LIFE AND DEATH

View of Life and Death - Aging, Death, and Human Longevity

View of Life and Death - Aging, Death, and Human Longevity

Introduction

Longevity is the period of time, between birth and death of an organism. This definition is misleadingly straightforward, because the point when life begins and ends is a matter of some arbitrariness. Although most definitions of life would begin with birth, arguments have made that life begins at various points before birth-for example, fertilization, implantation, beginning of the third trimester in humans, or after birth, as can be seen in the effective age calculations for prematurely born babies (Hawkes, 2006). The point of birth that is culturally acknowledged adds further variation in the concept of birth.

Most definitions of death include cessation of breath and heartbeats, but arguments have made for different kinds of deaths, as not all organs in a body cease to function at the same time-for example, brain death. As in the case of life, the point of death that is culturally acknowledged can vary from a biological point of death. However, the range of variation in the beginning and ending points is small compared to the total length of life span.

As a group, primates show a strong tendency for increased longevity as a result of long gestation, long maturation, and long adulthood. Cross-species comparisons of life spans that are explained by biological variables such as brain size, body size, metabolic rate, and body temperature have yielded statistically significant relationships, which suggest that life span is an evolutionary variable that contributes to the fitness of a species. The maximum life spans of most mammalian species form a straight line when they are plotted against various biological variables. Human life span is not noteworthy, given that there are many other mammals, such as whales and elephants, with life spans as long as or longer than those of humans. While human life span falls within the expected range based on brain size, it is extraordinarily long for body size. However, the statistical nature of such studies should be kept in mind. Human life span comfortably exceeds 90 when looking at the species as a whole, after sampling millions of people; however, a random sample of a village population would more likely yield 60 or 70 years of average life span. In contrast, life span data for nonhumans are based on a very small sample. It is unknown how much of the life span differences are attributable to the extreme discrepancy in sample sizes (Overall, 2003).

Life span is related to, but different from, life expectancy, which is a hypothetical number derived from mortality tables. Life expectancy is the number of years that a cohort is expected to live. Life expectancy at a specific age is the average number of years the cohort (those born into a population at the same time) will live to be (Hurtado, 2000). Estimated life expectancy through human evolution has increased. Since it is impossible to get an accurate measurement of life expectancy, it is estimated ...