Natural selection can be referred to as a process through which biological traits turn either more or less common within a population as a function of the impact of hereditary traits on the differential reproductive victory of organisms’ interaction with their surroundings. It is a major evolution mechanism. Charles Darwin popularized the term natural selection with an intention to have it compared with artificial selection, now referred to as selective breeding.
There exists variation within every organism’s populations. This takes place partly since random mutations happen in the genome of an organism, and these mutations can be acquired by offspring. All through the lives of an individual, their genomes do interact with their surroundings to contribute to variations in traits. The genome’s environment includes the molecular biology in the cell, other individuals, species, populations, other cells, as well as the abiotic surroundings. People with some variants of the trait can endure and reproduce more individuals with other variants. Thus, the population undergoes evolution. Factors, which cause effects on reproductive success are also crucial, an issue that was developed by Charles Darwin in his thoughts on sexual selection.
Natural selection follows up on the phenotype, or features of an organism that are observable, although the genetic foundation of any phenotype that offers a reproductive benefit may turn more ordinary in a population. With time, this procedure can lead to populations, which specialize for certain ecological niches and may finally cause the new species emergence. Otherwise stated, natural selection is a crucial procedure through which evolution occurs within an organism’s population. Natural selection may be counterpointed with artificial selection, where human beings deliberately choose certain traits. There exists no deliberate choice in natural selection. In other words, artificial selection can be said to be teleological while natural selection is not.
Natural selection is among the bases of advanced biology. The Darwin introduced the term in his influential book (Darwin) in which he depicted natural selection as correspondent to artificial selection, a procedure through which plants and animals with features regarded as desirable by human breeders are favored systematically for reproduction. The natural selection concept was initially developed without a valid heredity theory. The traditional Darwinian evolution union with succeeding discoveries in molecular as well as classical genetics is referred to as the modern evolutionary synthesis. Natural selection is still the main account for adaptive evolution.
Natural variation takes place among the people of any organism’s population. Majority of these differences cause no effect on survival, though a number of differences may enhance the probabilities of survival of a certain individual. Something, which raises a chance of an animal's survival will frequently also include its rate of reproduction. Nevertheless, at times there exists a trade-off between current reproduction and survival. Eventually, what counts is the animal’s total lifetime reproduction.
If the features that offer these individuals a reproductive benefit are as well heritable, meaning that it is passed from a parent to a child, then there will be a marginally higher part of the feature in the generation that follows. This is referred to as differential reproduction. Although the reproductive benefit is very small, over several generations any heritable benefit will turn to be prevalent in the population. In this manner an organism’s natural surroundings selects for features that give a reproductive benefit, making slow changes or life evolution. Charles Darwin was the one who initially depicted as well as named this effect.
The natural selection concept predates the apprehension of genetics, the heredity mechanism for every known life form. In current terms, selection acts on the phenotype of an organism, but it is the genetic make-up of an organism that is hereditary. The phenotype is the outcome of the genotype together with the environment in which the organism inhabits.
This is the association between genetics and natural selection, as depicted in the modern evolutionary synthesis. Even though a whole evolution theory also needs an account of the way genetic variation develops originally and includes other mechanisms of evolution, natural selection seems to be the most essential mechanism for the creation of complex adaptations in nature.
Natural selection may act on any inheritable phenotypic characteristic, and selective pressure may be given by any facet of the environment, which includes sexual selection as well as competition with similar or different species members. Nevertheless, this does not mean that natural selection is forever directional and leads to adaptive evolution. Natural selection frequently causes the preservation of the status quo through elimination of less fit variants.
The selection unit may be the individual or it may be another stage within the biological organization hierarchy, like cells, genes, as well as kin groups. A debate exists about whether natural selection performs at the species or groups level to give adaptations, which gain a larger, non-kin group. Similarly, a debate exist on whether selection at the molecular level before gene mutations and zygote fertilization ought to be assigned to conventional natural selection since traditional natural selection is an environmental as well as an outside force, which acts on a phenotype characteristically following birth. Several scientists differentiate gene selection from natural selection through informal referencing of selection of mutations as pre-selection.
