. Natural selection is the differential survival and reproduction of individuals due to differences in. It is a key mechanism of, the change in the characteristic of a over generations. Popularised the term 'natural selection', contrasting it with, which is intentional, whereas natural selection is not. Exists within all populations of.
This occurs partly because random arise in the of an individual organism, and can inherit such mutations. Fundamentals of investing gitman solutions manual. Throughout the lives of the individuals, their genomes interact with their environments to cause variations in traits. The environment of a genome includes the molecular biology in the, other cells, other individuals, populations, as well as the abiotic environment. Because individuals with certain variants of the trait tend to survive and reproduce more than individuals with other, less successful variants, the population evolves. Other factors affecting reproductive success include (now often included in natural selection) and. Natural selection acts on the phenotype, the characteristics of the organism which actually interact with the environment, but the (heritable) basis of any phenotype that gives that phenotype a reproductive advantage may become.
Over time, this process can result in populations that specialise for particular and may eventually result in (the emergence of new species, ). In other words, natural selection is a key process in the evolution of a population. Natural selection is a cornerstone of modern. The concept, published by Darwin and in a, was elaborated in Darwin's influential 1859 book. He described natural selection as analogous to artificial selection, a process by which animals and plants with traits considered desirable by human breeders are systematically favoured for reproduction.
The concept of natural selection originally developed in the absence of a valid theory of heredity; at the time of Darwin's writing, science had yet to develop modern theories of genetics. The union of traditional with subsequent discoveries in formed the of the mid-20th century. The addition of has led to, which explains evolution at the molecular level.
While can slowly change by random, natural selection remains the primary explanation for. Considered whether different forms could have appeared, only the useful ones surviving. Several philosophers of the, including and his intellectual successor, the poet, expressed the idea that nature produces a huge variety of creatures, randomly, and that only those creatures that manage to provide for themselves and reproduce successfully persist.
Empedocles' idea that organisms arose entirely by the incidental workings of causes such as heat and cold was criticised by in Book II of. He posited natural in its place, and believed that form was achieved for a purpose, citing the regularity of heredity in species as proof. Nevertheless, he accepted that new types of animals, (τερας), can occur in very rare instances (, Book IV).
As quoted in Darwin's 1872 edition of, Aristotle considered whether different forms (e.g., of teeth) might have appeared accidentally, but only the useful forms survived: So what hinders the different parts of the body from having this merely accidental relation in nature? As the teeth, for example, grow by necessity, the front ones sharp, adapted for dividing, and the grinders flat, and serviceable for masticating the food; since they were not made for the sake of this, but it was the result of accident.
And in like manner as to the other parts in which there appears to exist an adaptation to an end. Wheresoever, therefore, all things together (that is all the parts of one whole) happened like as if they were made for the sake of something, these were preserved, having been appropriately constituted by an internal spontaneity, and whatsoever things were not thus constituted, perished, and still perish. — Aristotle, Physics, Book II, Chapter 8 But Aristotle rejected this possibility in the next paragraph, making clear that he is talking about the development of animals as embryos with the phrase 'either invariably or normally come about', not the origin of species. Yet it is impossible that this should be the true view. For teeth and all other natural things either invariably or normally come about in a given way; but of not one of the results of chance or spontaneity is this true. We do not ascribe to chance or mere coincidence the frequency of rain in winter, but frequent rain in summer we do; nor heat in the dog-days, but only if we have it in winter. If then, it is agreed that things are either the result of coincidence or for an end, and these cannot be the result of coincidence or spontaneity, it follows that they must be for an end; and that such things are all due to nature even the champions of the theory which is before us would agree.
Therefore action for an end is present in things which come to be and are by nature. — Aristotle, Physics, Book II, Chapter 8 The was later described by the writer in the 9th century. The classical arguments were reintroduced in the 18th century by and others, including Darwin's grandfather,. Until the early 19th century, the in was that differences between individuals of a species were uninteresting departures from their (or ) of. However, the theory of in geology promoted the idea that simple, weak forces could act continuously over long periods of time to produce radical changes in the 's landscape.
