scholarly journals On fitness and the cost of natural selection

1967 ◽  
Vol 9 (1) ◽  
pp. 1-15 ◽  
Author(s):  
William Feller
Keyword(s):  
Steady State ◽  
Natural Selection ◽  
Population Size ◽  
Relative Frequency ◽  
Cumulative Effect ◽  
Relative Fitness ◽  
Individual Species ◽  
Theory Of Evolution ◽  
The Absolute ◽  
The Cost

A Mendelian population without artificial external constraints does in general not increase at a constant rate. Formulas neglecting the changes in population size introduce an error which is negligible under ordinary circumstances but whose cumulative effect over long periods may be disastrous. Questions relating to the cost of natural selection, the nature of an unstable equilibrium, the survival of genes, etc. cannot be treated without regard to absolute population sizes. The limitation of the notion of relative fitnesses is illustrated by the fact that in some typical situations the survival of the a-gene depends only on the absolute fitness of the Aa-heterozygote, but not on the fitnesses of the homozygotes. Furthermore, a decrease of the (absolute or relative) fitness of one genotype may actually increase the viability of the population and its ultimate size.Even when the relative frequency qn of the a-gene tends to zero the absolute number of such genes may increase from generation to generation at a geometric rate. Therefore the circumstance that qn → 0 may be insignificant as compared to the fact that the earth cannot sustain an infinitely increasing population. Ultimately the population size is bound to influence the environment and so the fitnesses will change. Thus we must consider density-dependent fitnesses and then observed fitnesses cannot be used to predict the ultimate fate of a population. It is now known (Dobzhansky, 1965) that relative fitnesses are sometimes very sensitive to small changes in environment and that the same species may occupy a great variety of environmental niches. It is therefore quite likely that at least part of a population will find itself in a modified environment before too many generations have passed. For the evolution of a species and the development of new forms it is then not important that under fixed conditions the relative frequency qn of the a-gene would tend to zero. The problem is whether the actual number of such genes will increase for a period sufficiently long to encounter changed conditions or to establish itself in new combinations. This question is significant because the convergence of the frequencies qn to zero may be extremely slow. Thus even in a population of fixed size a disappearing gene could exist long enough to contribute to evolutionary processes.Speaking generally, the thinking in terms of an assumed steady state and relative fitnesses seems to aggravate the problem of applying the wonderful results of modern genetics to the theory of evolution. For example, various mechanisms which are often considered as eliminating genetic variability may sometimes produce the opposite effect. The theory of evolution should distinguish between what the physicist would call macroscopic and microscopic equilibrium. Even if the world as we see it were in a perfect equilibrium this would not imply an approximate steady state for individual species, not to speak of genes. It is clear that an evolution to higher forms depends on a frequent decrease in fertility rates. If one considers slow changes rather than an unattainable steady state then a loss of fitness may be beneficial in the long run and contribute to genetic variety.

scholarly journals When good mutations go bad: how population size can change the direction of natural selection

2021 ◽  
Author(s):  
Yevgeniy Raynes ◽  
Christina L Burch ◽  
Daniel M Weinreich
Keyword(s):  
Natural Selection ◽  
Population Size ◽  
Underlying Mechanism ◽  
Deleterious Mutations ◽  
Fitness Costs ◽  
Sign Inversion ◽  
Population Sizes ◽  
The Common ◽  
Fitness Benefits ◽  
The Cost

Classical evolutionary theory holds that the efficiency, but not the direction, of natural selection depends on population size. In small populations, drift overwhelms selection, rendering all fitness-affecting mutations selectively neutral. Yet, beneficial mutations never become deleterious and deleterious mutations never become beneficial. Remarkably, several mutations, including in modifiers of recombination and mutation rate, have now been shown to be favored at some population sizes but disfavored at others, challenging established theory. Previously, we have designated this phenomenon sign inversion. Here we show that, unlike selected mutations in the classical framework, mutations susceptible to sign inversion confer both fitness costs and fitness benefits, that vary among their carriers. Furthermore, all such mutations can be classified based on whether their effects differ between or within mutant lineages. Using computer simulations, we demonstrate that both between-lineage and within-lineage variability can cause sign inversion and elucidate the common underlying mechanism. Our results confirm that variability in the sign of selective effects is necessary for sign inversion, which occurs because drift overwhelms selection on carriers bearing the cost and carriers enjoying the benefit at different population sizes.

