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evidence history processes and outcomes population genetics quantitative genetics variation diversity mutation natural selection adaptation polymorphism genetic drift gene flow speciation adaptive radiation cooperation coevolution coextinction contingency divergence convergence parallel evolution extinction natural history origin of life common descent history of life timeline of evolution human evolution recent human evolution phylogeny biodiversity biogeography classification evolutionary taxonomy cladistics transitional fossil extinction event history of evolutionary theory overview scientific revolution before darwin darwin origin of species before synthesis modern synthesis molecular evolution evo devo current research history of speciation history of paleontology timeline fields and applications applications of evolution biosocial criminology ecological genetics evolutionary aesthetics evolutionary anthropology evolutionary ecology evolutionary economics evolutionary epistemology evolutionary ethics evolutionary game theory evolutionary linguistics evolutionary medicine evolutionary neuroscience evolutionary physiology evolutionary psychology experimental evolution invasion genetics island biogeography phylogenetics paleontology selective breeding speciation experiments sociobiology systematics universal darwinism social implications eugenics evolution as fact and theory dysgenics social effects creation evolution controversy theistic evolution objections to evolution level of support nature nurture controversy evolutionary biology portal category v t e mutation and selection a belgian blue cow the defect in the breed s myostatin gene is maintained through linebreeding and is responsible for its accelerated lean muscle growth this chihuahua mix and great dane shows the wide range of dog breed sizes created using selective breeding selective breeding transformed teosinte s few fruitcases left into modern maize s rows of exposed kernels right selective breeding also called artificial selection is the process by which humans use animal breeding and plant breeding to selectively develop particular phenotypic traits characteristics by choosing which typically animal or plant males and females will sexually reproduce and have offspring together domesticated animals are known as breeds normally bred by a professional breeder while domesticated plants are known as varieties cultigens cultivars or breeds 1 two purebred animals of different breeds produce a crossbreed and crossbred plants are called hybrids flowers vegetables and fruit trees may be bred by amateurs and commercial or non commercial professionals major crops are usually the provenance of the professionals in animal breeding artificial selection is often combined with techniques such as inbreeding linebreeding and outcrossing in plant breeding similar methods are used charles darwin discussed how selective breeding had been successful in producing change over time in his 1859 book on the origin of species its first chapter discusses selective breeding and domestication of such animals as pigeons cats cattle and dogs darwin used artificial selection as an analogy to propose and explain the theory of natural selection but distinguished the latter from the former as a separate process that is non directed 2 3 4 the deliberate exploitation of selective breeding to produce desired results has become very common in agriculture and experimental biology selective breeding can be unintentional for example resulting from the process of human cultivation and it may also produce unintended desirable or undesirable results for example in some grains an increase in seed size may have resulted from certain ploughing practices rather than from the intentional selection of larger seeds most likely there has been an interdependence between natural and artificial factors that have resulted in plant domestication 5 history edit selective breeding of both plants and animals has been practiced since prehistory key species such as wheat rice and dogs have been significantly different from their wild ancestors for millennia and maize which required especially large changes from teosinte its wild form was selectively bred in mesoamerica selective breeding was practiced by the romans 6 treatises as much as 2 000 years old give advice on selecting animals for different purposes and these ancient works cite still older authorities such as mago the carthaginian 7 the notion of selective breeding was later expressed by the polymath abu rayhan biruni in the 11th century he noted the idea in his book titled india which included various examples 8 the agriculturist selects his corn letting grow as much as he requires and tearing out the remainder the forester leaves those branches which he perceives to be excellent whilst he cuts away all others the bees kill those of their kind who only eat but do not work in their beehive abu rayhan biruni india selective breeding was established as a scientific practice by robert bakewell during the british agricultural revolution in the 18th century arguably his most important breeding program was with sheep using native stock he was able to quickly select for large yet fine boned sheep with long lustrous wool the lincoln longwool was improved by bakewell and in turn the lincoln was used to develop the subsequent breed named the new or dishley leicester it was hornless and had a square meaty body with straight top lines 9 these sheep were exported widely including to australia and north america and have contributed to numerous modern breeds despite the fact that they fell quickly out of favor as market preferences in meat and textiles changed bloodlines of these original new leicesters survive today as the english leicester or leicester longwool which is primarily kept for wool production bakewell was also the first to breed cattle to be used primarily for beef previously cattle were first and foremost kept for pulling ploughs as oxen 10 but he crossed long horned heifers and a westmoreland bull to eventually create the dishley longhorn as more and more farmers followed his lead farm animals increased dramatically in size and quality in 1700 the average weight of a bull sold for slaughter was 370 pounds 168 kg by 1786 that weight had more than doubled to 840 pounds 381 kg however after his death the dishley longhorn was replaced with short horn versions he also bred the improved black cart horse which later became the shire horse charles darwin coined the term selective breeding he was interested in the process as an illustration of his proposed wider process of natural selection darwin noted that many domesticated animals and plants had special properties that were developed by intentional animal and plant breeding from individuals that showed desirable characteristics and discouraging the breeding of individuals with less desirable characteristics darwin used the term artificial selection twice in the 1859 first edition of his work on the origin of species in chapter iv natural selection and in chapter vi difficulties on theory slow though the process of selection may be if feeble man can do much by his powers of artificial selection i can see no limit to the amount of change to the beauty and infinite complexity of the co adaptations between all organic beings one with another and with their physical conditions of life which may be effected in the long course of time by nature