Because of their role in mediating life‐history trade‐offs, hormones are expected to be strongly associated with components of fitness; however, few studies have examined how natural selection acts on hormonal variation in the wild. In a songbird, the dark‐eyed junco (Junco hyemalis), field experiments have shown that exogenous testosterone alters individuals resolution of the survival‐reproduction trade‐off, enhancing reproduction at the expense of survival. Here we used standardized injections of gonadotropin‐releasing hormone (GnRH) to assay variation in the testosterone production of males. Using measurements of annual survival and reproduction, we found evidence of strong natural selection acting on GnRH‐induced increases in testosterone. Opposite to what would be predicted from the survival‐reproduction trade‐off, patterns of selection via survival and reproduction were remarkably similar. Males with GnRH‐induced testosterone production levels that were slightly above ...
Symbiotic associations with microorganisms are ubiquitously found in a variety of insects, which are rated among the important factors underpinning their adaptation, diversity, and prosperity (1⇓-3). Many bacterial symbionts are indispensable for growth, survival, and reproduction of their insect hosts via, for example, provisioning of essential nutrients like amino acids and vitamins, where the host and the symbiont are integrated into an almost inseparable biological entity (4, 5). In such obligate symbiotic associations, the symbiont genomes tend to exhibit conspicuous structural degeneration, massive gene losses, and drastic size reduction, which are attributable to relaxed natural selection acting on many symbiont genes no longer necessary for the permanent intrahost lifestyle, and also to accumulation of deleterious mutations driven by attenuated natural selection acting on the symbiont genomes due to strong population bottlenecks and restricted horizontal gene acquisitions associated ...
TY - JOUR. T1 - Population differentiation as an indicator of recent positive selection in humans. T2 - An empirical evaluation. AU - Xue, Yali. AU - Zhang, Xuelong. AU - Huang, Ni. AU - Daly, Allan. AU - Gillson, Christopher J.. AU - MacArthur, Daniel G.. AU - Yngvadottir, Bryndis. AU - Nica, Alexandra C.. AU - Woodwark, Cara. AU - Chen, Yuan. AU - Conrad, Donald F.. AU - Ayub, Qasim. AU - Mehdi, S. Qasim. AU - Li, Pu. AU - Tyler-Smith, Chris. PY - 2009/11. Y1 - 2009/11. N2 - We have evaluated the extent to which SNPs identified by genomewide surveys as showing unusually high levels of population differentiation in humans have experienced recent positive selection, starting from a set of 32 nonsynonymous SNPs in 27 genes highlighted by the HapMap1 project. These SNPs were genotyped again in the HapMap samples and in the Human Genome Diversity Project-Centre dEtude du Polymorphisme Humain (HGDP-CEPH) panel of 52 populations representing worldwide diversity; extended haplotype homozygosity was ...
Weak selection in evolutionary biology is when individuals with different phenotypes possess similar fitness, i.e. one phenotype is weakly preferred over the other. Weak selection, therefore, is an evolutionary theory to explain the maintenance of multiple phenotypes in a stable population [1]. Weak selection can only be used to explain the maintenance of mutations in a Moran process [1]. A Moran process in one which birth and death are paired events, and therefore population size remains constant. If the population size was increasing, both wild type and mutant phenotypes can proliferate and the weak selection for one phenotype results in no particular selection for either. Hence weak selection requires a finite population to operate. Otherwise there would be no expectation of fixation and hence no selection. The result of weak selection is two phenotypes with similar fixation probabilities. Weak selection works to elongate fixation time for two competing alleles. Consequently, weak selection ...
The distribution of variation in a quantitative trait and its underlying distribution of genotypic diversity can both be shaped by stabilizing and directional selection. Understanding either distribution is important, because it determines a populations response to natural selection. Unfortunately, existing theory makes conflicting predictions about how selection shapes these distributions, and very little pertinent experimental evidence exists. Here we study a simple genetic system, an evolving RNA enzyme (ribozyme) in which a combination of high throughput genotyping and measurement of a biochemical phenotype allow us to address this question. We show that directional selection, compared to stabilizing selection, increases the genotypic diversity of an evolving ribozyme population. In contrast, it leaves the variance in the phenotypic trait unchanged. ...
TY - JOUR. T1 - Methods of increasing short term response to full-sib family recurrent selection in small populations. AU - Mackay, I. J.. AU - Caligari, P. D.S.. PY - 2000. Y1 - 2000. N2 - Accelerated recurrent selection (ARS), in which selection is carried out on the predicted value of the progeny rather than on the observed performance of the parents, has been proposed as a method of increasing response to selection and of reducing cycle time. ARS schemes based on test cross evaluation of full-sib families have been compared by stochastic computer simulation. The difference in genetic and economic time scales is emphasised, with the economic long term (21 years) being only 21 or fewer cycles of selection. ARS schemes are shown frequently to offer improvements over standard recurrent selection methods under these circumstances, since they allow more cycles of selection in a given time frame. Schemes with very low effective population sizes often give the greatest response to selection over the ...
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TY - JOUR. T1 - The origin of mutants under selection. T2 - How natural selection mimics mutagenesis (adaptive mutation). AU - Maisnier-Patin, Sophie. AU - Roth, John R.. PY - 2015/7/1. Y1 - 2015/7/1. N2 - Selection detects mutants but does not cause mutations. Contrary to this dictum, Cairns and Foster plated a leaky lac mutant of Escherichia coli on lactose medium and saw revertant (Lac+) colonies accumulate with time above a nongrowing lawn. This result suggested that bacteria might mutagenize their own genome when growth is blocked. However, this conclusion is suspect in the light of recent evidence that revertant colonies are initiated by preexisting cells with multiple copies the conjugative F′lac plasmid, which carries the lac mutation. Some plated cells have multiple copies of the simple F′lac plasmid. This provides sufficient LacZ activity to support plasmid replication but not cell division. In nongrowing cells, repeated plasmid replication increases the likelihood of a reversion ...
We discussed a few possibilities that would fit nicely with my planned thesis and settled on an idea which Rowan had had in mind for a few years: a meta-analysis of genetic selection coefficients in natural populations. Biologists have been measuring phenotypic selection gradients and differentials since the 1980s, when Lande and Arnold developed the multiple regression methods used to quantify phenotypic selection. Influential meta-analyses of these data (e.g., Kingsolver et al. 2001, Rieseberg et al. 2002, Hereford et al. 2004, Siepielski et al. 2001 and 2013, and others) have told us a lot about how natural selection operates at the phenotypic level. At the genotypic level, however, fundamental questions remain: how strong is natural selection on allelic variation? How does selection vary through time and space? How are selection coefficients distributed? That these questions remain largely unanswered is partially due to technological limitations: biologists couldnt directly measure ...
Antagonistic selection-where alleles at a locus have opposing effects on male and female fitness ("sexual antagonism"), or between components of fitness ("antagonistic pleiotropy")-might play an important role in maintaining population genetic variation, and in driving phylogenetic and genomic patterns of sexual dimorphism and life-history evolution. While prior theory has thoroughly characterized the conditions necessary for antagonistic balancing selection to operate, we currently know little about the evolutionary interactions between antagonistic selection, recurrent mutation, and genetic drift, which should collectively shape empirical patterns of genetic variation. To fill this void, we developed and analyzed a series of population genetic models that simultaneously incorporate these processes. Our models identify two general properties of antagonistically selected loci. First, antagonistic selection inflates heterozygosity and fitness variance across a broad parameter range-a result that ...