scholarly journals Evolutionary rescue and the limits of adaptation

2013 ◽  
Vol 368 (1610) ◽  
pp. 20120080 ◽  
Author(s):  
Graham Bell
Keyword(s):  
Genetic Variation ◽  
Natural Selection ◽  
Relative Fitness ◽  
Population Declines ◽  
Genetic Constraints ◽  
Evolutionary Rescue ◽  
Large Populations ◽  
Effective Selection ◽  
The Cost ◽  
Number Of Individuals

Populations subject to severe stress may be rescued by natural selection, but its operation is restricted by ecological and genetic constraints. The cost of natural selection expresses the limited capacity of a population to sustain the load of mortality or sterility required for effective selection. Genostasis expresses the lack of variation that prevents many populations from adapting to stress. While the role of relative fitness in adaptation is well understood, evolutionary rescue emphasizes the need to recognize explicitly the importance of absolute fitness. Permanent adaptation requires a range of genetic variation in absolute fitness that is broad enough to provide a few extreme types capable of sustained growth under a stress that would cause extinction if they were not present. This principle implies that population size is an important determinant of rescue. The overall number of individuals exposed to selection will be greater when the population declines gradually under a constant stress, or is progressively challenged by gradually increasing stress. In gradually deteriorating environments, survival at lethal stress may be procured by prior adaptation to sublethal stress through genetic correlation. Neither the standing genetic variation of small populations nor the mutation supply of large populations, however, may be sufficient to provide evolutionary rescue for most populations.

scholarly journals Adaptive ageing theory of faster adaptation and inconsistency of the conventional selection shadow evolutionary theory of ageing.

2020 ◽  
Author(s):  
Arsen Korpetayev
Keyword(s):  
Dna Repair ◽  
Natural Selection ◽  
Population Size ◽  
Selection Pressure ◽  
Bowhead Whale ◽  
Ecological Niches ◽  
Reproduction Rate ◽  
Conventional Theory ◽  
Theory Of Evolution ◽  
Optimal Population

Selection shadow has been the conventional theory of evolution of ageing for decades. I argue that selection shadow is merely a phenomenon by which deleterious mutation will be inevitably passed on if they manifest only after mating. However, to explain prevalence of ageing, the authors of the conventional theory erroneously equated passing on and persistence by interpreting selection shadow as if “selection pressure is decreased after mating” and for the same reason assumed that ageing is deleterious1,2. In their conventional framework, although ageing is assumed to be deleterious, it is immune to natural selection, due to happening after mating i.e. being in the selection shadow. In reality selection pressure still remains after mating in form of the need to feed offspring and so also in form of inter- and intraspecies competition and predation avoidance etc. I show that the conventional selection shadow theory is therefore inconsistent, since shadowed counteracting “positive” mutations will inevitably pass with “negative” mutations, resulting in individuals that do not age. And so, since ageing is assumed to be deleterious in this conventional framework, inevitable non-ageing individuals will outcompete ageing ones in intra- and interspecies competition for similar ecological niches. This way the inconsistency of the conventional theory of selection shadow predicts that non-ageing organisms will prevail, which is not what we observe. Recently, some articles incline towards adaptive theory of ageing i.e. ageing as an advantageous mechanism. However, the ground of such inclination has mostly been reduced competition for food and space between parents and offsprings3,4. I show that ageing allows for increased reproduction rate, while maintaining optimal population size. As a result of promoted reproduction rate, rate of introduced germline mutations is increased, which means faster adaptation. Faster adapting ageing individuals outcompete non-ageing slower adapting individuals that occupy similar ecological niches, inter and intraspecies. Therefore, since ageing is obviously advantageous, this means that all experimental evidence that supported selection shadow theory of ageing5–9, also support the proposed adaptive theory of faster adaptation, the difference is interpretation: investigated pleiotropic muta-tions are not antagonistic after all, and mutation accumulation actually accumulates positive germline ageing mutations. Based on genome analysis10 of the longest living mammal – bowhead whale, I also propose that mutations in DNA repair proteins are a mechanism to tune ageing by natural selection when optimal population size is changed by long lasting shifts in ecosystem, such as new food source. I suggest that DNA repair complexes are purposely of lowered fidelity to allow for somatic mutations to accumulate and so to increase deathrate by ageing leading to faster adaptation.

