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The development of multicellular organisms involves a balance between somatic and reproductive tissues. This chapter outlines how the action of selection is influenced by the age at which structures and behaviours are expressed. This chapter's first section is called Reproductive allocation and it explains all about the correlated response to selection; antagonism of fitness components; the evolution of genetic correlation; and the optimal allocation. The second section, entitled Life histories, details selection in age-structured populations; depreciation of later reproduction; artificial selection for early reproduction; senescence; soma and germ; the nature of senescence; the evolution of senescence; selection for delayed senescence in Drosophila; endogenous evolution; and the disposable soma.

This chapter presents an interdisciplinary collaboration that has made scientific contributions to the emerging field of biodemography. It identities personal and professional challenges that emerge from collaborations in general and interdisciplinary research in particular. It then describes how researchers attempted to resolve these problems over the course of a collaboration that is long-term and ongoing.

This chapter examines the relationships between nutrition, life span, and sex. It considers the view that dietary restriction without severe malnutrition prolongs life. It is generally believed that the benefits of dietary restriction arise from eating fewer calories. However, Geometric Framework experiments on insects in which the effects of macronutrients have been separated indicate that, rather than calories, a key determinant of the relationship between diet and longevity is the balance of protein to nonprotein (fat and/or carbohydrate) energy in the diet. Meanwhile, the presumption in much of life history theory that life span and reproduction trade off against each other for limiting resources is shown to be too simplistic. These two life-history variables certainly have differing nutritional optima, but they can be dissociated and do not inevitably trade off. Reproductive senescence and aging may proceed at different rates in males and females, as predicted by sexual selection theory.

Guppy populations differ not only in their mating tactics but also in how they make their investment in reproduction. Life history traits such as age and size at maturity, number and size of offspring, vary markedly between populations. Much of this variation is a consequence of predation risk, but other environmental factors such as food availability, seasonality, fish density, and temperature are also important. This chapter explains why the Trinidadian system has proved an invaluable test of life history theory. It examines population differences in phenotypic plasticity and discusses age-related changes in reproductive behaviour. The consequences of key life history decisions for mating success in both males and females are also considered.

Cellular aging, commonly referred to as cellular senescence, is thought to be a ‘programmed’ cell fate in a similar sense that apoptosis is somehow programmed to happen to certain cells during development. A specific kind of aging called replicative senescence is characterized by a cell's permanent exit from the cell cycle after undergoing a certain number of divisions. One of the known causes of replicative senescence is telomere shortening after each division. Telomeres are the ends of linear eukaryotic chromosomes. This chapter discusses a model involving replicative senescence of cells lining the walls of blood vessels. Both a probabilistic model tracking individual cells and a deterministic model of the cell population dynamics are illustrated. Exercises are given at the end of the chapter.

The book illuminates the cluster of signs upon which the Victorians drew in order to derive meaning from the experience of growing old within a culture just beginning to take age into full account. The pictures of old age generated through fiction, journalism, science, and the fine arts reflected and shaped the quality of life for older people; they provided words and images which helped to form a conceptual basis for understanding ‘senescence’ as an integral phase of existence. The governing principle of the book is that frictions arose between elderly people whose numbers and needs taxed the state which sought to identify, classify, and provide for them. The book interprets these volatile relations as they appear in narrative form, social policy or cultural attitudes. It suggests that the terrors, anxieties and yearnings of old age as well as its pleasures and humors often exceed and challenge the emerging conventions.

Ample evidence from model organisms has indicated that subtle variation in genes can dramatically influence lifespan. The key genes and molecular mechanisms that have been identified so far encode for metabolism, maintenance, and repair mechanisms. This chapter provides an overview of genes and mechanisms that have been shown to regulate lifespan in model organisms. It limits the discussion to those genes that have human homologues, and explores whether and how these influence human lifespan and other life history traits.

Clinical, paleontologic, and ontogenetic data manifest that throughout the development of primates, morphogenesis is at all times closely related to the neurocranium and the face. Now, only in man can we find a hint to understanding the fundamental principle of cranial ontogenesis from the embryonic period to senescence. A comparative analysis of the data shows that a particular ontogenetic craniofacial diagnosis exists for each primate species. This mirrors a basic phenomenon known as craniofacial contraction, developed on the craniofacial biodynamics theory. This chapter discusses the biomechanical craniofacial relationships in living primates. Next, it will discuss the paleontologic applications and implications for comprehending the evolutionary process of hominoids.