Different level selection like the gene may cause a rise in that gene’s fitness, whereas simultaneously lowering the fitness of the organism with that gene, in a procedure referred to as intragenomic conflict. In general, the compounded effect of every selection pressure at several levels influences the general fitness of an organism, and thus the natural selection outcome.
Natural selection happens at all life stages of an organism. An organism has to survive till maturity prior to reproduction, and selection of those that attain this level is referred to as viability selection. In several species, grownups have to engage into a competition with one another for mates through sexual selection, and victory in this competition influences parent of the next generation. When organisms can reproduce over one time, a longer survival in the phase of reproduction raises the offspring number, termed survival selection.
The fecundity of both males and females like giant sperm in some Drosophila species (Pitnick and Markow) can be restricted through fecundity selection. The produced gametes viability can vary, while intragenomic conflicts like meiotic drive between the haploid gametes can cause genic or gametic selection. Eventually, the pairing of some eggs and sperm combinations may be more simpatico than others. This is referred to as compatibility selection.
Ecological selection covers any selection mechanism occurring due to the environment which includes competition, kin selection and infanticide. Sexual selection, on the other hand, refers particularly to the competition for a mating partner (Andersson). This competition can be intrasexual where competition occurs among the individuals belonging to the same sex in a given population. The competition can also be intersexual where one sex has control over reproductive access by determining the best among the available mats. In most cases intrasexual selection is involved with a male to male competition and intersexual selection is involved with a selection of the suitable male by female. Selection of a suitable male by female in intersexual selection is mainly due to the greater resource investment for a female than for a male to give a single offspring.
There are, however, some species that show sex-role reversed behavior where the males are the ones who are the most selective in choosing a mate. One example that is well known for this behavior is the in the fish family known as Syngnathidae. Other likely examples have also been identified in birds and amphibian (Eens and Pinxten). Some of the features that are limited to one sex in a particular species have been explained through selection applied by the other sex in choosing a mate. For instance, the extravagant plumage observed in some male birds. In a similar manner, aggression that occurs between members belong to the same sex is in some cases associated with very unique features, like the antlers of stags used in dealing with other stags. In a more general view, intrasexual selection is usually linked to sexual dimorphism which includes body size differences between males and females in a given species (Barlow).
There are several examples of natural selection including increased antibiotic resistance via the survival of those who are immune to the effects caused by the antibiotic. The offspring of such individuals inherit the resistant trait and this creates new population bacteria that are resistant to antibiotic. The natural bacteria populations contain among them a considerable number of variations in their genetic makeup mainly due to mutations. Exposing these bacteria to antibiotic eliminates most of them with some that have specific mutations are less susceptible to the antibiotics. If the antibiotic exposure is short, these individuals with resistance will survive the medication. Such selective elimination of the individuals who are maladapted from the population is the natural selection.
Those bacteria that survive may then reproduce to give the next generation. Since the maladapted individuals have been removed in the previous generation, the new generation has more bacteria that have the resistance against the given antibiotic. In addition, there are new mutations that occur and this result to new genetic variations to existing genetic ones. In bacteria, the occurrence of spontaneous mutations is rare and advantageous mutations being even rarer. However, bacteria population is large enough to enable a few individuals to possess the beneficial mutations. If the new mutation results to reduction in antibiotic susceptibility, these individuals have a higher chance of surviving they are confronted with the same antibiotic.
With enough time and repetitive exposure to antibiotics, there are chances that a population that is resistant to the antibiotic may arise. This new population that has resistant to antibiotic is best adapted to the context where it evolved. This population may not be optimally adapted to environments that are free from antibiotics. Natural selection, therefore, results to two different populations that are optimally adapted to specific conditions, while they perform poorly in the other conditions. Excessive use and misuse of antibiotics has led to raised levels of microbial resistance to the antibiotics that are used clinically (Schito). This has also resulted to an evolutionary arms race where microbes continue to develop strains less susceptible to antibiotics, and at the same time medical researchers continue with the development of antibiotics that are capable of killing these microbes. This arms race is not only induced by man since there are cases where spreading of gene occurs over a short period of time (Sylvain, Emily and James).
