Illustration from The Descent of Man and Selection in Relation to Sex by Charles Darwin showing the Tufted Coquette Lophornis ornatus, female on left, ornamented male on right. The Descent of Man and Selection in Relation to Sex is a book on Evolutionary theory by English naturalist Charles Darwin, first Charles Robert Darwin (February 12 1809 &ndash April 19 1882 was an English naturalist, who realised and demonstrated that all Species of life The Tufted Coquette ( Lophornis ornatus) is a tiny Hummingbird that breeds in eastern Venezuela, Trinidad, Guiana and northern

Sexual selection is the theory proposed by Charles Darwin that states that certain evolutionary traits can be explained by competition between members of a species. The word theory has many distinct meanings in different fields of Knowledge, depending on their methodologies and the context of discussion. Charles Robert Darwin (February 12 1809 &ndash April 19 1882 was an English naturalist, who realised and demonstrated that all Species of life Darwin defined sexual selection as the effects of the "struggle between the individuals of one sex, generally the males, for the possession of the other sex". ^[1] Biologists today distinguish between "male to male combat" (it is usually males who fight each other), "mate choice" (usually female choice of male mates) and sexual conflict. Foundations of modern biology There are five unifying principles Sexual conflict occurs when the two Sexes have conflicting optimal fitness strategies concerning Reproduction, leading to Evolutionary arms race Traits selected for by male combat are called secondary sexual characteristics (including: horns, antlers, etc. ) and sometimes referred to as "weapons", and traits selected by mate choice are called "ornaments". Much attention has recently been given to cryptic female choice,^[2] a phenomenon in internally fertilising animals such as mammals and birds, where a female will get rid of a male's sperm without his knowledge. The term sperm is derived from the Greek word (σπέρμα sperma (meaning "seed" and refers to the male reproductive cells. The equivalent in male-to-male combat is sperm competition. Sperm competition is " competition between Sperm of two or more Males for the Fertilization of an Ovum " (Parker 1970

Male to male combat is also classified as intrasexual competition, while mate choice and mate coercion are also known as intersexual competition.

Females often prefer to mate with males with external ornaments - exaggerated features of morphology. These can plausibly arise because an arbitrary female preference for some aspect of male morphology initially increased by genetic drift, creating, in due course, selection for males with the appropriate ornament. In Population genetics, genetic drift is the accumulation of random events that change the makeup of a gene pool slightly but often compound over time This is known as the sexy son hypothesis. The sexy son hypothesis is a concept from Evolutionary biology, proposed by P Alternatively, genes that enable males to develop great ornaments may simply show off greater disease resistance or a more efficient metabolism - features that also benefit females. An immune system is a collection of mechanisms within an Organism that protects against Disease by identifying and killing Pathogens and Tumor Metabolism is the set of Chemical reactions that occur in living Organisms in order to maintain Life. This idea is known as the good genes hypothesis. Sexual selection is the Theory proposed by Charles Darwin that states that certain evolutionary traits can be explained by Intraspecific competition

Phylogeny of sexual selection and base conditions

The success of an organism is not only measured by the number of offspring left behind, but by the quality or probable success of the offspring: reproductive fitness. Reproductive success is defined as the passing of Genes onto the next Generation in a way that they too can pass those genes on Sexual selection is the expansion on the ability of organisms to differentiate each other at the species level, interspecies selection.

The expansion of interspecies selection and intraspecies selection is a driving force behind species fission: the separation of a single contiguous species into multiple non-contiguous variants. Sir Ronald Aylmer Fisher, FRS ( 17 February 1890 – 29 July 1962) was an English Statistician, Evolutionary Sexual preference creates a specialized tendency towards homogamy that provides a system by which a group constantly invaded by the diffusion of unfavourable genes may suppress ill effects.

When it is possible for it to be exercised usefully, the general conditions of sexual discrimination appear to be (1) the acceptance of one mate precludes the effective acceptance of alternative mates, and (2) the rejection of an offer will be followed by other offers, either certainly, or at such high chance that the risk of non-occurrence will be smaller than the chance advantage to be gained by selecting a mate. Sir Ronald Aylmer Fisher, FRS ( 17 February 1890 – 29 July 1962) was an English Statistician, Evolutionary

Intrasexual and intersexual selection

Male Northern Elephant Seals fight fiercely each year. The Northern Elephant Seal ( Mirounga angustirostris) is one of two Species of Elephant seal (the other is the Southern Elephant Seal) Unsuccessful males will not mate at all, while successful males have harems of 30 to 100 females.

