Setting the stage: the history, chemistry, and geobiology behind RNA

No community-accepted scientific methods are available today to guide studies on what role RNA played in the origin and early evolution of life on Earth. Further, a definition-theory for life is needed to develop hypotheses relating to the "RNA First" model for the origin of life. Four approaches are currently at various stages of development of such a definition-theory to guide these studies. These are (a) paleogenetics, in which inferences about the structure of past life are drawn from the structure of present life; (b) prebiotic chemistry, in which hypotheses with experimental support are sought that get RNA from organic and inorganic species possibly present on early Earth; (c) exploration, hoping to encounter life independent of terran life, which might contain RNA; and (d) synthetic biology, in which laboratories attempt to reproduce biological behavior with unnatural chemical systems.     

Pluralism or unity in biology: could microbes hold the secret to life?

Pluralism is popular among philosophers of biology. This essay argues that negative judgments about universal biology, while understandable, are very premature. Familiar life on Earth represents a single example of life and, most importantly, there are empirical as well as theoretical reasons for suspecting that it may be unrepresentative. Scientifically compelling generalizations about the unity of life (or lack thereof) must await the discovery of forms of life descended from an alternative origin, the most promising candidate being the discovery of extraterrestrial life. Nonetheless, in the absence of additional examples of life, we are best off exploring the microbial world for promising explanatory concepts, principles, and mechanisms rather than prematurely giving up on universal biology. Unicellular microbes (especially prokaryotes) are by far the oldest, metabolically most diverse, and environmentally tolerant form of life on our planet. Yet somewhat ironically, much of our theorizing about life still implicitly privileges complex multicellular eukaryotes, which are now understood to be highly specialized, fragile latecomers to Earth. The problem with pursuing a pluralist approach to understanding life is that it is likely to blind us to the significance of just those entities and causal processes most likely to shed light on the underlying nature of life.     

Trematode life cycles: short is sweet?

Complex life cycles are a hallmark of parasitic trematodes. In several trematode taxa, however, the life cycle is truncated: fewer hosts are used than in a typical three-host cycle, with fewer transmission events. Eliminating one host from the life cycle can be achieved in at least three different ways. Some trematodes show even more extreme forms of life cycle abbreviations, using only a mollusc to complete their cycle, with or without sexual reproduction. The occurrence of these phenomena among trematode families are reviewed here and show that life cycle truncation has evolved independently many times in the phylogeny of trematodes. The hypotheses proposed to account for life-cycle truncation, in addition to the factors preventing the adoption of shorter cycles by all trematodes are also discussed. The study of shorter life cycles offers an opportunity to understand the forces shaping the evolution of life cycles in general.     

Environmental restraints and life strategies: a habitat templet matrix

Summary Four basic environmental restraints on life are deduced from the requirements of life's inherent order laws. Possible life strategies to contend with these restraints are listed. The various combinations of the restraints are subsequently investigated, and appropriate combinations of life strategies are fitted. This model is finally tested against insect case histories in various environments, and is demonstrated to explain some combinations of characteristics of insects in ecosystems not covered by the r-K or r-K-A continua. The role of heterochrony in achieving appropriate life strategies is briefly discussed.     

动物生活史进化理论研究进展

综述了生活史性状、生活史对策、权衡、适合度及进化种群统计学等动物生活史进化领域的进展。权衡是生活史性状之间相互联系的纽带,分为生理权衡与进化权衡。适合度是相对的,与个体所处的特定环境条件有关,性状进化与适合度之间关系紧密。适合度是生活史进化理论研究的焦点。探讨动物生活史对策的理论很多,影响最大的是MacArthur和Wilson提出的r对策及K对策理论。随年龄的增长,动物存活率及繁殖率逐步下降的过程,称为衰老;解释衰老的进化理论主要有突变-选择平衡假设和多效对抗假设。进化种群统计学将种群统计学应用于生活史进化研究,为探讨表型适合度的进化提供了有效的手段。将进化种群统计学、数量遗传学及特定种系效应理论进行整合,建立完整的动物生活史进化综合理论体系,是当代此领域的最大挑战。     

The Soft Underbelly of Evolution?

Evolution and the origin of life are separate, if connected, topics, but they are frequently conflated??especially by creationists. Regarding the natural origin of life as ??the soft underbelly?? of evolution, creationists argue that it is impossible, improbable, or insusceptible to scientific investigation. Underlying their arguments is the hope that the failure of scientific research on the origin of life is evidence for a supernatural account. It is crucial for teachers to understand the nature of science in order to be able to explain why appeals to the supernatural are out of place in explaining the origin of life and why scientific research on the origin of life is not intrinsically a threat to faith.     

