In this review paper formulas for survival functions are derived that take into account risks of deaths in early life including infancy, mid life, a random component of deaths due to accidents and deaths in older ages. The basic ideas used in the derivation of survival function for each of the components just mentioned are risk functions. Given a formula for a risk function, it is possible to derive a formula for the corresponding survival function. By using the theory of competing risks, a

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... ula for survival function that takes into account the risks of deaths in various stages of life expressed as a product of survival functions for the risks of deaths under consideration. For many applications information on the numerical values of parameters in survival functions is not available. Consequently, rationales are developed for assigning plausible values to parameters that take into account personal ideas of an investigator may have for each stage of life. For every assignment of parameter values in the paper, a numerical version of survival functions are plotted in graphs so that an assessment of the plausibility of the chosen parameter values may be made. Also included in the paper is an application of survival functions in an experiment to make an assessment as to whether a small population of chimpanzees, or some other endangered species of animals, will have descendants that make up a surviving population 200 years into the future.