The success of this theory raised awareness of the vast scale of and made plausible the idea that tiny, virtually imperceptible changes in successive generations could produce consequences on the scale of differences between species. The early 19th-century zoologist suggested the as a mechanism for evolutionary change; adaptive traits acquired by an organism during its lifetime could be inherited by that organism's progeny, eventually causing. This theory, was an influence on the Soviet biologist 's antagonism to mainstream genetic theory as late as the mid 20th century.
Between 1835 and 1837, the zoologist worked on the area of variation, artificial selection, and how a similar process occurs in nature. Darwin acknowledged Blyth's ideas in the first chapter on variation of On the Origin of Species. Darwin's theory.
Further information: In 1859, Charles Darwin set out his theory of evolution by natural selection as an explanation for and speciation. He defined natural selection as the 'principle by which each slight variation of a trait, if useful, is preserved'. The concept was simple but powerful: individuals best adapted to their environments are more likely to survive and reproduce. As long as there is some variation between them and that variation is, there will be an inevitable selection of individuals with the most advantageous variations. If the variations are heritable, then differential reproductive success leads to a progressive evolution of particular of a species, and populations that evolve to be sufficiently different eventually become different species.
Part of 's table of in England 1780–1810, from his, 6th edition, 1826 Darwin's ideas were inspired by the observations that he had made on the (1831–1836), and by the work of a political economist, who, in (1798), noted that population (if unchecked), whereas the food supply grows only; thus, inevitable limitations of resources would have demographic implications, leading to a 'struggle for existence'. When Darwin read Malthus in 1838 he was already primed by his work as a to appreciate the 'struggle for existence' in nature. It struck him that as population outgrew resources, 'favourable variations would tend to be preserved, and unfavourable ones to be destroyed. The result of this would be the formation of new species.'
— Darwin summarising natural selection in the fourth chapter of Once he had his theory, Darwin was meticulous about gathering and refining evidence before making his idea public. He was in the process of writing his 'big book' to present his research when the naturalist independently conceived of the principle and described it in an essay he sent to Darwin to forward to. Lyell and decided to present his essay together with unpublished writings that Darwin had sent to fellow naturalists, and was read to the announcing co-discovery of the principle in July 1858. Darwin published a detailed account of his evidence and conclusions in in 1859. In the 3rd edition of 1861 Darwin acknowledged that others—like in 1813, and in 1831—had proposed similar ideas, but had neither developed them nor presented them in notable scientific publications. Noted that had created many kinds of pigeon, such as (1, 12), (13), and (14). Darwin thought of natural selection by analogy to how farmers select crops or livestock for breeding, which he called '; in his early manuscripts he referred to a 'Nature' which would do the selection.
At the time, other mechanisms of evolution such as evolution by genetic drift were not yet explicitly formulated, and Darwin believed that selection was likely only part of the story: 'I am convinced that Natural Selection has been the main but not exclusive means of modification.' In a letter to Charles Lyell in September 1860, Darwin regretted the use of the term 'Natural Selection', preferring the term 'Natural Preservation'. For Darwin and his contemporaries, natural selection was in essence synonymous with evolution by natural selection. After the publication of On the Origin of Species, educated people generally accepted that evolution had occurred in some form.
However, natural selection remained controversial as a mechanism, partly because it was perceived to be too weak to explain the range of observed characteristics of living organisms, and partly because even supporters of evolution balked at its 'unguided' and non- nature, a response that has been characterised as the single most significant impediment to the idea's acceptance. However, some thinkers enthusiastically embraced natural selection; after reading Darwin, introduced the phrase, which became a popular summary of the theory. The fifth edition of On the Origin of Species published in 1869 included Spencer's phrase as an alternative to natural selection, with credit given: 'But the expression often used by Mr.
Herbert Spencer of the Survival of the Fittest is more accurate, and is sometimes equally convenient.' Although the phrase is still often used by non-biologists, modern biologists avoid it because it is if 'fittest' is read to mean 'functionally superior' and is applied to individuals rather than considered as an averaged quantity over populations. The modern synthesis. Main article: Natural selection relies crucially on the idea of heredity, but developed before the basic concepts of.