Sexual selection takes two major forms: intrasexual selection (also known as 'male–male competition') in which members of the less limited sex (typically males) compete aggressively among themselves for access to the limiting sex, and intersexual selection (also known as 'mate choice' or 'female choice') in which males compete with each other to be chosen by females.

With intrasexual selection it should be brought to mind that adorned males will gain reproductive advantage without the intervention of female preference and intersexual selection. Charles Robert Darwin (February 12 1809 &ndash April 19 1882 was an English naturalist, who realised and demonstrated that all Species of life This advantage will be conferred by weapons used in the process of resolving disputes, such as those over territorial rights. The use of male sexual ornamentation is primarily used in the search of asymmetries between rival males, contrary to what would seem most obvious (mortally wounding the opponent), since a high number of fatal combats over territory would result in a clear disadvantage. The use of sexual ornamentation is used as a signaling device (signalling theory) amongst males to create a dominance hierarchy, also known as a pecking order, without unneeded detriment and fatality. Within Evolutionary biology, signalling theory refers to a body of theoretical work examining communication between individuals A dominance hierarchy (in humans Social hierarchy) is the organization of individuals in a group that occurs when competition of resources lead to aggression Pecking Order is a Card game, where players try to claim the best feeding spots in the jungle by playing their birds on the perches and determining who's stronger It is predominantly when two opposing males are so closely matched, as would be found in males not having established themselves in a dominance hierarchy, that asymmetries cannot be found and the confrontation escalates to a point where the asymmetries must be proved by aggressive use of ornamentation.

How often males will physically engage each other, and in what manner, can best be understood by applying game theory developed for biology, most notably by John Maynard Smith^[3]. Sir Ronald Aylmer Fisher, FRS ( 17 February 1890 – 29 July 1962) was an English Statistician, Evolutionary Game theory is a branch of Applied mathematics that is used in the Social sciences (most notably Economics) Biology, Engineering, Maynard Smith redirects here -- for other uses see Maynard Smith (disambiguation Professor John Maynard Smith, F

In addition to conventional aggression, male–male competition may take the form of sperm competition. Sperm competition is " competition between Sperm of two or more Males for the Fertilization of an Ovum " (Parker 1970

However, 'sexual selection' typically refers to the process of choice (the limiting factor, which is typically females) over members of the opposite sex (the non-limited factor, typically males). This process is known as intersexual selection. Fisher pointed out that preference could be under genetic control and therefore subject to a combination of natural and sexual selection just as much as the qualities of the ornamentation 'preferred'.

An example of intersexual selection: the female peahen chose to mate with the male peacock who had the most beautiful plumage in her mind. The term peafowl refers to Gallinaceous Birds classified within the genera Rheinardia Argusianus Afropavoand Pavo The term peafowl refers to Gallinaceous Birds classified within the genera Rheinardia Argusianus Afropavoand Pavo

The conditions determining which sex is the limiting factor in intersexual selection can be best understood by way of Bateman's principle which states that the sex which invests the most in producing offspring becomes a limiting resource over which the other sex will compete. In Biology, Bateman's principle is the theory that females almost always invest more Energy into producing Offspring than males and therefore in most species This can be most easily illustrated by the contrast in nutritional investment into a zygote between egg and sperm, and the limited reproductive capacity of females compared to males. For other meanings see Zygote (disambiguation. A zygote (from Greek ζυγωτός zugōtos "joined" or "yoked"

Geometric progression

In species which the reproductive success of one sex depends heavily on winning the concession of the other, as is evident with many polygamous birds, sexual selection will act by increasing the degree of preference to which it is due, with the consequence that both the trait preferred and the intensity of preference will be increased together with ever-increasing velocity. This process causing a fervent and rapid evolution of both the conspicuous ornamentation and the preference for such, until so arrested directly or indirectly by bionomic Natural Selection reasons. Thus, in many cases a positive feedback loop of sexual selection is created, resulting with exorbitant physical structures in the non-limited sex, the most notorious example being the peacock (shown above). The term peafowl refers to Gallinaceous Birds classified within the genera Rheinardia Argusianus Afropavoand Pavo It is important to note that while a peacock may have exorbitant plumage, the peahen has even more exorbitant taste for such.

