birth record exists. This type of case is classified by gerontologists as "partially validated."Proximate records