Although the monk, the father of modern genetics, was a contemporary of Darwin's, his work lay in obscurity, only being rediscovered in 1900. With the early 20th century integration of evolution with of inheritance, the so-called, scientists generally came to accept natural selection. The synthesis grew from advances in different fields.
Ronald Fisher developed the required mathematical language and wrote (1930). Introduced the concept of the 'cost' of natural selection. Elucidated the nature of selection and adaptation.
In his book (1937), established the idea that mutation, to selection, actually supplied the raw material for natural selection by creating genetic diversity. A second synthesis. Main article: recognised the key importance of for speciation in his (1942).
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Conceived of in 1964. This synthesis cemented natural selection as the foundation of evolutionary theory, where it remains today. A second synthesis was brought about at the end of the 20th century by advances in, creating the field of ('evo-devo'), which seeks to explain the evolution of in terms of the which control the development of the embryo at molecular level. Natural selection is here understood to act on embryonic development to change the morphology of the adult body. Terminology The term natural selection is most often defined to operate on heritable traits, because these directly participate in evolution. However, natural selection is 'blind' in the sense that changes in phenotype can give a reproductive advantage regardless of whether or not the trait is heritable.
Following Darwin's primary usage, the term is used to refer both to the evolutionary consequence of blind selection and to its mechanisms. It is sometimes helpful to explicitly distinguish between selection's mechanisms and its effects; when this distinction is important, scientists define '(phenotypic) natural selection' specifically as 'those mechanisms that contribute to the selection of individuals that reproduce', without regard to whether the basis of the selection is heritable.
Traits that cause greater reproductive success of an organism are said to be selected for, while those that reduce success are selected against. Mechanism Heritable variation, differential reproduction.
Main article: Natural variation occurs among the individuals of any population of organisms. Some differences may improve an individual's chances of surviving and reproducing such that its lifetime reproductive rate is increased, which means that it leaves more offspring. If the traits that give these individuals a reproductive advantage are also, that is, passed from parent to offspring, then there will be differential reproduction, that is, a slightly higher proportion of fast rabbits or efficient algae in the next generation. Even if the reproductive advantage is very slight, over many generations any advantageous heritable trait becomes dominant in the population.
In this way the of an organism 'selects for' traits that confer a reproductive advantage, causing evolutionary change, as Darwin described. This gives the appearance of purpose, but in natural selection there is no intentional choice. Artificial selection is where natural selection is not, though to describe it. The exists in both light and dark colours in Great Britain, but during the, many of the trees on which the moths rested became blackened by, giving the dark-coloured moths an advantage in hiding from predators. This gave dark-coloured moths a better chance of surviving to produce dark-coloured offspring, and in just fifty years from the first dark moth being caught, nearly all of the moths in industrial were dark. The balance was reversed by the effect of the, and the dark moths became rare again, demonstrating the influence of natural selection on.
A recent study, using image analysis and avian vision models, shows that pale individuals more closely match lichen backgrounds than dark morphs and for the first time quantifies the of moths to risk. Main article: The concept of fitness is central to natural selection. In broad terms, individuals that are more 'fit' have better potential for survival, as in the well-known phrase ', but the precise meaning of the term is much more subtle. Modern evolutionary theory defines fitness not by how long an organism lives, but by how successful it is at reproducing. If an organism lives half as long as others of its species, but has twice as many offspring surviving to adulthood, its genes become more common in the adult population of the next generation. Though natural selection acts on individuals, the effects of chance mean that fitness can only really be defined 'on average' for the individuals within a population. The fitness of a particular genotype corresponds to the average effect on all individuals with that genotype.
A distinction must be made between the concept of 'survival of the fittest' and 'improvement in fitness'. 'Survival of the fittest' does not give an 'improvement in fitness', it only represents the removal of the less fit variants from a population. A mathematical example of 'survival of the fittest' is given by Haldane in his 'The Cost of Natural Selection' paper.