Initially to start the process, there would be a correlation between the trait and higher fitness. Two previously isolated species, A and B, could come to inhabit the same area resulting in some hybridization. In this situation reproductive isolation will be favored. If the mean value of a trait e. g. tails, in species A, is larger than those of species B, selection would favor females of species A with preference for large tails. Once started the process could continue past the need for species isolation.

The peahen will desire to copulate with the most attractive Peacock so that her progeny, if male, will be attractive to females in the next generation. The term peafowl refers to Gallinaceous Birds classified within the genera Rheinardia Argusianus Afropavoand Pavo Additionally the Peacock will desire to copulate with a Peahen that finds him attractive so that if the progeny is female, preference for his degree of ornamentation remains present in the next generation. Since the rate of change in preference is proportioned according to the highest average degree of taste amongst females, and that females desire to best other members of the sex, it creates an additive effect in the cyclical process that will yield exponential increases, in both sexes, if unchecked.

R. A. Fisher in The Genetical Theory of Natural Selection was the first to articulate this process in a game theoretic style treatment. The Genetical Theory of Natural Selection is a book by RA Fisher.

Since R. Sir Ronald Aylmer Fisher, FRS ( 17 February 1890 – 29 July 1962) was an English Statistician, Evolutionary A. Fishers initial conceptual model of the 'run-away' process, various others have continued the work on modeling an accurate mathematical proof. Notably R. Lande^[5] & P. O'Donald.

Sexual dimorphism

The Rhinoceros beetle demonstrates a classic case of sexual dimorphism. ---- The rhinoceros beetles or rhino beetle are a subfamily ( Dynastinae) of Beetles in the family of Scarab beetles (Scarabaeidae This plate is from Darwin's Descent of Man, with the male at top, female at bottom. The Descent of Man and Selection in Relation to Sex is a book on Evolutionary theory by English naturalist Charles Darwin, first

Sex differences directly related to reproduction and serving no direct purpose in courtship are called primary sexual characteristics. A sex organ, or primary sexual characteristic, as narrowly defined is any of the anatomical parts of the body which are involved in sexual reproduction and constitute Traits amenable to sexual selection, which give an organism an advantage over its rivals (such as in courtship) without being directly involved in reproduction, are called secondary sex characteristics. Reproduction is the Biological process by which new individual Organisms are produced Secondary sex characteristics are traits that distinguish the two Sexes of a species but that are not directly part of the Reproductive system.

In most sexual species the males and females have different equilibrium strategies, due to a difference in relative investment in producing offspring. Male (♂ refers to the sex of an organism or part of an organism which produces small mobile Gametes called spermatozoa. Female (♀ is the Sex of an Organism, or a part of an organism which produces ova (egg cells In Game theory, the Nash equilibrium (named after John Forbes Nash, who proposed it is a Solution concept of a game involving two or more players in which As formulated in Bateman's principle, females have a greater initial investment in producing offspring (pregnancy in mammals or the production of the egg in birds and reptiles) , and this difference in initial investment creates differences in variance in expected reproductive success and bootstraps the sexual selection processes. Pregnancy ( Latin graviditas) is the carrying of one or more offspring known as a Fetus or Embryo, inside the Uterus of a Female Birds ( class Aves) are bipedal endothermic ( Warm-blooded) Vertebrate animals that lay eggs. Reptiles, or members of the class Reptilia are air-breathing Cold-blooded Vertebrates that have skin covered in scales as opposed to hair or feathers Classic examples of reversed sex-role species include the pipefish, and Wilson's phalarope. Pipefishes or pipe-fishes ( Syngnathinae) are a subfamily of small Fishes which with the Seahorses form a distinct family Also, unlike a female, a male (except in monogamous species) has some uncertainty about whether or not he is the true parent of a child, and so will be less interested in spending his energy helping to raise offspring that may or may not be related to him. Monogamy is the custom or condition of having only one mate in a Relationship, thus forming a Couple. As a result of these factors, males are typically more willing to mate than females, and so females are typically the ones doing the choosing (except in cases of forced copulations, which can occur in certain species of primates, ducks, and others). Sexual conflict occurs when the two Sexes have conflicting optimal fitness strategies concerning Reproduction, leading to Evolutionary arms race A primate is a member of the biological order Primates ( Latin: "prime first rank" the group that contains Lemurs the Aye-aye For duck as a food see Duck (food; for other meanings see Duck (disambiguation. The effects of sexual selection are thus held to typically be more pronounced in males than in females.