TY - CHAP. T1 - Identifying Selection Signatures in Mammalian Genes Through the Analysis of Patterns of Gene Expression. AU - Urrutia, Araxi. AU - Hurst, Laurence. PY - 2005. Y1 - 2005. M3 - Chapter. BT - SAGE: Current Technologies and Applications. A2 - Wang, SM. PB - Horizon Bioscience. ER - ...
The spectacular diversity in sexually selected traits among animal taxa has inspired the hypothesis that divergent sexual selection can drive speciation. Unfortunately, speciation biologists often consider sexual selection in isolation from natural selection, even though sexually selected traits evolve in an ecological context: both preferences and traits are often subject to natural selection. Conversely, while behavioural ecologists may address ecological effects on sexual communication, they rarely measure the consequences for population divergence. Herein, we review the empirical literature addressing the mechanisms by which natural selection and sexual selection can interact during speciation. We find that convincing evidence for any of these scenarios is thin. However, the available data strongly support various diversifying effects that emerge from interactions between sexual selection and environmental heterogeneity. We suggest that evaluating the evolutionary consequences of these ...
Cyclical selection that does not result in gene fixation may maintain a parent-offspring (P-O) correlation in fitness that is, most of the time, not far below one-half. This tends to happen when the following conditions are fulfilled: (i) slow cycling in allele frequencies occurs at many loci independently; (ii) most alleles make only small differences to fitness; (iii) dominance in allelic fitness contribution is rare and overdominance rarer still. In contrast, drastic cyclical selection (dependent on large fitness differences without overdominance), because direction reverses so frequently, may give P- 0 correlations in fitness th a t are near zero or even negative. Also, if much fitness variance is maintained by heterozygote advantage, or is caused environmentally, the correlation is reduced in proportion to the ratio of relevant standard deviations. P - 0 correlation in fitness that is almost permanently positive may help to explain mate choice in sexually promiscuous species. The most ...
In the models presented above, a locus segregates for alleles with higher than average fitness for one sex and lower than average fitness for the other. Therefore, these are models of intralocus sexual conflict, also known as sexual antagonism or intersexual ontogenetic conflict (Rice & Chippindale 2001). Consistent with previous work, we find that such intralocus conflict can maintain genetic variation, especially when the sexual antagonism is strong (Prout 2000). Our two models are qualitatively similar except that selection is attenuated in the madumnal effect model because half of the gene pool (padumnal alleles) is shielded from selection. This is similar to the dilution of the force of selection for genes with maternal effects, the so-called relaxed constraint (Barker et al. 2005).. Our madumnal effect model applies not only to organisms with dominant haploid life cycles but also to diploid organisms with imprinted gene expression. Though the site of gene expression differs for an ...
Under the Sawyer-Hartl Poisson random field model, comparisons of the configurations of functional categories of DNA mutations can have considerable power to detect even very weak directional selection on classes of DNA mutations. These findings cannot be generalized beyond evolution under the parameter ranges considered and under the Sawyer-Hartl assumptions of stationarity, free recombination, and independent fitness effects of all mutations. Given these assumptions, configuration comparisons that include information from both frequency distributions of polymorphic mutations and numbers of fixed differences confer the greatest power to detect the fitness effects of mutations. The Mann-Whitney U-test, which is sensitive to differences in the locations of distributions, is a more powerful statistical approach to detect uniform selection coefficients than contingency tests of homogeneity. Accumulating DNA variation data for a large number of mutations with similar fitness effects is critical to ...
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Posted on 09/27/2006 9:56:09 AM PDT by SirLinksalot. Why Darwinism is doomed -------------------------------------------------------------------------------- Posted: September 27, 2006 1:00 a.m. Eastern By Jonathan Wells, Ph.D. -------------------------------------------------------------------------------- © 2006 Harvard evolutionary biologist Stephen Jay Gould wrote in 1977: Biology took away our status as paragons created in the image of God. Darwinism teaches that we are accidental byproducts of purposeless natural processes that had no need for God, and this anti-religious dogma enjoys a taxpayer-funded monopoly in Americas public schools and universities. Teachers who dare to question it openly have in many cases lost their jobs. The issue here is not evolution a broad term that can mean simply change within existing species (which no one doubts). The issue is Darwinism which claims that all living things are descended from a common ancestor, modified by natural selection acting on ...
Define artificial selection. artificial selection synonyms, artificial selection pronunciation, artificial selection translation, English dictionary definition of artificial selection. n. Human intervention in animal or plant reproduction or survival to allow only individuals with desirable traits to reproduce. n. a process in the breeding...
Phylogenetic codon models are often used to characterize the selective regimes acting on protein-coding sequences. Recent methodological developments have led to models explicitly accounting for the interplay between mutation and selection, by modeling the amino acid fitness landscape along the sequence. However, thus far, most of these models have assumed that the fitness landscape is constant over time. Fluctuations of the fitness landscape may often be random or depend on complex and unknown factors. However, some organisms may be subject to systematic changes in selective pressure, resulting in reproducible molecular adaptations across independent lineages subject to similar conditions. Here, we introduce a codon-based differential selection model, which aims to detect and quantify the fine-grained consistent patterns of adaptation at the protein-coding level, as a function of external conditions experienced by the organism under investigation. The model parameterizes the global mutational pressure,
Genome-wide scanning for signals of recent positive selection is essential for a comprehensive and systematic understanding of human adaptation. Here, we present a genomic survey of recent local selective sweeps, especially aimed at those nearly or recently completed. A novel approach was developed …
Shermer wrote the foreword to Prothero s book, calling it the best book ever written on the subject. In fact, Don s visual presentation of the fossil and genetic evidence for evolution is so unmistakably powerful that I venture to say that no one could read this book and still deny the reality of evolution. Of course, evolution can mean many things, most of which nobody would deny even without Prothero s book. For example, evolution can mean simply change over time, or minor changes in existing species ( microevolution ), neither of which any sane person doubts. Both Shermer and Prothero, however, make it clear that by evolution they mean Darwin s theory that all living things are descended from a common ancestor, modified principally by natural selection acting on unguided variations ( macroevolution ).. The modern version of the theory asserts that new variations originate in genetic mutations. Some of the most dramatic mutations occur in Hox genes, which can determine which appendages develop ...
Like drivers at a carwash, coral reef fish queue at cleaning stations to have parasites, slime, and broken scales nibbled away by smaller fish and by shrimps. These species interactions are interesting for their tropical ubiquity and the diversity of species that can be found as clients and cleaners. Although some cleaners are obligate professionals, others are dilettantes and adopt this life-style intermittently.. Floeter et al. have compiled data from around the tropics to tease out the selection pressures acting on these interactions. The basic emerging relationship is that, owing to abundance, the more common, planktivorous, and gregarious species take up most of the cleaners time. Client size doesnt seem to be very important, nor does professionalism, when it comes to dealing with carnivores that might eat the fish or shrimp that is cleaning them. Hence, this study adds to a growing body of evidence suggesting a central role for abundance in structuring species interactions. Guimarães et ...