Theorems of Natural Selection: Results of Price, Fisher, and Robertson

2018 ◽  
Author(s):  
Bruce Walsh ◽  
Michael Lynch
Keyword(s):  
Natural Selection ◽  
Fundamental Theorem ◽  
Selection Response ◽  
Relative Fitness ◽  
Additive Variance ◽  
Change In The Mean ◽  
Important Exception ◽  
The Mean ◽  
The Cost ◽  
Fisher’S Fundamental Theorem

This chapter reviews a number of “theorems” of natural selection. These include exact results (true mathematical theorems): the Robertson-Price identity, Price's general expression for any form of selection response, and the Fisher-Price-Ewens version of Fisher's fundamental theorem. Their generality comes as the cost of usually being very difficult to apply. An important exception is the Robertson-Price identity, which expresses the within-generation change in the mean of a trait as its covariance with relative fitness. This chapter also examines three classic approximations: Fisher's fundamental theorem for the behavior of mean population fitness, and Robertson's secondary theorem and the breeder's equation for the expected response in a trait under selection, showing both how these results are connected and the error given by the various approximations. Finally, the chapter examines the connection between the additive variance of a trait and its correlation with fitness.

Darwinian Evolutionary Theory

2018 ◽  
Author(s):  
Michael Ruse
Keyword(s):  
Sexual Selection ◽  
Natural Selection ◽  
Middle Class ◽  
Evolutionary Theory ◽  
Scientific Community ◽  
Homo Sapiens ◽  
Origin Of Species ◽  
Theory Of Evolution ◽  
Descent Of Man

Charles Robert Darwin, the English naturalist, published On the Origin of Species in 1859 and the follow-up work The Descent of Man in 1871. In these works, he argued for his theory of evolution through natural selection, applying it to all organisms, living and dead, including our own species, Homo sapiens. Although controversial from the start, Darwin’s thinking was deeply embedded in the culture of his day, that of a middle-class Englishman. Evolution as such was an immediate success in scientific circles, but although the mechanism of selection had supporters in the scientific community (especially among those working with fast-breeding organisms), its real success was in the popular domain. Natural selection, and particularly the side mechanism of sexual selection, were known to all and popular themes in fiction and elsewhere.

scholarly journals Large numbers of vertebrates began rapid population decline in the late 19th century

2016 ◽  
Vol 113 (49) ◽  
pp. 14079-14084 ◽  
Author(s):  
Haipeng Li ◽  
Jinggong Xiang-Yu ◽  
Guangyi Dai ◽  
Zhili Gu ◽  
Chen Ming ◽  
...  
Keyword(s):  
Genetic Diversity ◽  
Population Size ◽  
Threatened Species ◽  
Driving Forces ◽  
Population Decline ◽  
Cumulative Effect ◽  
Extinction Time ◽  
Time Period ◽  
Large Numbers ◽  
The Difference

Accelerated losses of biodiversity are a hallmark of the current era. Large declines of population size have been widely observed and currently 22,176 species are threatened by extinction. The time at which a threatened species began rapid population decline (RPD) and the rate of RPD provide important clues about the driving forces of population decline and anticipated extinction time. However, these parameters remain unknown for the vast majority of threatened species. Here we analyzed the genetic diversity data of nuclear and mitochondrial loci of 2,764 vertebrate species and found that the mean genetic diversity is lower in threatened species than in related nonthreatened species. Our coalescence-based modeling suggests that in many threatened species the RPD began ∼123 y ago (a 95% confidence interval of 20–260 y). This estimated date coincides with widespread industrialization and a profound change in global living ecosystems over the past two centuries. On average the population size declined by ∼25% every 10 y in a threatened species, and the population size was reduced to ∼5% of its ancestral size. Moreover, the ancestral size of threatened species was, on average, ∼22% smaller than that of nonthreatened species. Because the time period of RPD is short, the cumulative effect of RPD on genetic diversity is still not strong, so that the smaller ancestral size of threatened species may be the major cause of their reduced genetic diversity; RPD explains 24.1–37.5% of the difference in genetic diversity between threatened and nonthreatened species.