Differences in secondary sexual characteristics between males and females of a species are referred to as sexual dimorphisms. Sexual dimorphism is the systematic difference in form between individuals of different Sex in the same Species. These can be as subtle as a size difference (sexual size dimorphism, often abbreviated as SSD) or as extreme as horns and color patterns. Sexual dimorphisms abound in nature. Examples include the possession of antlers by only male deer, and the brighter coloration of many male birds, in comparison with females of the same species. The peacock, with its elaborate and colorful tail feathers, which the peahen lacks, is often referred to as perhaps the most extraordinary example of a dimorphism. The term peafowl refers to Gallinaceous Birds classified within the genera Rheinardia Argusianus Afropavoand Pavo The term peafowl refers to Gallinaceous Birds classified within the genera Rheinardia Argusianus Afropavoand Pavo The largest sexual size dimorphism in vertebrates is the shell dwelling cichlid fish Neolamprologus callipterus in which males are up to 30 times the size of females. Vertebrates are members of the Subphylum Vertebrata, Chordates with backbones or spinal columns The grouping sometimes includes The terms shell dwellers or shelldwellers, shell-breeding, or ostracophil are descriptive terms for Cichlid Fish that use the empty Cichlids (ˈsɪklɪd are Fish from the family Cichlidae in the order Perciformes. Fish are aquatic Vertebrate animals that are typically ectothermic (previously Cold-blooded) covered with scales, and equipped with two Extreme sexual size dimorphism, with females larger than males, is quite common in spiders. Spiders are Predatory Invertebrate Animals that have two body segments, eight legs no chewing mouth parts and no wings

Viability and variations of the theory

Due to their sometimes greatly exaggerated nature, secondary sexual characteristics can prove to be a hindrance to an animal, thereby lowering its fitness. Fitness (often denoted w in Population genetics models is a central concept in evolutionary theory. For example, the large antlers of a moose are bulky and heavy and slow the creature's flight from predators; they also can become entangled in low-hanging tree branches and shrubs, and undoubtedly have led to the demise of many individuals. Bright colorations and showy ornamenations, such as those seen in many male birds, in addition to capturing the eyes of females, also attract the attention of predators; when a male peacock spreads its tail, it is beautiful, but very obvious (though this may actually be advantageous to the survival of the male's offspring and the breeding population as a whole; see below). Some of these traits also represent energetically costly investments for the animals that bear them. Because traits held to be due to sexual selection often conflict with the survival fitness of the individual, the question then arises as to why, in nature, in which survival of the fittest is considered the rule of thumb, such apparent liabilities are allowed to persist. "Survival of the fittest" is a Phrase which is shorthand for a concept relating to competition for survival or predominance