Which Evolution do you believe in when you say, "Evolution is so powerful"? Darwin didnt have a mechanism; there was no knowledge of DNA polymerase and Meiotic cell division in those days. He was more concerned with proving the superiority of the Anglo Saxon race. Hence the subtitle of his 1st book, "…and the preservation of favored races", and the thrust of his 2nd book, "The descent of man". "Natural selection acting on random mutations" doesnt work as a creative force, either. Its a reducing force, if anything. We have never seen that mechanism producing a new species. Remember, Darwins book wasnt called "How species change over time"; it was "how new species originate". All we observe is the reshuffling of existing genetic material (reshuffling of the deck of cards), or laboratory recombinations that produce freaks (fruit flies with useless wings or legs growing out of their heads), or sterile polyploidy in the plant kingdom. Currently, there is a crisis with the standard neo-Darwin ...
However, principles of natural selection may also hold key to thwarting emergence of drug resistance. According to researchers at Moffitt Cancer Center, cancer is subject to the evolutionary processes laid out by Charles Darwin in his concept of natural selection. Natural selection was the process identified by Darwin by which nature selects certain physical attributes, or phenotypes, to pass on to offspring to better "fit" the organism to the environment.. As applied to cancer, natural selection, a key principle of modern biology, suggests that malignancies in distinct "microhabitats" promote the evolution of resistance to therapies. However, these same evolutionary principles of natural selection can be applied to successfully manage cancer, say Moffitt researchers who published an opinion piece in a recent issue of Nature Reviews Cancer.. "Understanding cancer as a disease starts with identifying crucial environmental forces and corresponding adaptive cellular strategies," said Robert A. ...
Free-living bacteria are usually thought to have large effective population sizes, and so tiny selective differences can drive their evolution. However, because recombination is infrequent, "background selection" against slightly deleterious alleles should reduce the effective population size (N e) by orders of magnitude. For example, for a well-mixed population with 10 12 individuals and a typical level of homologous recombination (r/m= 3, i.e., nucleotide changes due to recombination [r] occur at 3 times the mutation rate [m]), we predict that N e is,10 7. An argument for high N e values for bacteria has been the high genetic diversity within many bacterial "species," but this diversity may be due to population structure: diversity across subpopulations can be far higher than diversity within a subpopulation, which makes it difficult to estimate N e correctly. Given an estimate ofN e, standard population genetics models imply that selection should be sufficient to drive evolution if N e ×s is ...
TY - JOUR. T1 - Evolution of mitotic cell-lineages in multicellular organisms. AU - Fagerström, Torbjörn. AU - Briscoe, David A.. AU - Sunnucks, Paul. PY - 1998/3. Y1 - 1998/3. N2 - Adaptive evolution in multicellular organisms is generally assumed to occur through natural selection acting differentially among the phenotypes programmed by sexually-generated zygotic genotypes. Under this view, only genetic changes in the gamete-zygote-germline-gamete cycle are considered relevant to the evolutionary process. Yet asexuality - production of progeny through proliferation of mitotic cell-lineages - is found in over one half of all eukaryotic phyla, and is likely to contribute to adaptive changes, as suggested by recent evidence from both animals and plants. Adaptive changes in mitotic lineages can be reconciled with contemporary evolutionary thought by fully abandoning the weismannian concept of individuality.. AB - Adaptive evolution in multicellular organisms is generally assumed to occur through ...
The self-seeded landscape that runs above the High Line at the Rail Yards gives visitors a chance to see what the High Line looked like before it b...
Evolution, at the molecular level, is observableas nucleotide changes in the DNA and amino acid changes in proteins. Both polymorphism and evolutionary change between species can be explained by the two processes of natural selection and genetic drift. Two factors controlling the relative importance of neutral drift and natural selection:. 1. Population size. If the population is small then neutral drift dominates; whereas natural selection does if the population is large. 2. The selection coefficients of the different genotypes. If the selection coefficients are low then neutral drift dominates, otherwise natural selection is the more important.. In the evolution of modern species, there have been millions of molecular changes. Natural selection and neutral drift could logically have produced any proportions of the changes, but exactly what proportion is an open question among evolutionary biologists. Richard Dawkins offers his own view.. ...
For its outpost at the High Line, Bark is collaborating with Dicksons Farmstand Meats in Chelsea Market to source animals from local, small-scale ...
Traditional genome-wide scans for positive selection have mainly uncovered selective sweeps associated with monogenic traits. While selection on quantitative traits is much more common, very few signals have been detected because of their polygenic nature. We searched for positive selection signals underlying coronary artery disease (CAD) in worldwide populations, using novel approaches to quantify relationships between polygenic selection signals and CAD genetic risk. We identified new candidate adaptive loci that appear to have been directly modified by disease pressures given their significant associations with CAD genetic risk. These candidates were all uniquely and consistently associated with many different male and female reproductive traits suggesting selection may have also targeted these because of their direct effects on fitness. We found that CAD loci are significantly enriched for lifetime reproductive success relative to the rest of the human genome, with evidence that the ...
Traditional genome-wide scans for positive selection have mainly uncovered selective sweeps associated with monogenic traits. While selection on quantitative traits is much more common, very few signals have been detected because of their polygenic nature. We searched for positive selection signals underlying coronary artery disease (CAD) in worldwide populations, using novel approaches to quantify relationships between polygenic selection signals and CAD genetic risk. We identified new candidate adaptive loci that appear to have been directly modified by disease pressures given their significant associations with CAD genetic risk. These candidates were all uniquely and consistently associated with many different male and female reproductive traits suggesting selection may have also targeted these because of their direct effects on fitness. We found that CAD loci are significantly enriched for lifetime reproductive success relative to the rest of the human genome, with evidence that the ...
Calculating Nucleotide Sequence Polymorphism. This is the seventh of multiple postings I plan to write about detecting natural selection using molecular data (ie, DNA sequences). The first post contained a brief introduction and can be found here. The second post described the organization of the genome, and the third described the organization of genes. The fourth post described codon based models for detecting selection, and the fifth detailed how relative rates can be used to detect changes in selective pressure. The sixth post dealt with classical population methods for detecting selection using allele and genotype frequencies.. Much of the popular press surrounding recent publications that proclaim to detect natural selection does not adequately detail whether the researchers have identified purifying selection (selective constraint) or positive (aka Darwinian) selection. See here for a particularly poor article that confused the heck out of me (and I claim to understand genome analysis). ...
Introduction. The subject of this chapter is how natural selection acts on age-structured populations, in which age-specific patterns of survival probabilities and reproductive rates are the fundamental parameters describing the life history of a genotype. This is a large subject, and the chapter does not offer a comprehensive review. Instead, I will concentrate on some aspects on which I myself have worked. My interest in the subject was stimulated as a beginning postdoc in Dick Lewontins laboratory, over 30 years ago, when he and Tim Prout expressed some well-justified skepticism about the logical basis of the use of Fishers "Malthusian parameters" (Fisher 1930, Chapter 2) for modeling selection in populations with overlapping generations (Charlesworth 1970). I have contributed, somewhat fitfully, to this subject during much of my subsequent career.. The fundamental problem is how to describe selection in the context of a population divided into different age groups. This provides the basis ...
He wraps up the chapter with a discussion of what he calls "deflector beliefs", those beliefs that result in not being able to arrive at a separate specific belief. At a very simple level the concept is one of presuppositions; the beliefs you bring into a situation will influence the beliefs you form about a situation. This is just as much an argument against the argument from design as anything else. If my children are taught evolution through natural selection at a young age and do not receive religious teachings, the argument from design will have no foothold. The argument from design will be, quite simply, a non-starter. They wont be employing the same propositional attitudes as a theist. Plantinga offers that a hypothetical neutral observer would likely be pre-disposed to conclude design, but doesnt thoroughly argue that point. I dont think it can be well defended in any case ...