scholarly journals A Cost Analysis of School-Based Lifestyle Interventions

2018 ◽  
Vol 19 (6) ◽  
pp. 716-727 ◽  
Author(s):  
Marije Oosterhoff ◽  
Hans Bosma ◽  
Onno C.P. van Schayck ◽  
Manuela A. Joore
Keyword(s):  
Physical Activity ◽  
Steady State ◽  
Primary School ◽  
Relative Effectiveness ◽  
First Year ◽  
Lifestyle Interventions ◽  
Stakeholder Perspectives ◽  
School Based ◽  
The Cost ◽  
Cost Offsets

Abstract A uniform approach for costing school-based lifestyle interventions is currently lacking. The objective of this study was to develop a template for costing primary school-based lifestyle interventions and apply this to the costing of the “Healthy Primary School of the Future” (HPSF) and the “Physical Activity School” (PAS), which aim to improve physical activity and dietary behaviors. Cost-effectiveness studies were reviewed to identify the cost items. Societal costs were reflected by summing up the education, household and leisure, labor and social security, and health perspectives. Cost inputs for HPSF and PAS were obtained for the first year after implementation. In a scenario analysis, the costs were explored for a hypothetical steady state. From a societal perspective, the per child costs were €2.7/$3.3 (HPSF) and €− 0.3/$− 0.4 (PAS) per day during the first year after implementation, and €1.0/$1.2 and €− 1.3/$− 1.6 in a steady state, respectively (2016 prices). The highest costs were incurred by the education perspective (first year: €8.7/$10.6 (HPSF) and €4.0/$4.9 (PAS); steady state: €6.1/$7.4 (HPSF) and €2.1/$2.6 (PAS)), whereas most of the cost offsets were received by the household and leisure perspective (first year: €− 6.0/$− 7.3 (HPSF) and €− 4.4/$− 5.4 (PAS); steady state: €− 5.0/$− 6.1 (HPSF) and €− 3.4/$− 4.1 (PAS)). The template proved helpful for costing HPSF and PAS from various stakeholder perspectives. The costs for the education sector were fully (PAS) and almost fully (HPSF) compensated by the savings within the household sector. Whether the additional costs of HPSF over PAS represent value for money will depend on their relative effectiveness.

scholarly journals Research on Cooperative Innovation Behavior of Industrial Cluster Based on Subject Adaptability

2016 ◽  
Vol 2016 ◽  
pp. 1-19 ◽  
Author(s):  
Xiaohui Jia ◽  
Minghui Jiang ◽  
Lei Shi
Keyword(s):  
Steady State ◽  
Evolutionary Game ◽  
Industrial Cluster ◽  
Industrial Clusters ◽  
Government Support ◽  
Correlated Equilibrium ◽  
Game Model ◽  
Cooperative Innovation ◽  
The Cost ◽  
The Impact

From the perspective of the interactive cooperation among subjects, this paper portrays the process of cooperative innovation in industrial cluster, in order to capture the correlated equilibrium relationship among them. Through the utilization of two key tools, evolutionary stable strategy and replicator dynamics equations, this paper considers the cost and gains of cooperative innovation and the amount of government support as well as other factors to build and analyze a classic evolutionary game model. On this basis, the subject’s own adaptability is introduced, which is regarded as the system noise in the stochastic evolutionary game model so as to analyze the impact of adaptability on the game strategy selection. The results show that, in the first place, without considering subjects’ adaptability, their cooperation in industrial clusters depends on the cost and gains of innovative cooperation, the amount of government support, and some conditions that can promote cooperation, namely, game steady state. In the second place after the introduction of subjects’ adaptability, it will affect both game theory selection process and time, which means that the process becomes more complex, presents the nonlinear characteristics, and helps them to make faster decisions in their favor, but the final steady state remains unchanged.

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