The biology of senescence

Abstract

The Measurement of senescence 1 24 33 Drosophila subobscura-hybrid vigour and longevity. Survival curves for the inbred lines B and K, and for the reciprocal hybrids between them 128 34 Survivorship curves for 82 males and 45 females of the black widow spider Latrodectes mactans 131 xii Illustrations 35 Survivorship, death and death-rate curves for the black widow. 36 Survivorship curves for male and female Tribolium madens 131 37 Effect of restricted food upon the longevity of Daphnia longispina 38 Effect of restricted food upon the duration of instars in Daphnia longispina 39 Effect of restricted food upon the rate of senile change in the heart rate of Daphnia longispina 40 Survival curves of normal and retarded male and female rats, showing the effect of dietary restriction 41 Neutral 1 7-Ketosteroids, 24-hour urinary excretion of human males 73 42 The postnatal growth in weight of male children 84 43 Annual growth increment in boys, from the data of Quetelet 65

Selection for life span in Drosophila melanogaster

“…Stocks were maintained separately for three or four generations at a density of more than 50 pairs per pint bottle and renewed at 10-14 days. To promote as extensive a variability as possible and following the methods of Lints and his coworkers (1974;1979), stocks were crossed such that each contributed equally in the creation of a four-way hybrid population. To permit the expression and equilibration of recombinants before selection, replicate lines of the hybrid population were then reproduced at 7-10 days for eight consecutive generations before selection was initiated.…”

“…While early experimental studies by Clark and Maynard Smith (1955) found heterosis in the longevity of outcrossed populations, other studies by Comfort (1979) have described the patterns that emerge from the comparison of life span in different organisms. Collectively, the many such life historical and genetic studies do generally establish the existence of the genetic control of longevity, but they provide little more than implication toward the fundamental question of evolutionary interest "How do long and short life spans evolve?…”

“…Delayed senescence, for example, should evolve when older individuals have an enhanced fitness because they can either produce greater numbers of progeny or provide an age-specific benefit to progeny. Also, repeated reproductions throughout a long life provide an effective counterbalance to a high juvenile mortality (Comfort, 1979;Schaffer, 1974;Murphy, 1968).…”

Cytogerontology since 1881: A reappraisal of August Weismann and a review of modern progress

“…During this time, various general theories as to the nature of the ageing process were put forward (for reviews see Medawar 1946 andComfort 1979), but these placed little emphasis on the influence of natural selection. Prominent among them were (i) the "optimistic studies" of Metchnikoff (1907) who sought to relate ageing to the influence of invading poisons, supposed to originate mainly from microbes in the gut; (ii) the view that ageing is related directly to growth, either through the differentiation of cells into terminal forms incapable of growth or repair (Minor 1907), or as a by-product of the continued action of the mechanism to limit growth as soon as specific size is reached (Bidder 1932)2; (iii) the hypothesis of Child (1915), based largely on extensive experimental research with planaria (Child 1911), that ageing is associated with a decrease in the rate of metabolism which results in the accumulation within the cell of "structural obstacles to metabolism" such as inactive wastes; and (iv) the "rate of living" theory of Pearl (1928), who proposed that the duration of life varies in inverse proportion to the rate of energy expenditure as a result of a finite total amount of "vitality" being used up.…”

“…Comfort 1979): "Death takes place because a worn-out tissue cannot for ever renew itself''. When read in context (see Section 2), it is clear that Weismann did not intend this sentence to have the circular meaning which seems so obvious when it is read by itself.…”