The way life arose is still a problem that is unresolved in biology. A prominent thought is that life initially came along in the kind of short RNA polymers that are self-replicating (Eigen, Gardiner and Schuster). On this opinion, life may have originated when chains of RNA initially went through the basic conditions, as believed by Darwin, for natural selection to function. These conditions include variation of type, competition for limited resources, and heritability. Fitness of an early RNA replicator would probably have been an adaptive capacities function, which were intrinsic and the resources availability (Michod). The three main adaptive capacities could rationally have been the capacity to replicate with reasonable fidelity, the capacity to keep away from decay, and the capacity to obtain and process resources. These capacities would have been influenced at first by the folded configurations of the RNA replicators, which, successively, would have been encoded in their individual sequences of nucleotide. Competitive success in dissimilar RNA replicators would have relied on their adaptive capacities’ relative values.
Wilhelm Roux, a modern embryology founder, in the 19th century, wrote a book in which he proposed that an organism’s development arises from a
Darwinian competition between the embryo parts, happening at all stages, from molecules to organs. This theory’s modern version has since been suggested by Jean-Jacques Kupiec. Based on this cellular Darwinism, the molecular level stochasticity gives diversity in cell types while cell interactions enforce a typical order on the embryo that is developing.
The evolution theory’s social implications by natural selection also turned to be the source of ongoing controversy. Natural selection interpretation as necessarily progressive, causing rising advances in civilization and intelligence was used as an explanation for colonialism and eugenics policies, and broader sociopolitical views now depicted as Social Darwinism. There has been work by psychologists and anthropologists that has resulted in the development of sociobiology and afterward evolutionary psychology, a field attempting to give details of human psychology features in terms of the ancestral environment adaptation. A good example is the theory that the brain of the human is adapted to obtain the natural language grammatical rules (Pinker). In 1922, it was proposed by Alfred Lotka that natural selection may be apprehended as a physical principle that could be depicted in terms of the energy use by a system. This concept was later advanced by Howard Odum as the principle of maximum power whereby systems of evolution with selective benefit maximize the useful energy transformation rate.
The natural selection principles have inspired various computational techniques, for instance soft artificial life, which trigger selective processes and may be highly effectual in adapting units to a surrounding defined by specified function of fitness. For instance, a heuristic optimization algorithms class referred to as genetic algorithms, started by John Holland in the 1970s. It was expanded upon by David E. Goldberg who keyed out optimal solutions through simulated reproduction as well as mutation of a population of solutions defined by an original probability distribution. Such algorithms are especially helpful when used to problems whose landscape of solution is rough or has several local minima.
The natural selection idea predates the apprehension of genetics. There is now a better idea of the biology behind heritability, which is the natural selection basis. Natural selection acts on a phenotype of an organism. Phenotype is influenced by a genotype of an organism and the surrounding in which the organism inhabits. Frequently, natural selection acts on specific characteristics of an individual that are indicated by the terms phenotype and genotype.
When different individuals in a population have different gene versions for a particular trait, version is referred to as an allele. It is this variation in genes that underlies phenotypic characteristics. A characteristic example is that some gene combinations for eye color in humans produce the blue eyes phenotype. Some characteristics are ruled by only a one gene, but the majority of traits are determined by many genes interactions. A deviation in one of the several genes that lead to a characteristic may have just a small impact on the phenotype. Combined, these genes can give a continuum of likely phenotypic values (Falconer and Mackay).