s power of selection 11 charles darwin on the origin of species we are profoundly ignorant of the causes producing slight and unimportant variations and we are immediately made conscious of this by reflecting on the differences in the breeds of our domesticated animals in different countries more especially in the less civilized countries where there has been but little artificial selection 12 charles darwin on the origin of species animal breeding edit main article animal breeding animals with homogeneous appearance behavior and other characteristics are known as particular breeds or pure breeds and they are bred through culling animals with particular traits and selecting for further breeding those with other traits purebred animals belong to a single recognizable breed and purebreds with recorded lineage are called pedigreed crossbreeds are a mix of two purebreds whereas mixed breeds are a mix of several breeds often unknown animal breeding begins with breeding stock a group of animals used for the purpose of planned breeding when individuals are looking to breed animals they look for certain valuable traits in purebred stock for a certain purpose or may intend to use some type of crossbreeding to produce a new type of stock with different and presumably superior abilities in a given area of endeavor for example to breed chickens a breeder typically intends to receive eggs meat and new young birds for further reproduction thus the breeder has to study different breeds and types of chickens and analyze what can be expected from a certain set of characteristics before he or she starts breeding them therefore when purchasing initial breeding stock the breeder seeks a group of birds that will most closely fit the purpose intended purebred breeding aims to establish and maintain stable traits that animals will pass to the next generation by breeding the best to the best employing a certain degree of inbreeding considerable culling and selection for superior qualities one could develop a bloodline superior in certain respects to the original base stock such animals can be recorded with a breed registry the organization that maintains pedigrees and or stud books however single trait breeding breeding for only one trait over all others can be problematic 13 in one case mentioned by the animal behaviorist temple grandin roosters bred for fast growth or heavy muscles did not know how to perform typical rooster courtship dances which alienated the roosters from hens and led the roosters to kill the hens after mating with them 13 a soviet attempt to breed lab rats with higher intelligence led to cases of neurosis severe enough to make the animals incapable of any problem solving unless drugs like phenazepam were used 14 the observable phenomenon of hybrid vigor stands in contrast to the notion of breed purity however on the other hand indiscriminate breeding of crossbred or hybrid animals may also result in degradation of quality studies in evolutionary physiology behavioral genetics and other areas of organismal biology have also made use of deliberate selective breeding though longer generation times and greater difficulty in breeding can make these projects challenging in such vertebrates as house mice 15 16 17 plant breeding edit main article plant breeding researchers at the usda have selectively bred carrots with a variety of colors the process of plant breeding has been used for thousands of years and began with the domestication of wild plants into uniform and predictable agricultural cultigens these high yielding varieties have been particularly important in agriculture as crops improved humans were able to move from hunter gatherer style living to a mix of hunter gatherer and agriculture practices 18 although these higher yielding plants were derived from an extremely primitive version of plant breeding this form of agriculture was an investment that the people who grew them were planting then could have a more varied diet this meant that they did not completely stop their hunting and gathering immediately but instead over time transitioned and ultimately favored agriculture 19 originally this was due to humans not wanting to risk using all their time and resources for their crops just to fail which was promptly called play farming due to the idea of farmers experimenting with agriculture 19 in addition the ability for humans to stay within one place for food and create permanent settlements made the process move along faster 20 during this transitional period crops began to acclimate and evolve with humans encouraging humans to invest further into crops over time this reliance on plant breeding has created problems as highlighted by the book botany of desire where michael pollan shows the connection between basic human desires through four different plants apples for sweetness tulips for beauty cannabis for intoxication and potatoes for control in a form of coevolution humans have influenced these plants as much as the plants have influenced the people that consume them 21 selective plant breeding is also used in research to produce transgenic animals that breed true i e are homozygous for artificially inserted or deleted genes 22 selective breeding in aquaculture edit selective breeding in aquaculture holds high potential for the genetic improvement of fish and shellfish for the process of production unlike terrestrial livestock the potential benefits of selective breeding in aquaculture were not realized until recently this is because high mortality led to the selection of only a few broodstock causing inbreeding depression which then forced the use of wild broodstock this was evident in selective breeding programs for growth rate which resulted in slow growth and high mortality 23 control of the reproduction cycle was one of the main reasons as it is a requisite for selective breeding programs artificial reproduction was not achieved because of the difficulties in hatching or feeding some farmed species such as eel and yellowtail farming 24 a suspected reason associated with the late realization of success in selective breeding programs in aquaculture was the education of the concerned people researchers advisory personnel and fish farmers the education of fish biologists paid less attention to quantitative genetics and breeding plans 25 another was the failure of documentation of the genetic gains in successive generations this in turn led to failure in quantifying economic benefits that successful selective breeding programs produce documentation of the genetic changes was considered important as they help in fine tuning further selection schemes 23 quality traits in aquaculture edit aquaculture species are reared for particular traits such as growth rate survival rate meat quality resistance to diseases age at sexual maturation fecundity shell traits like shell size shell color etc growth rate growth rate is normally measured as either body weight or body length this trait is of great economic importance for all aquaculture species as faster growth rate speeds up the turnover of production 25 improved growth rates show that farmed animals utilize their feed more efficiently through a positive correlated response 24 survival rate survival rate may take into account the degrees of resistance to diseases 24 this may also see the stress response as fish under stress are highly vulnerable to diseases 25 the stress fish experience could be of 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