An often-cited theory published by R.A. Fisher in 1930 that attempts to resolve the paradox posits that such traits are the results of explosive positive feedback loops that have as their starting points particular sexual preferences for features that confer a survival advantage and thus "become established in the species. Sir Ronald Aylmer Fisher, FRS ( 17 February 1890 – 29 July 1962) was an English Statistician, Evolutionary Year 1930 ( MCMXXX) was a Common year starting on Wednesday (link will display 1930 calendar of the Gregorian calendar. Positive feedback, sometimes referred to as "cumulative causation" is a Feedback loop system in which the system responds to perturbation in the same direction " Fisher argued that such features advance in the direction of the preference even beyond the optimal level for survival, until the selection pressure of female choice is precisely counterbalanced by the resultant disadvantage for survival. Fisher further argued that the strength of the female preference tends to grow exponentially (leading to 'explosive' evolution of the characteristic) until finally checked by ecological selection, since the offspring of those females with the strongest preference typically fare better in reproducing than the offspring of females with weaker preferences. Any mutations for the preference opposite to the given characteristic, though tending to promote survival against ecological selection, nevertheless tend not to survive in the gene pool because male offspring that result from matings based on the preference are less sexually attractive to the majority of the females in the population, and thus infrequently chosen as mates. In Population genetics, a gene pool is the complete set of unique Alleles in a Species or Population. In Biology, mating is the pairing of opposite- Sex or hermaphroditic Organisms for copulation and in Social animals also to raise their An equivalent way of expressing this is that if most females are looking, for example, for long-tailed males, then each female individually does better to select a long-tailed male, since then her male children are more likely to succeed. (The females do not actually have this thought process; this kind of "decision" is an evolutionarily stable strategy. In Game theory and Behavioural ecology, an evolutionarily stable strategy (ESS is a strategy which if adopted by a population of players )

Other theories highlight intrinsically useful qualities of such traits. Antlers, horns and the like can be used in physical defense from a predator, and also in show jousting or competition among males in a species. Competition is a rivalry between individuals groups nations or animals for territory or resources The winner, who typically becomes the dominant animal in the population, is granted access to females, and therefore increases his reproductive output. Antlers are not the only mechanism that can be used to counteract predation. Predators typically look for the eyes of their prey so they can attack that end of the creature. The conspicuousness of eyespots on many species of butterflies and fishes confuses predators and helps to prevent the prey from suffering serious damage. [1]

Another, more recently developed, theory, the Handicap principle of Amotz Zahavi, Russell Lande and W. D. Hamilton, holds that the fact that the male of the species is able to survive until and through the age of reproduction with such a seemingly maladaptive trait is effectively considered by the female to be a testament to his overall fitness. The handicap principle is a Hypothesis originally proposed in 1975 by biologist Amotz Zahavi to explain how Evolution may lead to Amotz Zahavi ( Hebrew: אמוץ זהבי) (born 1928 is an Israeli evolutionary biologist, a Professor Emeritus at the Zoology William Donald Hamilton, FRS ( 1 August 1936 &mdash 7 March 2000) was a British Evolutionary biologist Such handicaps might prove he is either free of or resistant to disease, or it might demonstrate that this animal possesses more speed or a greater physical strength that is used to combat the troubles brought on by the exaggerated trait. A disease is an abnormal condition of an organism that impairs bodily functions and can be deadly

Zahavi's work spurred a re-examination of the field, which has produced an ever-accelerating number of theories. In 1984, Hamilton and Marlene Zuk introduced the "Bright Male" hypothesis, suggesting that male elaborations might serve as a marker of health, by exaggerating the effects of disease and deficiency. In 1990, Michael Ryan and A. S. Rand, working with the túngara frog, proposed the hypothesis of "Sensory Exploitation", where exaggerated male traits may provide a sensory stimulation that females find hard to resist. In 1991, Anders Pape Møller, working with the tails of male barn swallows, introduced fluctuating asymmetry to the field. Symmetry, especially facial symmetry, is one of a number of Aesthetic traits including Averageness and Youthfulness, associated with Health Fluctuating asymmetry, a concept previously invoked under natural selection, is based on the observations that healthier specimens have more left-to-right sided symmetry than less healthy specimens. Subsequently the theories of the "Gravity Hypothesis" by Jordi Moya-Larano et al. and "Chase Away" by Brett Holland and William R. Rice have also been added. In addition, in the late 1970s Janzen and Mary Willson, noting that male flowers are often larger than female flowers, expanded the field of sexual selection into plants. Plants are living Organisms belonging to the kingdom Plantae.