When a component of a trait is hereditary, selection will change the occurrence of the different alleles, or gene variants that give rise to the trait’s variants. Selection can be categorized into three groups based on its effect on frequencies of an allele (Rice). Directional selection happens when a particular allele has a more fitness than the rest, causing a rise in its frequency. This procedure can go on until the allele is fixed and the whole population shares the fitter observable traits. Stabilizing selection reduces the occurrence of alleles, which have a harmful effect on the phenotype. This procedure can go on until the allele is gotten rid of from the population. Stabilizing selection leads to functional genetic traits, like genes coding for protein or regulatory sequences, being preserved over time because of selective pressure against harmful variants. Balancing selection does not cause fixation, but preserves an allele at intermediate occurrences in a population. This can happen in diploid species when heterozygote organisms, with different alleles on every chromosome at one genetic locus, have a higher fitness than the homozygous ones of the same alleles. This is referred to as heterozygote benefit or over-dominance.
A part of all genetic variation is neutral, functionally, meaning that it gives no phenotypic effect or important difference in fitness. Natural selection leads to the decrease in genetic variation via the removal of maladapted individuals and as a result of the mutations that led to the mal-adaptation. Simultaneously, new mutations happen, leading to a balance in mutation-selection. The exact result of the two procedures relies on the rate of occurrence of new mutations and on the natural selection strength. As a result, modifications in the rate of mutation or the pressure of selection will lead to a different balance of mutation-selection.
Genetic linkage takes place when there is linking of loci belonging to two alleles or is placed in close proximity one loci to the other. During gamete formation, recombination of genetic material leads to reshuffling of the alleles. The occurrence of such a reshuffle between two alleles is dependent on the distance that separates the two alleles. Consequently, when selection aims one allele, the other allele is automatically selected. This kind of selection may result in a strong influence on the variation patterns that occur in the genome. Selective sweeps on the other hand take place when alleles are more common in a population due to positive selection. Increase in the prevalence of one allele results to the linked alleles becoming more common whether they are slightly deleterious or neutral. This is known as genetic hitchhiking. The opposite of selective sweep is the background selection. When a given site goes through a strong and persistent selection the linked variation tends to be combed out together with it. This produces a region of low overall variability in the genome. Background selection occurs due to deleterious new mutations that take place in any haploid randomly. This causes background selection not to produce clear linkage disequilibrium blocks. However, with low recombination it is possible to result to slightly negative linkage disequilibrium (Keightley and Otto).
Andersson, M. Sexual Selection. Princeton, New Jersey: Princeton University Press, 1995.
Barlow, G. W. "How Do We Decide that a Species is Sex-Role Reversed?" The Quarterly Review of Biology 80 .1 (2005): 28–35.
Darwin, C. On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. London: John Murray, 1859.
Eens, M. and R. Pinxten. "Sex-role reversal in vertebrates: behavioural and endocrinological accounts." Behav Processes 51.1-3 (2000): 135–147.
Eigen, M., et al. "The origin of genetic information." Sci Am 244.4 (1981): 88-92, 96.
Falconer, D. S. and T. F. C. Mackay. Introduction to Quantitative Genetics Addison. Harlow, Essex, UK: Wesley Longman, 1996.
Keightley, P. D. and S. P. Otto. "Interference among deleterious mutations favours sex and recombination in finite populations." Nature 443.7107 (2006): 89–92.
Michod, R. E. Darwinian Dynamics: Evolutionary Transitions in Fitness and Individuality. Princeton, New Jersey: Princeton University Press, 2000.
Pinker, S. The Language Instinct: How the Mind Creates Language. New York, NY, USA: HarperCollins, 1995.
Pitnick, S. and T. A. Markow. "Large-male advantage associated with the costs of sperm production in Drosophila hydei, a species with giant sperm." Proc Natl Acad Sci USA 91 (1994): 9277-81.
Rice, S. H. Evolutionary Theory: Mathematical and Conceptual Foundations. Sunderland, Massachusetts, USA: Sinauer Associates, 2004.
Schito, G. C. "The importance of the development of antibiotic resistance in Staphylococcus aureus." Clin Microbiol Infect 12.Suppl 1 (2006): 3–8.
Sylvain, Charlat, et al. "Extraordinary flux in sex ratio." Science 317.5835 (2007): 214.