LIFESPAN DEVELOPMENT

Lifespan Development

Lifespan Development

Introduction

Life span 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 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. The point of birth that culturally acknowledged adds further variation in the concept of birth.

Discussion

Most definitions of death include cessation of breath and heartbeats, but arguments 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 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.

It thought that maximum life span biologically determined and not variable. The maximum life span can be empirically noted by observing the longest survival of an individual member of a species, which provides the minimum threshold of the maximum life span. This is a difficult challenge for studying long-lived organisms such as humans, since researchers do not outlive the subjects and cannot record births and deaths. Researchers have to rely on records and age estimations. Living to the age of 100 is unlikely for humans, but not rare: About 7 in 1,000 people estimated to reach the centenarian milestone. Beyond 100, surviving each additional year is subject to a 50% probability.

The maximum human life span estimated to be between 115 and 150 years, with the longest-lived human on record having lived 122 years (died in 1997). The majority of centenarians are women, and most of the oldest old are women. Reasons for sex differences in life span are not clear, although many have attributed it to greater testosterone-driven mortality in males.

As a group, primates show a strong tendency for increased life span as a result of long gestation, long maturation, and long adulthood. Cross-species comparisons of life spans that explained by biological variables such as brain size, body size, metabolic rate, and body temperature have yielded statistically significant relationships (Cutler, 1975; Sacher, 1978), which suggest that life span is an evolutionary variable that contributes to the fitness of a species.

he maximum life spans of most mammalian species form a straight line when they 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 (Hill, 1993).

However, the statistical nature of such studies should be kept in ...