In the past few years, the field has exploded to include many additional areas of study, not all of which are clearly included under Darwin's definition of sexual selection. These include cuckoldry, nuptial gifts, sperm competition, infanticide, physical beauty, mating by subterfuge, species isolation mechanisms, male parental care, ambiparental care, mate location, polygamy, and mechanisms that can only be called bizarre, including homosexual rape in certain male animals, cementing of females' vaginal pores by males in some lepidopteran insects, and insect penises specialized to remove any sperm packets from females which may have been deposited by previous suitors. A cuckold is a married man whose wife has sex with other men In current usage it sometimes refers to non-married couples in committed relationships as well although the traditional meaning Sperm competition is " competition between Sperm of two or more Males for the Fertilization of an Ovum " (Parker 1970 Infanticide is the practice of someone intentionally causing the death of an Infant.

Focusing on the effect of sexual conflict, as hypothezised by William Rice, Locke Rowe et Göran Arnvist^[6], Thierry Lodé^[7] underlines that the divergence of interest constitutes a key for evolutionary process. Sexual conflict occurs when the two Sexes have conflicting optimal fitness strategies concerning Reproduction, leading to Evolutionary arms race Born in 1956 Thierry Lodé is a French biologist professor teaching Evolutionary ecology in the CNRS Units ETHOS (Ethology Evolution Ecology of Rennes1, France Sexual conflict leads to an antagonistic co-evolution in which one sex tends to control the other, resulting in a tug of war. In Evolutionary biology, an evolutionary arms race is an Evolutionary struggle between competing sets of co-evolving Genes that develop adaptations

These theories are not mutually exclusive; combinations of them may also be considered.

Noting, however, that this proliferation of theories and the widening confusion about the definition of the field matches the patterns of a Kuhnian crisis, Joe Abraham published two papers questioning whether the problems of sexual selection might be explained under natural selection. Paradigm shift, sometimes known as extraordinary science or revolutionary science, is the term first used by Thomas Kuhn in his influential In 1998, he published the Female Sabotage hypothesis, pointing out that mating provides females with the opportunity to sabotage polygamous males, by only mating with males who exhibit life-threatening traits. Female sabotage is an Evolutionary theory regarding the propensity of certain females to select "burdened" males of their species for mating As males increasingly die as a result of their elaborations, fighting, and mating exertions, their declining numbers leave more food and other resources for females and offspring, and relieve them of predation pressure. As females are the limiting resource in most species, as their numbers increase, population fitness also increases.

In 2005 Abraham published a companion paper looking at sexual dimorphism in flower sizes, resurrecting an older theory by Hermann Müller, that larger male flowers may simply serve to attract pollinators to pollen donors before they visit pollen acceptors. For other Hermann Müllers see Hermann Müller. Heinrich Ludwig Hermann Müller (1829-1883 German botanist who provided important Abraham's experimental data showed strongly that this is the case, and flower dimorphisms may also be a function under natural selection rather than sexual selection. Natural selection is the process by which favorable Heritable traits become more common in successive Generations of a Population of

In humans

Charles Darwin conjectured that the male beard, as well as the relative hairlessness of humans compared to nearly all other mammals, are results of sexual selection. He reasoned that since, compared to males, the bodies of females are more nearly hairless, hairlessness is one of the atypical cases due to its selection by males at a remote prehistoric time, when males had overwhelming selective power, and that it nonetheless affected males due to genetic correlation between the sexes. He also hypothesized that sexual selection could also be what had differentiated between different human races, as he did not believe that natural selection provided a satisfactory answer. The term race or racial group usually refers to the concept of categorizing Humans into Populations or groups on the basis of various sets

Geoffrey Miller, drawing on some of Darwin's largely neglected ideas about human behavior, has hypothesized that many human behaviors not clearly tied to survival benefits, such as humor, music, visual art, verbal creativity, and some forms of altruism, are courtship adaptations that have been favored through sexual selection. Geoffrey Miller (born 1965 is an American Evolutionary psychologist; his work is in the tradition of Richard Dawkins, Daniel Dennett, and Steven Pinker In that view, many human artefacts could be considered subject to sexual selection as part of the extended phenotype, for instance clothing that enhance sexually selected traits. The Extended Phenotype (subtitled "The Gene as the Unit of Selection" and later "The Long Reach of the Gene" is a 1982 book by Richard