The second chapter centers on novels by Naguib Mafouz, Alaa al-Aswany and Khalid Khalifa. The focus is on Cairo and Aleppo whose features are disappearing as a result of modernization, an anarchic urbanization, and demographic, political and social changes.In a new world, an elderly appearance in the street becomes synonymous with mockery, invisibility and erasure. The city is invaded by the new, and the old terrain of youth is gradually disappearing with the timeworn edifices peering through the cracks of modernity. The mutations taking place in the urban abode are synchronized with the alterations taking place within the physique of ageing individuals. The past remains predominant and is poignantly juxtaposed with the present, and the result is alienation and escape through memory.

This chapter presents works by Nazek Yared, Randa Khalidy and Abbas Baydun that, rather than focusing exclusively on public achievement, they present semi-autobiographical accounts. They are related by older individuals who focus on their personal idiosyncratic experiences of senescence, and aspects of their lives that have hitherto been overlooked. Their aim is to challenge erasure, re-evaluate their lives, make new decisions, concentrate on their daily quotidian lives and reveal their capacity for growth, even at a late age. Despite the inevitable movement towards a future in close proximity with death, the works are concerned with a revaluation of the past in its interaction with the present.

While the constellation of observed cognitive changes in advanced aging eludes a simple, parsimonious explanation, there is a recurring distinction between cognitive decline associated with executive and attention difficulties and that associated with declarative memory. This chapter discusses age-associated changes that affect the brain in the context of framing a general research approach to lifespan development. The discussion focuses on global measures of structural brain change, and distinct aging effects on frontal-striatal and medial temporal systems. These dissociable influences are explored as possible causes for why executive (attentional) dysfunction and declarative memory difficulties are so common in aging. The chapter also examines functional brain imaging methods that both illuminate detrimental functional consequences of brain aging and suggest functional responses that may be compensatory. The chapter concludes by considering brain aging within the broader context of lifespan development with a discussion of six possible ways early development can inform brain aging in senescence.

Before embarking on an ethical discussion, this chapter begins by distinguishing four possible outcomes of a biotechnological enhancement of the human lifespan – extended morbidity, compressed morbidity, decelerated senescence, and arrested senescence. The author summarises the major ethical arguments for and against effective substantial extension of the human lifespan through four categories: autonomy, beneficence (including non-maleficence), distributive justice, and meaning of life. The chapter explicates that decisions about priorities in medical and biotechnological research will have impacts on future generations. Society must be conscientious in its judgements about what is good for future people. The author argues that research on meanings of life, the value of old age, and a just and humane society requires approaches and methods fitting the subject of investigation, and in this area research confining itself to a ‘hard’ laboratory approach is often inappropriate.

This introductory chapter discusses the types of disturbance (natural, anthropogenic, allogenic, autogenic) caused by loss (or sometimes addition) of biomass or ecosystem function. Causes and characteristics of disturbances are also included, such as frequency, intensity, severity, extent, and disturbance interactions. It reviews the theories of disturbance ecology, especially on topics such as resistance, resilience, stability, and the intermediate disturbance hypothesis. Responses to disturbance include dispersal, establishment, and senescence of organisms as well as interactions among colonists of disturbed areas. Finally, it reviews ecological and economic benefits of disturbances providing an overview of the organization of the book.

This chapter uses Aubrey de Grey’s plan to end aging as an example of the radical enhancement of human life spans. I present the enterprise of radically extending human life spans as requiring an immoral transfer. The central characters in vampire stories achieve radically extended existences by draining the blood of victims. In this act, life force, or something similar, is transferred from the human victim to the vampire. The concept of life force has no place in modern biology and this means that radical human life extenders simply could not arrange its transfer from disempowered donors to empowered recipients. The empowered do nevertheless acquire something from the disempowered that has consequences similar to supping on their blood – this is their participation in dangerous clinical trials. The empowered will achieve their extended life spans by effectively taking years from others. The mechanism by which these years are transferred differs from that in vampire stories, but its consequences are the same.