The general conclusion may be stated in a simple manner, but I believe that the resulting implications for evolutionary theory are both profound and curiously underappreciated: If many features that operate as adaptations under present regimes of natural selection were exapted from ancestral features with nonadaptive origins-and were not built as adaptations for their current use (or exapted from ancestral features with adaptive origins for different functions)-then we cannot explain all the pathways of evolutionary change under functionalist mechanics of the theory of natural selection. Instead, we must allow that many important (and currently adaptive) traits originated for nonadaptive reasons that cannot be attributed to the direct action of natural selection at all and, moreover, cannot be inferred from the exaptive utility of the trait in living species. Because the subject of evolutionary biology must engage many critical questions about the origins of features, and cannot be confined to ...
The general conclusion may be stated in a simple manner, but I believe that the resulting implications for evolutionary theory are both profound and curiously underappreciated: If many features that operate as adaptations under present regimes of natural selection were exapted from ancestral features with nonadaptive origins-and were not built as adaptations for their current use (or exapted from ancestral features with adaptive origins for different functions)-then we cannot explain all the pathways of evolutionary change under functionalist mechanics of the theory of natural selection. Instead, we must allow that many important (and currently adaptive) traits originated for nonadaptive reasons that cannot be attributed to the direct action of natural selection at all and, moreover, cannot be inferred from the exaptive utility of the trait in living species. Because the subject of evolutionary biology must engage many critical questions about the origins of features, and cannot be confined to ...
Humans can more easily tolerate tumours in large or paired organs than in small, critical ones. This could be why the latter have evolved more cancer-fighting mechanisms.
In these 28 DR-I blocks, the average diversity was 0.00013 (ranging from 0.00003 to 0.00020) within japonica and 0.00017 (ranging from 0.00011 to 0.00025) within indica (Table 2). However, the average divergence between these two groups was 0.0034, which was 11- to 101-fold higher (~27-fold on average) than the diversity within each group (Table 2), suggesting significant differentiation between indica and japonica in these regions. The average diversity is ~15-fold lower within japonica and ~16-fold lower within indica than their corresponding genome-wide diversity, suggesting strong selection with selective sweep on these regions. On the other hand, in these blocks, significantly positive correlations were displayed either in the diversity within indica vs. japonica, or D ind-jap vs. π jap or π ind , or D jap-wild and D ind-wild (Additional file 1: Figure S3). This was consistent with the possibility that japonica and indica may have undergone strong artificial selection from different ...
Having recklessly abandoned one long-held prejudice (that eukaryotic nuclear genomes are necessarily more "advanced" than eubacterial genomes), we were emboldened to discard another: that most or all of the sometimes huge amount of DNA which eukaryotes carry around with them arose though and is maintained by natural selection operating though phenotype, either at the level of the individual or the population. The suggestion that much of this excess DNA is "junk" (the product of no form of natural selection at all) had of course been made before. But C. Sapienza and I suggested, as did L. Orgel and F. Crick, that natural selection of a hitherto little-appreciated type ("nonphenotypic" or "intragenomic" selection) perforce must operate within genomes to produce and maintain DNAs which, by virtue of their sequences (or the products of those sequences) alone, are more likely to be perpetuated within genomes, regardless of their effect on phenotype. We described such DNAs as "selfish" or "parasitic," ...
Natural selection can result in new adaptations or in the elimination of bad traits. The former is "positive" selection, the latter is "negative" and is always occurring no matter what. Positive selection does happen but is not easy to test, since natural selection occurs via differential reproductive success, but "survival of the luckiest" alleles via genetic drift can look exactly the same by increasing and decreasing allele frequencies just by chance. The difference between the two is that, in a selection scenario, the trait thats evolving is causing the differential reproduction (whether enhancing or inhibiting, even if ever so slightly affecting it slowly over time), but in a genetic drift scenario the trait is randomly "drifting" to lower or higher frequencies merely due to chance (unlinked to the trait in question) effects on differential reproduction and chance passing of one allele or the other to offspring. Like selection, drift can completely fix or completely eliminate traits. ...
Natural selection can result in new adaptations or in the elimination of bad traits. The former is "positive" selection, the latter is "negative" and is always occurring no matter what. Positive selection does happen but is not easy to test, since natural selection occurs via differential reproductive success, but "survival of the luckiest" alleles via genetic drift can look exactly the same by increasing and decreasing allele frequencies just by chance. The difference between the two is that, in a selection scenario, the trait thats evolving is causing the differential reproduction (whether enhancing or inhibiting, even if ever so slightly affecting it slowly over time), but in a genetic drift scenario the trait is randomly "drifting" to lower or higher frequencies merely due to chance (unlinked to the trait in question) effects on differential reproduction and chance passing of one allele or the other to offspring. Like selection, drift can completely fix or completely eliminate traits. ...
You didnt have me down as anti-evolution, but I did have you down as particularly precious… The simple point about the Theory of evolution is that its still not proven. As much as people mighnt like it, there isnt firm proof.. "Antibiotic resistance evolves naturally via natural selection acting upon random mutation". Just because the word evolves is used in that sentence doesnt mean theres evolution in play. Evolves is simply used in place of occurs there.. "but it can also be engineered by applying an evolutionary stress on a population.". And an evolutionary stress doesnt imply evolution either, simply that something is introduced which will force natural selection to occur. Either way, antibiotic resistance isnt a result of evolution nor a demonstration of it. Its down to natural selection - hence the point that at no point in the process do the bacteria ever become more complex. Genetic material is not produced and at the end theyre still plain old bacteria.. Id be happy if ...
Natural selection drives populations toward higher fitness, but second-order selection for adaptability and mutational robustness can also influence evolution. In many microbial systems, diminishing-returns epistasis contributes to a tendency for more-fit genotypes to be less adaptable, but no analogous patterns for robustness are known. To understand how robustness varies across genotypes, we measure the fitness effects of hundreds of individual insertion mutations in a panel of yeast strains. We find that more-fit strains are less robust: They have distributions of fitness effects with lower mean and higher variance. These differences arise because many mutations have more strongly deleterious effects in faster-growing strains. This negative correlation between fitness and robustness implies that second-order selection for robustness will tend to conflict with first-order selection for fitness. ...
Natural selection can result in new adaptations or in the elimination of bad traits. The former is "positive" selection, the latter is "negative" and is always occurring no matter what. Positive selection does happen but is not easy to test, since natural selection occurs via differential reproductive success, but "survival of the luckiest" alleles via genetic drift can look exactly the same by increasing and decreasing allele frequencies just by chance. The difference between the two is that, in a selection scenario, the trait thats evolving is causing the differential reproduction (whether enhancing or inhibiting, even if ever so slightly affecting it slowly over time), but in a genetic drift scenario the trait is randomly "drifting" to lower or higher frequencies merely due to chance (unlinked to the trait in question) effects on differential reproduction and chance passing of one allele or the other to offspring. Like selection, drift can completely fix or completely eliminate traits. ...
