. The biology of senescence. Old age; Aging; Longevity. The Nature and Criteria of Senescence metrical progression (Wiesner and Sheard, 1934). Real survival graphs are commonly intermediate in form between the two ideal contours. Pearl and Miner (1935) distinguished three main types of observed death-curve, varying in skewness from the nearly rectangular in organisms with a low standing death- rate throughout life, but showing a tendency to die almost simultaneously in old age, to the logarithmic decline char- acteristic of populations which show no senescence, or which die out before it can b
. The biology of senescence. Old age; Aging; Longevity. The Nature and Criteria of Senescence metrical progression (Wiesner and Sheard, 1934). Real survival graphs are commonly intermediate in form between the two ideal contours. Pearl and Miner (1935) distinguished three main types of observed death-curve, varying in skewness from the nearly rectangular in organisms with a low standing death- rate throughout life, but showing a tendency to die almost simultaneously in old age, to the logarithmic decline char- acteristic of populations which show no senescence, or which die out before it can become evident (Fig. 6). A fourth theoret- ical type, in which the curve is rectangular but inverse to that. TIME Fig. 5. (a)—Survival curve at a constant rate of mortality (50 per cent per unit time). TIME Fig. 5 (b).—Survival curve of a population which exhibits sene- scence. found in the ideal senescent population, was recognized by Pearl (1940) as a theoretical possibility; it seems to be realized in nature among organisms which have a high infant mortality, but whose expectation of life increases over a long period with increasing age. This pattern of survival is characteristic of some trees (Szabo, 1931) but probably also occurs in animals. 'There may be animals in which the expectation of life increases con- tinuously with age. This may be so for many fish under natural conditions. It certainly goes on increasing for a considerable time. Thus in a species where the expectation of life was equal to the age, or better, to the age plus one week, no members would live for ever, but a small fraction would live for a very long time. A centenarian aware of the facts would pity a child, with an expectation of life of only a few years, but would envy a bicentenarian' (Haldane, 1953). G 19. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectl
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Keywords: ., bookcentury1900, booksub, booksubjectlongevity, booksubjectoldage