"New beginnings": a case study in gay men's changing perceptions of quality of life during the course of HIV infection

This article reports results of an ethnographic study that sought to understand how a cohort of gay men living with HIV infection evaluated and worked to preserve or improve the quality of their lives. Themes of life story narratives are identified, each with an associated stylistic self-orientation to living with HIV infection. Changes in thematic content of a selected participant's life story narratives are discussed, demonstrating how events of his daily life are integrated into the narratives. Resultant concurrent shifting of themes and stylistic orientations is linked to his perception of improved quality of life.     

Organization of vertebrate annual cycles: implications for control mechanisms

The majority of vertebrates have a life span of greater than one year. Therefore individuals must be able to adapt to the annual cycle of changing conditions by adjusting morphology, physiology and behaviour. Phenotypic flexibility, in which an individual switches from one life history stage to another, is one way to maximize fitness in a changing environment. When environmental variation is low, few life history stages are needed. If environmental variation is large, there are more life history stages. Each life history stage has a characteristic set of sub-stages that can be expressed in various combinations and patterns to determine state at any point in the life of the individual. Thus individuals have a finite number of states that can be expressed over the spectrum of environmental conditions in their life spans. Life history stages have three phases-development, mature capability (when characteristic sub-stages can be expressed) and termination. Expression of a stage is time dependent (probably a minimum of one month), and termination of one stage overlaps development of the next stage. It follows that the more life history stages an individual expresses, the less flexibility it will have in timing those stages. Having fewer life history stages increases flexibility in timing, but less tolerance of variation in environmental conditions. To varying degrees it is possible to overlap mature capability of some life history stages to effectively reduce 'finite stage diversity' and maximize flexibility in timing. Theoretical ways by which this can be done, and the implications for neuroendocrine and endocrine control mechanisms are discussed. Twelve testable hypotheses are posed that relate directly to control mechanisms.     

常见寿命数据类型及生命表的编制方法

生命表是描述种群死亡过程的有用工具,介绍了4种常见的寿命数据类型;寿终数据,右删失数据,左删失数据和区间型数据特征及其相应的数据分析处理方法即生命表法,乘积限估计和Turbull估计法,对生命表法和乘积限估计法应用上的特点进行了比较,同时还对特殊的寿命数据类型－－截断数据做了简要介绍。     

How perennial are perennial plants?

Trade-offs involving life span are important in the molding of plant life histories. However, the empirical examination of such patterns has so far been limited by the fact that information on life span is mainly available in terms of discrete categories; annuals, semelparous perennials and iteroparous perennials. We used transition matrix models to project continuous estimates of conditional life spans from published information on size- or stage-structured demography for 71 perennial plant species. The projected life span ranged from 4.3 to 988.6 years and more than half of the species had a life span of more than 35 years. Woody plants had on average a projected life span more than four times as long as non-woody plants. Life spans were higher in forests than in open habitats and individuals of non-clonal species tended to have a longer life span than ramets of clonal species. Self-incompatible plants on average lived longer than self-compatible plants. There were no clear relations between life span and geographical region, dispersal syndrome, pollination mode, seed size or the presence of a seed bank. We conclude that accurate estimates of life span are central to understand how longevity is correlated to other traits within the group of perennial plants.     

Complex life cycles drive community assembly through immigration and adaptive diversification

Most animals undergo ontogenetic niche shifts during their life. Yet, standard ecological theory builds on models that ignore this complexity. Here, we study how complex life cycles, where juvenile and adult individuals each feed on different sets of resources, affect community richness. Two different modes of community assembly are considered: gradual adaptive evolution and immigration of new species with randomly selected phenotypes. We find that under gradual evolution complex life cycles can lead to both higher and lower species richness when compared to a model of species with simple life cycles that lack an ontogenetic niche shift. Thus, complex life cycles do not per se increase the scope for gradual adaptive diversification. However, complex life cycles can lead to significantly higher species richness when communities are assembled trough immigration, as immigrants can occupy isolated peaks of the dynamic fitness landscape that are not accessible via gradual evolution.     