A system (and method) assists consideration of selection that recommends selection candidates to a considerer who is considering selection in a certain field in order to assist determination of selection with which the considerer is satisfied. A question concerning the field is sent to a considerer and answer data is received from the considerer by the system. A degree-of-significance of each evaluation item in the field is estimated from the answer data. A degree-of-recommendation representing to which degree each selection candidate can be recommended to the considerer is calculated from evaluation data for each evaluation item with respect to each piece of selection candidate data in the field and the degree-of-significance of the considerer with respect to each evaluation item. Then, degrees of recommendation of selection candidate data in the field are presented to the considerer without change or after processing the data.
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Obligate self-mediated positive selection in the maturation, lineage determination, and homeostasis of peripheral B cells, coupled with parallels in T lymphocyte development and homeostasis, compels consideration of the underlying biological rationale. One possibility is that sufficient repertoire diversity is ensured through positive selection and continuous intraclonal competition. The reasoning for this argument is that if intraclonal competition for self-epitopes determines fitness, then overlapping specificities will compete but nonoverlapping specificities will not, thus favoring diversity. Whether diversity per se is the ultimate end point of positive selection might be questioned from the standpoint that the random genetic processes used for receptor generation will likely insure diversity given adequate pool size and turnover rates. Furthermore, mice bearing a single VH gene were able to generate high-affinity Abs to several T-dependent protein Ags using CDR3 variability and somatic ...
The origin and persistence of adaptive polymorphisms is a puzzling question for evolutionary biologists [1-4]. Adaptive polymorphisms can be defined as several coexisting phenotypes within a population, which correspond to fitness peaks in an adaptive landscape. Such landscapes may comprise one or many dimensions, depending on the complexity of the adaptive trait. Understanding the evolution of adaptive polymorphism in a complex trait is especially challenging, because natural selection can act on different features of the trait and thus on multiple dimensions of the fitness landscape. Therefore, the exploration of new adaptive peaks in such a landscape usually requires coordinated changes in multiple axes to cross fitness valleys [5]. Gradual changes alone are thought to be generally unable to bridge such fitness valleys [6]. Mechanisms such as epistasis (i.e. when several neutral or deleterious mutations produce fitness benefits when they co-occur) [7] or large size mutation followed by ...
According to evolutionary theories of mind, that we have evolved under certain selective pressures not only causally explains our mental functioning, but in fact is essential to that very functioning. Thus, if an exact duplicate of one of us came into existence at random, with no selection, it would not have a mind. The reason is that components of minds have to have proper functions, and proper functions in us are to be analyzed through natural selection.. Of course, there could be critters whose proper function is to be analyzed in terms of artificial selection, or even in terms of design by an agent. But as it happens, we are not critters like that, says the evolutionary theorist of mind. Nonetheless, it is important that the account of proper function be sufficiently flexible that artificial selection would also be able to give rise to proper function (after all, how would one draw the line between artificial and natural selection, when artificial selectors-say, human breeders-are apt ...
On the standard Darwinian view of natural selection, the mechanism of natural selection operates on individual organisms. Because there is heritable variation within a population of conspecifics with respect to traits that imbue those organisms with differing levels of fitness, natural selection can increase the proportion of organisms with traits that promote fitness. Many biologists and philosophers of biology have recognized that the substrate-neutrality of the conditions for natural selection imply in principle that it can act on a large variety of entities in the biological hierarchy, stretching from the very small (e.g., single base pairs) through to the very large (e.g., clades). And there are a variety of proposals for what is required to be an entity that selection can act on-what is required to be an evolutionary individual or agent (e.g., Bouchard 2008, and see Clarke 2010). But as a matter of fact the bulk of discussion that moves beyond the standard Darwinian view has focused on two ...
Looking for intermediate frequency? Find out information about intermediate frequency. The frequency produced by combining the received signal with that of the local oscillator in a superheterodyne receiver. Abbreviated i-f. In superheterodyne... Explanation of intermediate frequency
Abstract: Arguments about the evolutionary modification of genetic dominance have a long history in genetics, dating back more than 100 years. Mathematical investigations have shown that modifiers of the level of dominance at the locus of interest can spread at a reasonable rate only if heterozygotes at that locus are common. One hitherto neglected scenario is that of sexually antagonistic selection, which not only is ubiquitous in sexual species but also can generate stable high frequencies of heterozygotes that would appear to facilitate the spread of such modifiers. Here we present a mathematical model that shows that sexually specific dominance modification is a potential outcome of sexually antagonistic selection. Our model predicts that loci with higher levels of sexual conflict should exhibit greater differentiation between males and females in levels of dominance and that the strength of antagonistic selection experienced by one sex should be proportional to the level of dominance ...
In all these cases, change is a random, chance occurrence, whereas natural selection is a law which always operates on such changes. In spite of the terms often used to express evolutionary change ("Flowers have colors in order to attract bees."), it is not teleological (goal-oriented). "Colored flowers attract bees and so survive better.". Natural selection acts on changes brought about by the other mechanisms cited. In addition, sex is a source of gene mixing, as will be discussed in a later chapter. But the oddest source of change is shuffling of the genetic material when antibodies are created in our bodies. More on that later, too.. Like quantum mechanics, evolution injects the theme of randomness into our understanding of the workings of the universe, but not at all on the same scale.. Species. The notion of species has been much discussed in the history of biology before arriving at the current definition of a species as "groups of interbreeding natural populations, which are ...
gamila, let me try to walk you through this. Evolution is based on two principles: descent with modification and natural selection. Descent with modification just means that new muations are inherited from parent to offspring. Darwin didnt know the source of modifications, but modern genetics understands it well. New mutations in DNA happen all the time. Errors during the replication of DNA when a cell divides, radiation from a variety of natural and man-made sources, various chemicals in the environment - these can all cause mutations. When they happen in germ cells (sperm and eggs in sexually reproducing organisms, or anywhere in unicellular organisms that reproduce by simply dividing), these new changes are inherited. Now, natural selection. This seems to be where you are having trouble. You say that natural selection only acts on traits that are already present. You are absolutely right. But you must admit that there is variation within species. No two people are the same. Dogs are a good ...
According to the neutral theory of evolution most mutations are expected to be neutral, nearly neutral, or deleterious. It is the class of nearly neutral and deleterious mutations that may, in fact, predominantly drive the evolution and structure of the genome. The removal of deleterious mutations by purifying selection can affect genetic variation at linked neutral sites by a process called background selection. There is renewed interested in understanding background selection across diverse organisms, and comparing diversity between the sex chromosomes and the autosomes to distinguish its effects from other evolutionary forces, such as demography and positive selection. Recent advances include new theoretical approaches to more comprehensively model the complexity of background selection in a coalescent framework. These models are especially powerful when combined with recent developments resulting in dramatically increased sample sizes, improved identification of rare variants, and the ...
A weird happening has occurred in the case of a lansquenet named Daniel Burghammer, of the squadron of Captain Burkhard Laymann Zu Liebenau, of the honorable Madrucci Regiment in Piadena, in Italy. When the same was on the point of going to bed one night he complained to his wife, to whom he had been married by the Church seven years ago, that he had great pains in his belly and felt something stirring therein. An hour thereafter he gave birth to a child, a girl. When his wife was made aware of this, she notified the occurrence at once. Thereupon he was examined and questioned. He confessed on the spot that he was half man and half woman and that for more than seven years he had served as a soldier in Hungary and the Netherlands . When he was born he was christened as a boy and given in baptism the name of Daniel . He also stated that while in the Netherlands he only slept once with a Spaniard, and he became pregnant therefrom. This, however, he kept a secret unto himself and also from his wife, ...