Haldane called this process 'substitution' or more commonly in biology, this is called 'fixation'. This is correctly described by the differential survival and reproduction of individuals due to differences in phenotype.
On the other hand, 'improvement in fitness' is not dependent on the differential survival and reproduction of individuals due to differences in phenotype, it is dependent on the absolute survival of the particular variant. The probability of a beneficial mutation occurring on some member of a population depends on the total number of replications of that variant. The mathematics of 'improvement in fitness was described by Kleinman. An empirical example of 'improvement in fitness' is given by the Kishony Mega-plate experiment. In this experiment, 'improvement in fitness' depends on the number of replications of the particular variant for a new variant to appear that is capable of growing in the next higher drug concentration region. Fixation or substitution is not required for this 'improvement in fitness'.
On the other hand, 'improvement in fitness' can occur in an environment where 'survival of the fittest' is also acting. The classic Lenski 'E.
Coli long-term evolution experiment' is an example of adaptation in a competitive environment, ('improvement in fitness' during 'survival of the fittest'). The probability of a beneficial mutation occurring on some member of the lineage to give improved fitness is slowed by the competition. The variant which is a candidate for a beneficial mutation in this limited carrying capacity environment must first out-compete the 'less fit' variants in order to accumulate the requisite number of replications for there to be a reasonable probability of that beneficial mutation occurring.
Competition. 1:: a single extreme favoured. 2,: intermediate favoured over extremes.
3: disruptive selection: extremes favoured over intermediate. X-axis: Y-axis: number of organisms Group A: original population Group B: after selection Natural selection can act on any heritable, and selective pressure can be produced by any aspect of the environment, including sexual selection and with members of the same or other species. However, this does not imply that natural selection is always directional and results in adaptive evolution; natural selection often results in the maintenance of the status quo by eliminating less fit variants. Selection can be classified in several different ways, such as by its effect on a trait, on genetic diversity, by the life cycle stage where it acts, by the unit of selection, or by the resource being competed for. Selection has different effects on traits. Acts to hold a trait at a stable optimum, and in the simplest case all deviations from this optimum are selectively disadvantageous. Favours extreme values of a trait.
The uncommon also acts during transition periods when the current mode is sub-optimal, but alters the trait in more than one direction. In particular, if the trait is quantitative and then both higher and lower trait levels are favoured. Disruptive selection can be a precursor to. Alternatively, selection can be divided according to its effect on. Acts to remove genetic variation from the population (and is opposed by, which introduces new variation.
In contrast, acts to maintain genetic variation in a population, even in the absence of de novo mutation, by negative. One mechanism for this is, where individuals with two different alleles have a selective advantage over individuals with just one allele. The polymorphism at the human locus has been explained in this way. Different types of selection act at each of a sexually reproducing organism. Another option is to classify selection by the stage at which it acts. Some biologists recognise just two types:, which acts to increase an organism's probability of survival, and fecundity (or fertility or reproductive) selection, which acts to increase the rate of reproduction, given survival. Others split the life cycle into further components of selection.
Thus viability and survival selection may be defined separately and respectively as acting to improve the probability of survival before and after reproductive age is reached, while fecundity selection may be split into additional sub-components including sexual selection, gametic selection, acting on survival, and compatibility selection, acting on formation. Selection can also be classified by the level.
Individual selection acts on the individual, in the sense that adaptations are 'for' the benefit of the individual, and result from selection among individuals. Acts directly at the level of the gene. In and, gene-level selection provides a more apt explanation of the underlying process., if it occurs, acts on groups of organisms, on the assumption that groups replicate and mutate in an analogous way to genes and individuals. There is an ongoing debate over the degree to which group selection occurs in nature. Finally, selection can be classified according to the being competed for.
Sexual selection results from competition for mates. Sexual selection typically proceeds via fecundity selection, sometimes at the expense of viability. Is natural selection via any means other than sexual selection, such as kin selection, competition, and. Following Darwin, natural selection is sometimes defined as ecological selection, in which case sexual selection is considered a separate mechanism.