肺癌生存质量量表在晚期肺癌中使用的研究进展

近几年来,肺癌的发病率呈现逐年上升的趋势,成为癌症中的头号杀手。临床上针对不同类型肺癌有不同的治疗策略,由于临床上大部分病人在确诊为肺癌时已经为晚期,对于常规治疗方法难以达到效果时,关注肺癌患者的生存质量就显地尤为必要。肺癌生存质量量表可以反映病人临床治疗后的生存质量状况,达到反馈治疗效果的目的。在临床实验中使用肺癌生存质量量表可以帮助临床医师制定最优化的治疗方案。国际上的研究大多不是以生存质量为主要终点的研究,生存质量也不能全面的反映病人预后的状况,希望在今后的研究中,肺癌生存质量量表能够在临床中的使用更加普及、更加全面。本文就肺癌生存质量量表在晚期肺癌中使用的研究进展作一综述,以期更加促进我们对于晚期肺癌患者生存质量的思考与关注,更有利于适合我国国情的生存质量量表的研究和发展。     

Negative Life Events Vary by Neighborhood and Mediate the Relation between Neighborhood Context and Psychological Well-Being

Researchers have speculated that negative life events are more common in troubled neighborhoods, amplifying adverse effects on health. Using a clustered representative sample of Chicago residents (2001–03; n = 3,105) from the Chicago Community Adult Health Survey, we provide the first documentation that negative life events are highly geographically clustered compared to health outcomes. Associations between neighborhood context and negative life events were also found to vary by event type. We then demonstrate the power of a contextualized approach by testing path models in which life events mediate the relation between neighborhood characteristics and health outcomes, including self-rated health, anxiety, and depression. The indirect paths between neighborhood conditions and health through negative life event exposure are highly significant and large compared to the direct paths from neighborhood conditions to health. Our results indicate that neighborhood conditions can have acute as well as chronic effects on health, and that negative life events are a powerful mechanism by which context may influence health.     

Disentangling the Evolution of Early and Late Life History Traits in Humans

Some aspects of human life history are unique among primates. Most notably, humans have a younger weaning age, a later age at first parturition, a shorter female reproductive period, and a longer lifespan than other living hominoid species. Obtaining a better understanding of when and how life history changed during human evolution is important to those studying the evolutionary developmental biology of extinct hominins, as life history traits pace developmental processes. Life history traits are thought to be linked via tradeoffs, such that changes in early life history traits directly affect those that follow later in life, and vice versa. However, it is also worth considering how changes to a single life history trait may indirectly affect other traits by way of modifying selective pressures acting on individuals and groups. For example, because they affect the size and demographic structure of a group, late life history traits (e.g., lifespan) may also affect the evolution of life history traits that occur earlier in life, but by modifying selective pressures acting on juveniles rather than by triggering a physiological tradeoff. This review marks an effort to begin to disentangle the ways in which early and late life history traits may affect each other both directly and indirectly. We concentrate on female life history characteristics. First, we review previous research on the evolution of the postmenopausal lifespan in women. Next we discuss recent findings concerning the relationship between the optimal length of the female reproductive period, mortality, and weaning age that show that selection favors a shorter female reproductive period in the presence of a younger weaning age. We discuss the implications this finding holds for understanding the evolution of life history traits that are of particular interest to developmental biologists.     

Oviposition Site Choice and Life History Evolution

SYNOPSIS. Studies of life history evolution, as well as muchof life history theory, have typically focused on "hard" componentsof life histories; phenotypic characteristics that can be readilyobserved, quantified, and ultimately, connected rather directlyto fitness. Typical of these are propagule size, propagule number,and age and size at maturity. What is largely missing from thestudy of life history evolution is consideration of the roleof behavior, principally female oviposition site choice, inthe evolution of life histories. For oviparous organisms, naturalselection cannot produce locally optimized "hard" componentsof life history phenotypes without a consistent environmentalcontext (whether invariant orvariable); in a variable environment,that consistent environmental context can be most effectivelyprovided by interactive oviposition site choice. I present amodel of selection on oviposition site choice in the contextof the evolution of "hard" components of life history phenotypes,along with some experimental data illustrating oviposition sitechoice in response to predators. The model and data are thenrelated to the overall question of the role of oviposition sitechoice in life history evolution. The conclusion is that ovipositionsite choice must be under equally strong selection with eggsize, egg number and the other hard components of life historiesin order to generate and optimize locally adapted or ecologicallyspecialized life history phenotypes, and must therefore, playa significant role in the evolution of life histories.     