Think about the factors that will influence the evolution of humans in the future. Name one factor that would exert influence through natural selection and one factor that would exert influence through artificial selection ...
This is partly tradition - a mark of academic independence in evolutionary biology seems to be choosing your own research system (organism+field site+questions of interest), but it might also partly arise from the nature of the field. The process of evolution is intrinsically tied more to variation than to shared properties - natural selection acts on differences, not similarities. So maybe choosing to work on different systems just looks like the sensible thing to do ...
Since both orthologous and paralogous genes can be included in the same gene cluster, positive selection detected in a cluster can be a result of various processes: adaptation of a species to optimise the process of infection, escape host immune response, adaptation to a different environmental niches (e.g., milk in S. thermophilus, or dental flora in S. mutans), and functional diversification of members of multi-gene families. Indeed, the 136 clusters identified as having evolved under positive selection were connected to a wide variety of functions (see Additional file 1), with only 10% having no ascribable function. Interestingly, 7% of the clusters were comprised of genes known to be essential to S. pneumoniae (see Additional file 1), i.e. those where experimental disruption was shown to be lethal [23], indicating that even essential genes can be subject to rapid evolution by natural selection. A substantial fraction of the clusters, (29%) had either a known, or hypothesised, connection to ...
If we assume that selection acts on the amino acid sequence (the protein encoded by the gene) then the synonymous substitutions should be selectively neutral. This is not necessarily true, and is a legitimate concern in some instances, but we will ignore it here. We can count the number of synonymous and non-synonymous substitutions in a gene if we have a copy from two different species (for example, human and mouse). To standardize for differences in the number of synonymous and non-synonymous sites (there are more than twice as many non-synonymous sites in a coding sequence because, for the most part, only the third codon position is redundant), we calculate the number of synonymous differences per synonymous sites (kS or dS) and the number of non-synonymous differences per non-synonymous sites (kA or dN). The two types of statistics (dS and dN versus kS and kA) differ in how synonymous and non-synonymous sites are calculated -- for this discussion, I will be using dS and dN.. ...
Author Summary Species differ genetically, and the way in which they vary is informative about the workings of natural selection: the proportion of the genome subject to selection, the degree to which selection has conserved function versus favoring novel forms, and the location of genes responsible for evolutionarily important adaptations that explain differences in biology between the species. Individuals also vary within species, and that variation provides a snapshot of the process of evolution, a snapshot that is useful for contrasting recent versus long-term evolution and for understanding the role of mutations that are destined to be lost from the population. However, existing methods tend to use only one of these sources of information. We have developed a tool to analyze variation within and between species jointly that is able to detect fine-scale differences in the action of natural selection within genes. By applying this method to 100 genes surveyed in three species of fruit fly, we show
View Notes - TENTATIVE FAIR 2 from PSY 1 at UCSB. TENTATIVE FAIR-GAME SHEET - FINAL EXAM Natural Selection and Motivation Natural selection Those with better genes will reproduce more because they
Strong natural pain killers that are better than drugs. The individual continuously suffers from pains inside the muscle groups, in the joints, in the head.
Scientists who do experimental genetics employ artificial selection experiments that permit the survival of organisms with user-defined phenotypes. Artificial selection is widely used in the field of microbial genetics, especially molecular cloning.. DNA recombination has been used to create gene replacements, deletions, insertions, inversions. Gene cloning and gene/protein tagging is also common. For gene replacements or deletions, usually a cassette encoding a drug-resistance gene is made by PCR.. Molecular cloning is a set of experimental methods in molecular biology that are used to assemble recombinant DNA molecules and to direct their replication within host organisms. The use of the word cloning refers to the fact that the method involves the replication of a single DNA molecule starting from a single living cell to generate a large population of cells containing identical DNA molecules. Molecular cloning generally uses DNA sequences from two different organisms: the species that is the ...
Does natural selection act primarily on individual organisms, on groups, on genes, or on whole species? The question of levels of selection - on which biologists and philosophers have long disagreed - is central to evolutionary theory and to the philosophy of biology. Samir Okashas comprehensive analysis gives a clear account of the philosophical issues at stake in the current debate.
Levels of genetic differentiation between populations can be highly variable across the genome, with divergent selection contributing to such heterogeneous genomic divergence. For example, loci under divergent selection and those tightly physically linked to them may exhibit stronger differentiation than neutral regions with weak or no linkage to such loci. Divergent selection can also increase genome-wide neutral differentiation by reducing gene flow (e.g. by causing ecological speciation), thus promoting divergence via the stochastic effects of genetic drift. These consequences of divergent selection are being reported in recently accumulating studies that identify: (i) outlier loci with higher levels of divergence than expected under neutrality, and (ii) a positive association between the degree of adaptive phenotypic divergence and levels of molecular genetic differentiation across population pairs [isolation by adaptation (IBA)]. The latter pattern arises because as adaptive divergence ...
Phenotypic differences between the sexes evolve largely because selection favours a different complement of traits in either sex. Theory suggests that, despite its frequency, sexual dimorphism should be generally constrained from evolving because the sexes share much of their genome. While selection can lead to adaptation in one sex, correlated responses to selection can be maladaptive in the other. In this thesis I use Drosophila to examine the extent to which the shared genome constrains the evolution of sexual dimorphism and whether the sex chromosomes might play a special role in resolving intralocus sexual conflict.. Gene expression data shows that intersexual genetic correlations are generally high, suggesting that genes often affect both sexes. The intersexual genetic correlation is negatively associated with sex-bias in expression in D. melanogaster, and the rate of change in sex-bias between D. melanogaster and six closely related species, showing that a sex-specific genetic ...
Gratuit Sexual selection Evolution Sexual selection is a "special case" of natural selection. Sexual selection acts on an organisms ability to obtain (often by any means necessary!) or successfully ... Mitsubishi Motors OUTLANDER PHEV MISLI NAPREDNO, VOZI NAPREDNO Predstavljamo Vam revolucionarni Outlander PHEV istodobno uzbudljiv i prijazan prema okoliu. Spoj inovativne tehnologije iz ... Using VB graphics commands in VBA Eng Tips Forums I am attempting to use the graphics commands methods described in Rod Stephens Visual Basic Graphics Programming in VBA with Excel. Im hoping to be able to add Evolution (2001) IMDb With David Duchovny, Julianne Moore, Orlando Jones, Seann William Scott. A fire fighting cadet, two college professors, and a geeky but sexy government scientist work ... Evolution Aqua Ltd Koi Pond Filters Pond Filtration ... Evolution Aqua Ltd, Evolution House, Kellet Close, Wigan, UK, WN5 0LP. contact us on tel: +44 (0)1942 216554 fax: +44 (0)1942 418 489 email: ...
Selection coefficients as function of antibiotic concentrations during competition experiments between strains carrying chromosomally carried resistance genes a
Our findings raise a very interesting theoretical problem - in a large genome, how do the millions of low-impact (yet functional) nucleotides arise? It is universally agreed that selection works very well for high-impact mutations. However, unless some new and as yet undiscovered process is operating in nature, there should be selection breakdown for the great majority of mutations that have small impact on fitness. We have now shown that this applies equally to both beneficial and deleterious mutations, and we have shown that selection interference is especially important when there are high-impact beneficial mutations. We conclude that only a very small fraction of all non-neutral mutations are selectable within large genomes. Our results reinforce and extend the findings of earlier studies [1-13], which in general employed many simplifying assumptions and rarely included more than a single source of biological noise. We show that selection breakdown is not just a simple function of population ...