Sexual selection. Main article: Sexual selection as first articulated by Darwin (using the example of the 's tail) refers specifically to competition for mates, which can be intrasexual, between individuals of the same sex, that is male–male competition, or intersexual, where one gender, most often with males displaying and females choosing. However, in some species, mate choice is primarily by males, as in some fishes of the family.
Phenotypic traits can be in one sex and desired in the other sex, causing a loop called a, for example, the extravagant plumage of some male birds such as the peacock. An alternate theory proposed by the same in 1930 is the, that mothers want promiscuous sons to give them large numbers of grandchildren and so choose promiscuous fathers for their children. Aggression between members of the same sex is sometimes associated with very distinctive features, such as the antlers of, which are used in combat with other stags. More generally, intrasexual selection is often associated with, including differences in body size between males and females of a species. Natural selection in action. Further information: Natural selection is seen in action in the development of in.
Since the discovery of in 1928, have been used to fight bacterial diseases. The widespread misuse of antibiotics has selected for microbial resistance to antibiotics in clinical use, to the point that the (MRSA) has been described as a 'superbug' because of the threat it poses to health and its relative invulnerability to existing drugs. Response strategies typically include the use of different, stronger antibiotics; however, new of MRSA have recently emerged that are resistant even to these drugs. This is an, in which bacteria develop strains less susceptible to antibiotics, while medical researchers attempt to develop new antibiotics that can kill them. A similar situation occurs with in plants and insects. Arms races are not necessarily induced by man; a well-documented example involves the spread of a gene in the butterfly suppressing male-killing activity by bacteria parasites on the island of, where the spread of the gene is known to have occurred over a period of just five years Evolution by means of natural selection. Main articles: and A prerequisite for natural selection to result in adaptive evolution, novel traits and speciation is the presence of heritable genetic variation that results in fitness differences.
Genetic variation is the result of mutations, and alterations in the (the number, shape, size and internal arrangement of the ). Any of these changes might have an effect that is highly advantageous or highly disadvantageous, but large effects are rare. In the past, most changes in the genetic material were considered neutral or close to neutral because they occurred in or resulted in a. However, many mutations in non-coding DNA have deleterious effects.
Although both mutation rates and average fitness effects of mutations are dependent on the organism, a majority of mutations in humans are slightly deleterious. Some mutations occur in. Changes in these often have large effects on the phenotype of the individual because they regulate the function of many other genes. Most, but not all, mutations in regulatory genes result in non-viable embryos.
Some nonlethal regulatory mutations occur in in humans, which can result in a or, an increase in the number of fingers or toes. When such mutations result in a higher fitness, natural selection favours these phenotypes and the novel trait spreads in the population.
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Established traits are not immutable; traits that have high fitness in one environmental context may be much less fit if environmental conditions change. In the absence of natural selection to preserve such a trait, it becomes more variable and deteriorate over time, possibly resulting in a manifestation of the trait, also called. In many circumstances, the apparently vestigial structure may retain a limited functionality, or may be co-opted for other advantageous traits in a phenomenon known as. A famous example of a vestigial structure, the eye of the, is believed to retain function in perception.
Speciation. Main article: Speciation requires a degree of —that is, a reduction in gene flow. However, it is intrinsic to the concept of a that are selected against, opposing the evolution of reproductive isolation, a problem that was recognised by Darwin.
The problem does not occur in speciation with geographically separated populations, which can diverge with different sets of mutations. Realized in 1903 that reproductive isolation could evolve through divergence, if each lineage acquired a different, incompatible allele of the same gene. Selection against the heterozygote would then directly create reproductive isolation, leading to the, further elaborated by and. With, however, natural selection can favor an increase in pre-zygotic isolation, influencing the process of speciation directly. Genetic basis Genotype and phenotype. Main article: Natural selection acts on an organism's phenotype, or physical characteristics.
