Gompertz: derived a formula (in 1825) describing the exponential rise in death rates between sexual maturity and old age.  Began the search for a law of mortality to describe common patterns of senescence.  This is a review/overview of his and subsequent work.

Gompertz’s Law of Mortality

• Linked arithmetic increases in age with geometric increases in death rates
• The “power to oppose destruction” diminishes as a constant (equal amount over equal time)
• Sought a biological explanation: discussed a “hypothetical life force” that destroyed life, and tried to factor that into actuarial calculations
• Chance: the primary or essential element in the cause of death…increased by the diminution of the vital life force…explains why constant quantity of the “vital force” could be varying

Makeham’s Theory of Partial Forces of Mortality (directly building on Gompertz)

• Observed accelerated increases in the force of mortality at older relative to younger ages (3)
• Looked at diseases impacting specific organs (i.e. biological explanations of morality)…the diseases studied thrive on the diminution of vital forces
• The “partitioning” was in reference to examining both extrinsic and intrinsic mortality

The Historical Search for a Law of Mortality (*an odd historical overview—worth skipping)

• Extended the law to all species, assuming differences among species were just a matter of scale
• Looked at specific chemical reactions and major elements of the “life table” (like carbon dating)…“time dependent decay” comparable to Gompertz’s idea on the loss of vital forces
• Random dudes found humans lived longer and attributed it to control over the environment
• Others (including Makeham) questioned the law of mortality primarily because of the “inability to partition total mortality into its intrinsic and extrinsic causes of death” (5)

Biodemography

• Trying to discover “dying out patterns”…why does death occur when it does in individuals?

• Gompertz and Makeham set the stage for improved methods…for example, radiation exposure to test “accelerated senescence” (6) --> significant because it was a physiologically based level of analysis…led to the lethality function calculated for species exposed
• “The modern evolutionary theory of senescence is based on the premise that selection is effective in altering gene frequencies until the time before the end of the reproductive period” (9).  The future is in genetics and demography

Non-Gompertizian Mortality at Older Ages

• Discussion of how Gompertz and Makeham’s work did/does not apply to older ages --> recognition of its inadequacy has led some to unwisely discount it completely
• Facts re: “non-Gompertizian mortality in certain regions of the life span (1-3 on pp. 10-11)

Conclusion

• Gompertz equation/distribution one of the major quantitative tools used in analyzing failure times for living and mechanical organisms…his law of mortality and biological roots verified
• See conceptual framework for intrinsic mortality within biodemography:  b12L to t12R