Author Summary The diversity of life is a consequence of changes in the genotype (genes and their interdependence), but it is upon the observable organisms morphology (phenotype) that natural selection acts. Thus, the study of genotype-phenotype mapping can reveal key mechanisms driving lifes capacity of continuous evolution and resilience in diverse environments. In this context, it has been observed that small numbers of genes form robust functional developmental modules, hierarchically reused throughout development. Here we analyze the evolution of small genetic modules toward higher diversity and robustness. Given the small size of the gene network, we can afford to analyze all possible topologies and thus the entire fitness landscape. This exhaustive study as well as simulations of evolutionary processes uncover a set of genetic interactions producing robust and diverse phenotypes. We single out the distinctive features of these networks responsible for their stability against environmental and
Natural selection, Darwin s hypothesized tool to explain the development of complexity in species, appeared to have been responsible in moving the species further apart, Presgraves found. He used statistical means to compare the amount of genetic divergence in Nup 96 that existed between the two species to the amount of divergence among individual members of the same species. Members of one species, which readily exchange genes, would indicate what the normal generation-to-generation rate of random genetic mutation would be. The difference between species, however, would show if any of the new randomly acquired traits were useful enough to be "selected for," and passed on to successive generations. While natural selection appeared to evidently play a major role in the development of Nup 96, Presgraves plans to investigate the other 20 or so genes that keep the two species separate, in order to have a full genetic picture of the species divergence ...
Most biologists take for granted the idea that all life evolved by natural selection over billions of years. They get on with researching and teaching in disciplines that rest squarely on that foundation, secure in the knowledge that natural selection is a fact, in the same way that the Earth orbits the Sun is a fact.. Given that the concepts and realities of Darwinian evolution are still challenged, albeit rarely by biologists, a succinct briefing on why evolution by natural selection is an empirically validated principle is useful for people to have to hand. We offer here 15 examples published by Nature over the past decade or so to illustrate the breadth, depth and power of evolutionary thinking. We are happy to offer this resource freely and encourage its free dissemination. ...
Assays to accurately estimate relative fitness of bacteria growing in multistrain communities can advance our understanding of how selection shapes diversity within a lineage. Here, we present a variant of the evolve and resequence approach both to estimate relative fitness and to identify genetic variants responsible for fitness variation of symbiotic bacteria in free-living and host environments. We demonstrate the utility of this approach by characterizing selection by two plant hosts and in two free-living environments (sterilized soil and liquid media) acting on synthetic communities of the facultatively symbiotic bacterium Ensifer meliloti We find ( i ) selection that hosts exert on rhizobial communities depends on competition among strains, ( ii ) selection is stronger inside hosts than in either free-living environment, and ( iii ) a positive host-dependent relationship between relative strain fitness in multistrain communities and host benefits provided by strains in single-strain ...
View Notes - Lecture 5 figs from PCB 4674 at University of Florida. 2" o r: Mutation rates: 3 0.8 A a 0.0001 (n) 55 a A 0.00001 (v) 2* 0.6 3 8* 04 Equilibrium frequency: J: p = 0.091 .9
A simple way to operationalize natural selection would be to count progeny, or more specifically, to count viable, fertile progeny. If this is the understanding-that natural selection means relative reproductive success in the same way that hunger means two or more days without food, that is, if natural selection is operationalized in terms of empirical observations and statistical thresholds-then the term would have a noncontroversial conventionalized usage (with potentially other thresholds established to define genetic drift, and maybe others bad luck or acts of God). But if "natural selection" denotes a process that cannot be operationalized in this or some other way, then the concept of natural selection, whatever merits it might possess, is not a scientific concept, but an example of the nominal fallacy, in which the christening of something with a name (e.g., natural selection) mistakenly is taken to be an explaining of the thing (e.g., evolutionary outcomes ...
All they are showing is an example of natural selection, not evolution. The mouse is still a mouse. Through natural selection, a CHARACTERISTIC of the mouse changed, but at its core, it is still a mouse. That is like pointing out how people closer to the equator have darker skin as opposed to those in more temperate climates. They are adapted to their environments, but it doesnt make any of them any less human. No REAL mutation can add any information (like changing a mouse into a newt). It has been shown time and time again that mutations of this sort are degenerate (and therefor would cause the organism in question to cease to exist). Evolution requires millions of years of coincidental POSITIVE mutations to occur in order to achieve complex organisms... right. At the end of the day, its still just a mouse with a different characteristic due to natural selection (or in this case humans making the selection which would actually be by design ...
Jesús is from México, and works as a Postgraduate Researcher in the Uauy group, where he tries to elucidate the impact of artificial selection on haplotype…
Darwinian Natural Selection Motivation Most powerful mode of evolution Explains observation of Descent with Modification Nonrandom survivorship/reproduction of individuals based on particular features of their phenotype. Any environmental agent may be the cause of natural selection Slideshow 793925 by tejana
The neutral theory of molecular evolution predicts that the amount of neutral polymorphisms within a species will increase proportionally with the census population size (Nc). However, this prediction has not been borne out in practice: while the range of Nc spans many orders of magnitude, levels of genetic diversity within species fall in a comparatively narrow range. Although theoretical arguments have invoked the increased efficacy of natural selection in larger populations to explain this discrepancy, few direct empirical tests of this hypothesis have been conducted. In this work, we provide a direct test of this hypothesis using population genomic data from a wide range of taxonomically diverse species. To do this, we relied on the fact that the impact of natural selection on linked neutral diversity depends on the local recombinational environment. In regions of relatively low recombination, selected variants affect more neutral sites through linkage, and the resulting correlation between ...
A type of selection that removes individuals from the center of a phenotypic distribution and thus causes the distribution to become bimodal. This occurs when natural selection favours both ends of the phenotypic variation. Over time, the two extreme variations will become more common and the intermediate states will be less common or lost. Disruptive selection can lead to two new species. Light coloured and dark coloured mice might live in an environment with patches of light and dark vegetation making it hard for predators to spot those colours, while the middle coloured mouse doesnt blend into either background ...
Natural selection does not lead to continual improvement (evolution); it only helps to maintain features that organisms already have (creation).
Natural selection: Natural selection, process in which an organism adapts to its environment by means of selectively reproducing changes in its genotype.
In article ,90luod$kkb$1 at mercury.hgmp.mrc.ac.uk,, James McInerney ,james.o.mcinerney at may.ie, wrote: ,I have a question about selection on genes in HIV (but probably anywhere). ,In some HIV genes there is often a great excess of replacement substitutions ,over silent substitutions. In the past we would say that this meant that ,there was a positive selection event involved. However, if there is no ,selective difference between substitutions that occur in synonymous and ,non-synonymous sites then we would see about three times as many ,substitutions that are replacement than silent. I believe such studies generally take this into account. They reckon up how many sites *could* have a synonymous or nonsynonymous (S and N from here on) substitution, and weight by how many such substitutions could occur (a fourfold degenerate site contributes more possible S substitutions than a twofold ones). So the actual statistic is the ratio of S mutations per S site and N mutations per N site. This is ...