Phenotype is determined by an organism's genetic make-up (genotype) and the environment in which the organism lives. When different organisms in a population possess different versions of a gene for a certain trait, each of these versions is known as an. It is this genetic variation that underlies differences in phenotype. An example is the in humans, where three alleles govern the phenotype. Some traits are governed by only a single gene, but most traits are influenced by the interactions of many genes.
A variation in one of the many genes that contributes to a trait may have only a small effect on the phenotype; together, these genes can produce a continuum of possible phenotypic values. Directionality of selection. Main article: When some component of a trait is heritable, selection alters the frequencies of the different alleles, or variants of the gene that produces the variants of the trait. Selection can be divided into three classes, on the basis of its effect on allele frequencies: directional, stabilizing, and purifying selection. Directional selection occurs when an allele has a greater fitness than others, so that it increases in frequency, gaining an increasing share in the population.
This process can continue until the allele is and the entire population shares the fitter phenotype. Far more common is stabilizing selection, which lowers the frequency of alleles that have a deleterious effect on the phenotype – that is, produce organisms of lower fitness. This process can continue until the allele is eliminated from the population. Purifying selection functional genetic features, such as or, over time by selective pressure against deleterious variants. Some forms of balancing selection do not result in fixation, but maintain an allele at intermediate frequencies in a population. This can occur in species (with pairs of chromosomes) when individuals (with just one copy of the allele) have a higher fitness than homozygous individuals (with two copies). This is called heterozygote advantage or over-dominance, of which the best-known example is the resistance to malaria in humans heterozygous for.
Maintenance of allelic variation can also occur through, which favours genotypes that depart from the average in either direction (that is, the opposite of over-dominance), and can result in a of trait values. Finally, balancing selection can occur through frequency-dependent selection, where the fitness of one particular phenotype depends on the distribution of other phenotypes in the population. The principles of have been applied to understand the fitness distributions in these situations, particularly in the study of kin selection and the evolution of.
Selection, genetic variation, and drift. Main articles: and A portion of all genetic variation is functionally neutral, producing no phenotypic effect or significant difference in fitness. 's by proposes that this variation accounts for a large fraction of observed genetic diversity. Neutral events can radically reduce genetic variation through. Which among other things can cause the in initially small new populations. When genetic variation does not result in differences in fitness, selection cannot directly affect the frequency of such variation. As a result, the genetic variation at those sites is higher than at sites where variation does influence fitness.
However, after a period with no new mutations, the genetic variation at these sites is eliminated due to genetic drift. Natural selection reduces genetic variation by eliminating maladapted individuals, and consequently the mutations that caused the maladaptation. At the same time, new mutations occur, resulting in a. The exact outcome of the two processes depends both on the rate at which new mutations occur and on the strength of the natural selection, which is a function of how unfavourable the mutation proves to be.
Occurs when the of two alleles are in close proximity on a chromosome. During the formation of gametes, recombination reshuffles the alleles. The chance that such a reshuffle occurs between two alleles is inversely related to the distance between them. Occur when an allele becomes more common in a population as a result of positive selection.
As the prevalence of one allele increases, closely linked alleles can also become more common by ', whether they are neutral or even slightly deleterious. A strong selective sweep results in a region of the genome where the positively selected (the allele and its neighbours) are in essence the only ones that exist in the population. Selective sweeps can be detected by measuring, or whether a given haplotype is overrepresented in the population.
Since a selective sweep also results in selection of neighbouring alleles, the presence of a block of strong linkage disequilibrium might indicate a 'recent' selective sweep near the centre of the block. Is the opposite of a selective sweep. If a specific site experiences strong and persistent purifying selection, linked variation tends to be weeded out along with it, producing a region in the genome of low overall variability. Because background selection is a result of deleterious new mutations, which can occur randomly in any haplotype, it does not produce clear blocks of linkage disequilibrium, although with low recombination it can still lead to slightly negative linkage disequilibrium overall.