Some hypotheses about the evolution of the human brain argue that it is a sexually selected trait, as it would not confer enough fitness in itself relative to its high maintenance costs (a quarter to a fifth of the energy and oxygen consumed by a human). ^[8]

The zoologist Richard Dawkins pointed out in 1989 that the loss of the penis bone in humans, when it is present in our nearest related species the chimpanzee, demands some form of evolutionary explanation. Clinton Richard Dawkins, FRS, FRSL (born 26 March 1941 is a British ethologist, evolutionary biologist, and Popular science The baculum (also penis bone, penile bone or os penis) is a Bone found in the Penis of most Mammals It is absent Chimpanzee (often shortened to chimp) is the common name for the two extant Species of Apes in the Genus Pan. He speculates that its loss is probably a form of sexual selection by females looking for signs of good health in prospective mates. The reliance of the human penis solely on hydraulic means to achieve a rigid state makes it particularly vulnerable to blood pressure variation. For the mechanical technology see Hydraulic machinery and Hydraulic cylinder Hydraulics is a topic of science and Engineering Poor erectile function betrays, not only physical states such as diabetes and neurological disorders, but mental states such as stress and depression. ^[9]

History and application of the theory

Victorian cartoonists quickly picked up on Darwin's ideas about the role of display in sexual selection. Here Darwin is fascinated by the apparent steatopygia in the new fashion for bustles. Steatopygia (stiˌætəˈpɪdʒiə is a high degree of Fat accumulation in and around the Buttocks The deposit of fat is not confined to the Gluteal regions A bustle is a type of framework used to expand the fullness or support the drapery of the back of a woman's dress occurring predominantly between the mid- to late 1800s The woman asks him to "leave my emotions alone", a reference to Darwin's new book The Expression of the Emotions in Man and Animals. The Expression of the Emotions in Man and Animals is a book by the British naturalist Charles Darwin published in 1872, on how Humans

The theory of sexual selection was first proposed by Charles Darwin in his book The Origin of Species, though it was primarily devoted to natural selection. Charles Darwin 's On the Origin of Species (published 24 November 1859) is a seminal work in Scientific literature and arguably the A later work, The Descent of Man and Selection in Relation to Sex dealt with the subject of sexual selection exhaustively, in part because Darwin felt that natural selection alone was unable to account for certain types of apparently non-competitive adaptations, such as the tail of a male peacock. The Descent of Man and Selection in Relation to Sex is a book on Evolutionary theory by English naturalist Charles Darwin, first The term peafowl refers to Gallinaceous Birds classified within the genera Rheinardia Argusianus Afropavoand Pavo He once wrote to a colleague that "The sight of a feather in a peacock's tail, whenever I gaze at it, makes me sick!" His work divided sexual selection into two primary categories: male-male competition (which would produce adaptations such as a Bighorn Sheep's horns, which are used primarily in sparring with other males over females), and cases of female choice (which would produce adaptations like beautiful plumage, elaborate songs, and other things related to impressing and attracting). Bighorn Sheep ( Ovis canadensis) is a species of sheep in North America and Siberia with large horns which can weigh up to.

Darwin's views on sexual selection were opposed strongly by his "co-discoverer" of natural selection, Alfred Russel Wallace, though much of his "debate" with Darwin took place after Darwin's death. Alfred Russel Wallace OM, FRS (8 January 1823 &ndash 7 November 1913 was an British naturalist, Explorer, Geographer Wallace argued that the aspects of it which were male-male competition, while real, were simply forms of natural selection, and that the notion of "female choice" was attributing the ability to judge standards of beauty to animals far too cognitively undeveloped to be capable of aesthetic feeling (such as beetles). Beetles are the group of Insects with the largest number of known Species.