The Origin of Species by Means of Natural Selection Or, The Preservation of Favoured Races in the Struggle for Life By Charles Darwin: "If green woodpeckers alone had existed and we did not know that there were many black and pied kinds I dare say that we should have thought that the green colour was a beautiful adaptation to conceal this tree frequenting bird from its enemies and consequently that it was a character of importance and had been acquired through natural selection. As it is the colour is probably in chief part due to sexual selection. A trailing palm in the Malay Archipelago climbs the loftiest trees by the aid of exquisitely constructed hooks clustered around the ends of the branches and this contrivance no doubt is of the highest service to the plant but as we see nearly similar hooks on many trees which are not climbers and which as there is reason to believe from the distribution of the thorn bearing species in Africa and South America serve as a defence against browsing ...
3. The last point we discussed, which is maybe the most interesting, is the issue of the "infinitesimal model". The "infinitesimal model," originated by Fisher, assumes that contributions to the genetic variance are additive, relatively small and coming from many loci. The multiplication of QTL studies and other genomic approaches this last years has led to numerous discussions questioning this model, assuming that the reason for the lack of evidence for phenotypic traits controlled by few loci was more or less technological. We have ourselves discussed this issue in this very blog including when studies about human height and some QTLs found to explain just a few percents of variation. Well in light of this article it seems that it is again the case in drosophila, as control for height is seems to be largely polygenic, and the estimates presented here are even a low estimate as the methodology used is quite conservative (polymorphisms with population frequencies under 10% were not even analyzed ...
Major controversies in science have a way of appearing obvious in retrospect. We find it hard to understand why smart people took so long to agree that the earth revolves around the sun, that glaciers once covered the northern latitudes, that the continents drift, and that species are derived from other species.. So it is with group selection, a theory that was declared dead in the 1960s, only to come to life as an essential tool for understanding animal and human societies. Group selection theory employs the following assumptions.. 1) Natural selection is based on relative fitness.. 2) Selection among individuals within groups tends to favor traits that are called selfish in human terms; that is, traits that benefit individuals at the expense of other members of the group and the group as a whole.. 3) The evolution of group-advantageous traits typically requires a process of selection among groups in a multi-group population.. 4) Groups are defined as the individuals who influence each others ...
An organisms genome is continually being alteredby mutations, the vast majority of which are harmful to the organism or its descendants, because they reduce the bearers viability or fertility
The Theory of Natural Selection can be thought of an on-going cycle whereby generations of populations encounter an ever changing environment that selects winners and losers. To the winners Plan your 60 minutes lesson in Science or natural selection (Evolution) with helpful tips from Mitchell Smith
One can ask similar questions about crystals or small organic molecules. For the latter one can similarly show that the number is much more than the number of atoms in the universe. But most naturally occurring organic molecules have a preponderance of certain fragments like benzene rings. Similarly, there are only a certain rather small number of symmetry groups for crystals. Therefore it seems that in reality, we are dealing with modular units which are much smaller in number (although still quite large) rather than the bare individual units which compose proteins/small molecules/crystals. Thus once these modular units evolved, natural selection probably worked on them instead of trying out possible combinations of their individual atoms. Also remember that natural selection can work on a population of individuals- any kind of individuals- if one of them shows even the slightest advantage with respect to replication. In case of sequences of amino acids, such replicative advantages could arise ...
This tutorial first establishes the conditions for natural selection to operate, and distinguishes directional, stabilizing, and disruptive forms of selection. We then consider how widely in nature the conditions are met, and review the evidence for variation within species; the review begins at the level of gross morphology and works down to molecular variation. Variation originates by recombination and mutation, and we finish by looking at the argument to show that when new variation arises it is not directed toward improved adaptation.. ...
The very notion that actions are selected is controversial. One difficulty is that the concept of action selection, at least as traditionally defined, assumes the decomposition of behavior into distinct elements (actions) that can be selected between. Whilst it is possible to design an artefact, such as a robot, to have a repertoire of discrete acts that it can perform, it is not immediately clear that animal or human behavior decomposes cleanly in this way. For instance, what constitutes an action when you reach for, grasp, and then sip from a glass of water? On one view you might be performing a sequence of three separate acts-reach, grasp, sip-on another you are performing a single integrated act of drinking. This issue is not merely a descriptive one. On the hypothesis that the brain is solving action selection problems in executing such behaviors, a critical question concerns what the units of selection might be. In this example, you might select to take a drink and then resolve a ...
Heritability is often the single most important metric in deciding whether a given phenotype is worth probing for contributing genes and pathways, although as Walsh and Blows point out (47), there are very few traits which have a heritability of zero. It is of some interest that the h2 for the selected lines was lowest for response to training, ΔDIST (0.10) relative to h2 for distances (DIST) and body weights both before and after training (Tables 2 and 3). One interpretation is that response to exercise (i.e., an adaptation to environment) is more tightly linked with evolutionary fitness. That is, based on Fishers 1930 Theorem of Natural Selection (16), traits peripherally associated with evolutionary fitness, such as morphology and complex physiology, retain more additive genetic variance because of less pressure from natural selection.. An alternative way of looking at the low heritability of ΔDIST is to put it into the context of the genetics of its components. Using a selection index ...
The evolution of complex life forms seems to be inextricably tied to robustness. The problem of how complexity, modularity, adaptation and reliability are connected is an old one (Conrad 1983) but far from being closed (,Hogeweg 2002; ,Lenski et al. 2003; ,Wagner et al. 2007). Capturing the details of such relations is a difficult task, and theoretical approaches require strong simplifications that are typically based on a computational picture of the system under consideration. In this paper, we have explored the possible origins of robustness in networks performing computations by using evolved artificial circuits. Although the approach taken is not a realistic biological implementation, it captures some of the logic of cellular networks at least at the level of computation. Nevertheless, our main goal was to determine the possible forms of reaching reliable systems under different selection pressures and understanding how robust designs can be obtained. Given the two potential origins of ...
Most people are familiar with the term natural selection. Most people can even use it in a phrase: How do I know Darwin was right? Well, natural selection of course! However, most people cant describe precisely what it is or how it works. Let alone discuss its limitations. In the 1800s a young Charles Darwin…
Malaria parasites in mosquito midgut Why is it so hard to come up with a disproof (or a proof) of overdominant selection in MHC? Im starting kind of in mid
Click the video to see an octopus mimic algae. Octopuses have an amazing ability to sense and mimic the coloration, shape, and texture of their surroundings. They literally "blend in" as the video illustrates. Note how the audience appropriately responds at the end of the video. You can read more about this amazing ability here. The idea that such mimicry evolved is unlikely. The problem is that evolutions random mutations are not up to the task. Too many of them are required. And no, natural selection doesnt make it happen. Selection cannot coax, cajole, persuade or otherwise sweet talk mutations into happening. Selection is simply a label for what happens afterwards: in a word, harmful mutations are eliminated. Indeed, evolution co-founder Alfred Wallace thought the term "natural selection" should be dropped altogether, because it really doesnt do anything and so is misleading. According to evolutionary theory, selection can have no forward influence on mutations. It cannot cause helpful ...
I ended my talk at the CIfAR Integrated Microbial Diversity meeting by asking how much variation we should expect in core bacterial genes within a single species, and I considered this more at lab meeting yesterday. We see a lot of variation in competence phenotypes, due, we assume, to variation in the corresponding genes. But we dont know if this variation is telling us something particular about how selection acts on DNA uptake and transformation, or is just normal ...
... One of the first adaptations of evolution should have been a non-random process of mutation. -
Natural selection leads to evolution because the traits of those who are able to reproduce influence future generations genetics and gradually lead to these passed on traits becoming the normal state...