At all taxonomic levels, there exists tremendous variation in life expectancy. A field mouse Peromyscus may live 1.2 years, while the African elephant may persist for 60 years, and even a mousesized bat such as Corynorhinus rafinesquei lives a healthy 20 years (Promislow 1991). Part of this variance is caused by differences in ecological risks, rodents being perhaps the most susceptible to predation, and to vagaries of climate and resources. Another portion is caused by differences in senescence, the intrinsic degeneration of function that produces progressive decrement in age-specific survival and fecundity. Senescence occurs in natural populations, where it affects life expectancy and reproduction as can be seen, for instance, from the progressive change in age-specific mortality and maternity of lion and baboon in East Africa. The occurrence of senescence and of the widespread variation in longevity presents a paradox: How does the age-dependent deterioration of fitness components evolve under natural selection? The conceptual and empirical resolutions to this problem will be explored in this chapter. We shall see that the force of natural selection does not weigh equally on all ages and that there is therefore an increased chance for genes with late-age-deleterious effects to be expressed. Life histories are expected to be optimized to regulate intrinsic deterioration, and in this way, longevity evolves despite the maladaptive nature of senescence. From this framework, we will then consider how the model is tested, both through studies of laboratory evolution and of natural variation, and through the physiological and molecular dissection of constraints underlying trade-offs between reproduction and longevity. As humans are well aware from personal experience, performance and physical condition progressively deteriorate with adult age. And in us, as well as in many other species, mortality rates progressively increase with cohort age. Medawar (1955), followed by Williams (1957), stated the underlying assumption connecting these events: Senescent decline in function causes a progressive increase in mortality rate. Although mortality may increase episodically across some age classes, such as with increases in reproductive effort, we assume that the continuous increase of mortality across the range of adult ages represents our best estimate of senescence.

Predation has been given many different definitions. For the purposes of this chapter, it is an interaction in which one free-living individual kills and derives resources from another organism. This definition includes finches that consume seeds but does not include fish that eat the siphons of clams that are unable to retract them quickly enough (assuming the clam usually survives the loss of tissue). Both broader and narrower definitions of predation are possible, and a variety can be found in ecology textbooks. Because broad definitions include herbivory and parasitism as forms of predation, the definition used here was chosen to minimize overlap with other chapters in this section. Predation probably arose early in the history of life, and since then, it has been a major source of natural selection on both parties in the interaction. Given the lethal consequences of predation, it is clear that predators will usually have some effect on the rate of increase of their prey. If prey differ in their susceptibility to predators due to heritable differences in characteristics, evolutionary change in antipredator traits will ensue. Because predators must consume prey to survive and reproduce, the selective importance of predation-related traits is obvious. Predators have undergone considerable change and diversification since the first predatory protocell evolved from what was probably a scavenging ancestor. Darwin regarded some of the clearest cases of natural selection as due to the interactions between predator and prey, and that viewpoint is also held by many current-day evolutionary biologists (e.g., Dawkins and Krebs 1979; Vermeij 1994). Predation can be regarded as the most basic interaction between populations. Herbivory and parasitism share the basic property of predation, that one organism consumes some or all of another living organism. Many cases of competition involve predation on the same set of prey species by two or more different predator species. Even when competitors consume nonliving foods, many aspects of the consumption process are similar to consumption of prey by predators. Even mutualism frequently involves one organism eating parts or products of another.

This chapter and the next focus on Goethe’s periodicals On Morphology for their paradigmatically neo-Lucretian treatment of biological life and its poetic documentation. In the morphology project, living beings are composite, equivocally generated forms whose vitality is coextensive with their transience; each “seeming individual”—not least the morphologist—is a fractious and plural “Being-Complex” whose incessant metamorphoses the science attempts to match with every available generic and figurative resource. This chapter argues that Goethe’s late work on metamorphosis shifts biology’s question from the problem of embryogenesis that drove its emergence as a science, toward neglected, late-life processes of senescence and decomposition. What might life look like, Goethe’s asks, from the perspective of the non-reproductive, but communicative, effluvia that mediate between beings in their transience? What arts of discomposure would be adequate to this view? Focusing on an experiment in which a mushroom draws its own image in spores, this chapter argues for the Romantic period credibility of nonhuman and non-verbal acts of semiosis and representation: “natural simulacra” that Goethe discovers in the botany of decay.