Life style — An emergent concept in the sociomedical sciences

The concept of life style recently has gained prominence in sociomedical research; yet the term remains poorly defined. This paper traces the evolution of the life style concept from its origins in sociological and personality studies to its current use in reference to behavioral risk factors for disease. Particular attention is given to the changes in meaning that have taken place over the past few decades. Similarities between the notion of life style and concepts of cultural integration are noted, and the various uses of life style are categorized along an idealist-materialist continuum. Finally, the authors fault medicalized notions of life style for failing to acknowledge the importance of the context and meaning of health-related behavior.     

Synthetic Biology and the Moral Significance of Artificial Life: A Reply to Douglas,Powell and Savulescu

I discuss the moral significance of artificial life within synthetic biology via a discussion of Douglas, Powell and Savulescu's paper 'Is the creation of artificial life morally significant’. I argue that the definitions of 'artificial life’ and of 'moral significance’ are too narrow. Douglas, Powell and Savulescu's definition of artificial life does not capture all core projects of synthetic biology or the ethical concerns that have been voiced, and their definition of moral significance fails to take into account the possibility that creating artificial life is conditionally acceptable. Finally, I show how several important objections to synthetic biology are plausibly understood as arguing that creating artificial life in a wide sense is only conditionally acceptable.     

Diet as a modulator of aging and longevity.

The interrelationships between diet and life span are reviewed, with emphasis on results obtained in studies with experimental animals. Ad libitum feeding throughout life does not promote maximal survival and food restriction increases mean life span. The possible importance of total energy, carbohydrate, and protein intake are considered, as well as the influence of mode of feeding. A number of mechanisms that might explain how nutrition affects life span are discussed, including disease pattern, free radicals, neuroendocrine system, and protein turnover. The significance of these findings in relation to the health and life span of human subjects is not known and deserves further exploration. However, they emphasize the importance of diet as a tool to help explore the biochemical and physiological basis for aging in animal models.     

Retired flies,hidden plateaus,and the evolution of senescence in Drosophila melanogaster

Late‐life plateaus in age‐specific mortality have been an evolutionary and biodemographic puzzle for decades. Although classic theory on the evolution of senescence predicts late‐life walls of death, observations in experimental organisms document the opposite trend: a slowing in the rate of increase of mortality at advanced ages. Here, I analyze published life‐history data on individual Drosophila melanogaster females and argue for a fundamental change in our understanding of mortality in this important model system. Mortality plateaus are not, as widely assumed, exclusive to late life, and are not explained by population heterogeneity—they are intimately connected to individual fecundity. Female flies begin adult life in the working stage, a period of active oviposition and low but accelerating mortality. Later they transition to the retired stage, a terminal period characterized by limited fecundity and relatively constant mortality. Because ages of transition differ between flies, age‐synchronized cohorts contain a mix of working and retired flies. Early‐ and mid‐life plateaus are obscured by the presence of working flies, but can be detected when cohorts are stratified by retirement status. Stage‐specificity may be an important component of Drosophila life‐history evolution.     

Towards a general perspective on life‐history evolution and diversification in parasitoid wasps

In attempting to explain the marked interspecific variation evident in many components of life‐history in parasitoid wasps, biologists have sought to identify general predictors of suites of ‘important’ life‐history traits. Two predictors currently in general use are: (1) the parasitoid mode of larval development in relation to future host growth and development [no further host growth and development (= idiobiosis) versus continued host growth and development (= koinobiosis)]; and (2) the ovigeny index (the degree to which the lifetime potential complement of eggs is mature at the start of adult life in females). These have been postulated to share several life‐history correlates, and an earlier comparative analysis showed the predictors to be associated. Two questions are thus posed: which life‐history variables are actually common to both idio/koinobiosis and the ovigeny index, and which are responsible for the link between these two axes of life‐history diversity? Through comparative analyses of a database of life‐history traits for 133 parasitoid wasp species, four life‐history correlates out of the 11 we investigated are shown to account for the association between the two predictors: the relative level of resource investment per egg (degree of yolk richness, which is lower in koinobionts), pre‐adult lifespan (longer in koinobionts), female lifespan (shorter in koinobionts), and maximum egg load (larger in koinobionts). Our findings pave the way for full integration of the dichotomous hypothesis with the ovigeny index hypothesis, to provide a holistic perspective on parasitoid wasp life‐history diversity and evolution. © 2011 The Linnean Society of London, Biological Journal of the Linnean Society, 2011, 104 , 443–461.