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Main article: Darwin's ideas, along with those of and, had a profound influence on 19th century thought, including his radical claim that 'elaborately constructed forms, so different from each other, and dependent on each other in so complex a manner' evolved from the simplest forms of life by a few simple principles. This inspired some of Darwin's most ardent supporters—and provoked the strongest opposition. Natural selection had the power, according to, to 'dethrone some of the deepest and most traditional comforts of Western thought', such as the belief that humans have a special place in the world. In the words of the philosopher, 'Darwin's dangerous idea' of evolution by natural selection is a 'universal acid,' which cannot be kept restricted to any vessel or container, as it soon leaks out, working its way into ever-wider surroundings. Thus, in the last decades, the concept of natural selection has spread from to other disciplines, including, and. This unlimited applicability has been called.
Origin of life. Main article: How life originated from inorganic matter remains an unresolved problem in biology.
One prominent hypothesis is that life first appeared polymers. On this view, life may have come into existence when chains first experienced the basic conditions, as conceived by Charles Darwin, for natural selection to operate. These conditions are: heritability, and competition for limited resources. The fitness of an early would likely have been a function of adaptive capacities that were intrinsic (i.e., determined by the ) and the availability of resources.
The three primary adaptive capacities could logically have been: (1) the capacity to replicate with moderate fidelity (giving rise to both heritability and variation of type), (2) the capacity to avoid decay, and (3) the capacity to acquire and process resources. These capacities would have been determined initially by the folded configurations (including those configurations with activity) of the RNA replicators that, in turn, would have been encoded in their individual nucleotide sequences. Cell and molecular biology In 1881, the embryologist published Der Kampf der Theile im Organismus ( The Struggle of Parts in the Organism) in which he suggested that the development of an organism results from a Darwinian competition between the parts of the embryo, occurring at all levels, from molecules to organs.
In recent years, a modern version of this theory has been proposed. According to this cellular Darwinism, at the molecular level generates diversity in cell types whereas cell interactions impose a characteristic order on the developing embryo. Social and psychological theory The social implications of the theory of evolution by natural selection also became the source of continuing controversy., a German and co-originator of the ideology of, wrote in 1872 that 'Darwin did not know what a bitter satire he wrote on mankind, and especially on his countrymen, when he showed that free competition, the struggle for existence, which the economists celebrate as the highest historical achievement, is the normal state of the animal kingdom.' Herbert Spencer and the eugenics advocate 's interpretation of natural selection as necessarily progressive, leading to supposed advances in intelligence and civilisation, became a justification for, and. For example, in 1940, in writings that he subsequently disowned, used the theory as a justification for policies of the state. He wrote '. selection for toughness, heroism, and social utility. Must be accomplished by some human institution, if mankind, in default of selective factors, is not to be ruined by domestication-induced degeneracy.
The racial idea as the basis of our state has already accomplished much in this respect.' Others have developed ideas that human societies and culture by mechanisms analogous to those that apply to evolution of species. More recently, work among anthropologists and psychologists has led to the development of and later of evolutionary psychology, a field that attempts to explain features of in terms of adaptation to the ancestral environment. The most prominent example of evolutionary psychology, notably advanced in the early work of and later by, is the hypothesis that the human brain has adapted to the rules of. Other aspects of human behaviour and social structures, from specific cultural norms such as to broader patterns such as, have been hypothesised to have similar origins as adaptations to the early environment in which modern humans evolved. By analogy to the action of natural selection on genes, the concept of —'units of cultural transmission,' or culture's equivalents of genes undergoing selection and recombination—has arisen, first described in this form by in 1976 and subsequently expanded upon by philosophers such as as explanations for complex cultural activities, including human. Information and systems theory In 1922, proposed that natural selection might be understood as a physical principle that could be described in terms of the use of energy by a system, a concept later developed by as the in, whereby evolutionary systems with selective advantage maximise the rate of useful energy transformation.
The principles of natural selection have inspired a variety of computational techniques, such as 'soft', that simulate selective processes and can be highly efficient in 'adapting' entities to an environment defined by a specified. For example, a class of known as, pioneered by in the 1970s and expanded upon by, identify optimal solutions by simulated reproduction and mutation of a population of solutions defined by an initial.
Such algorithms are particularly useful when applied to problems whose is very rough or has many local minima. In fiction.
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