Wallace also argued that Darwin too much favored the bright colors of the male peacock as adaptive without realizing that the "drab" peahen's coloration is itself adaptive, as camouflage. The term peafowl refers to Gallinaceous Birds classified within the genera Rheinardia Argusianus Afropavoand Pavo Camouflage is a method of cryptic or concealing coloration that allows an otherwise visible Organism Wallace more speculatively argued that the bright colors and long tails of the peacock were not adaptive in any way, and that bright coloration could result from non-adaptive physiological development (for example, the internal organs of animals, not being subject to a visual form of natural selection, come in a wide variety of bright colors). This has been questioned by later scholars as quite a stretch for Wallace, who in this particular instance abandoned his normally strict "adaptationist" agenda in asserting that the highly intricate and developed forms such as a peacock's tail resulted by sheer "physiological processes" that were somehow not at all subjected to adaptation. Adaptationism is a set of methods in the evolutionary sciences for distinguishing the products of adaptation from traits that arise through other processes

Though Darwin considered sexual and natural selection to be two separate processes of equal importance, most of his contemporaries were not convinced, and sexual selection is usually de-emphasized as being a lesser force than, or simply a part of, natural selection.

The sciences of evolutionary psychology, human behavioral ecology, and sociobiology study the influence of sexual selection in humans, though these are often controversial fields. Evolutionary psychology ( EP) attempts to explain mental and psychological traits ��such as Memory, Perception, Human behavioral ecology (HBE or human evolutionary ecology applies the principles of Evolutionary theory and optimization to the study of Human Sociobiology is a neo-Darwinian and Socialism Synthesis of Scientific disciplines that attempts to explain Social behavior The field of epigenetics is broadly concerned with the competence of adult organisms within a given sexual, social, and ecological niche, which includes the development of mating competences, e. In Biology, the term epigenetics refers to changes in Gene expression caused by mechanisms other than changes in the underlying DNA sequence g. , by mimicking adult behavior.

Criticism

A group of authors led by Joan Roughgarden have criticised sexual selection theory,^[10] claiming there was evidence that individuals did not compete strongly for mating opportunities, but that the function of sex was mostly social. Joan E Roughgarden (b Jonathan Roughgarden in Paterson New Jersey on 13 March 1946) is an American Biologist. The evidence used in the paper, however, was heavily criticised by many other notable authors for its factual inaccuracy. ^[11] Cultural critics have noted that Darwin's ideas about sexual selection were strongly shaped by Victorian mores and at times reflect a distinct chauvinistic bias. ^[12]

See also

Notes

1. ^ Darwin, C. In Psychology and other social and Behavioral sciences aggression refers to behavior that is intended to cause harm Assortative mating (also called assortative pairing) takes place when sexually reproducing Organisms tend to Mate with individuals that are like NOTICE TO WOULD-BE-ROMEOS*************** Competition can be defined as an interaction between Organisms or Species, in which the fitness of one is lowered by the presence of another Intraspecific competition is a particular form of competition in which members of the same Species vie for the same resource in an Ecosystem Courtship is the traditional dating period before engagement and marriage In Evolutionary biology, an evolutionary arms race is an Evolutionary struggle between competing sets of co-evolving Genes that develop adaptations Erotic capital is power possessed by an Individual as a result of their Sexual attractiveness to others The Irish Elk or Giant Deer, Megaloceros giganteus was a species of Megaloceros and one of the largest Deer that ever lived Koinophilia is a term used in Biology, meaning that when sexual creatures seek a mate they prefer that mate not to have any unusual peculiar or deviant features In the Evolutionary biology of Sexual reproduction, the operational sex ratio (OSR is the ratio of sexually competing male to females that are ready to mate Phylogenetic comparative methods (PCMs use information on the evolutionary relationships of organisms (phylogenetic trees to compare species (Harvey and Pagel 1991. Sex allocation is the allocation of resources to male versus female reproduction in sexual species (Charnov 1982 Sex ratio is the Ratio of Males to Females in a Population. The primary sex ratio is the ratio at the time of conception secondary sex ratio is NOTICE TO WOULD-BE-ROMEOS*************** Sexual conflict occurs when the two Sexes have conflicting optimal fitness strategies concerning Reproduction, leading to Evolutionary arms race A sexual field is an arena of social life whereby individuals compete for sexual status Sperm competition is " competition between Sperm of two or more Males for the Fertilization of an Ovum " (Parker 1970 (1871) The Descent of Man and Selection in Relation to Sex Murray, London
2. ^ Eberhard, WG. The Descent of Man and Selection in Relation to Sex is a book on Evolutionary theory by English naturalist Charles Darwin, first Sexual selection by cryptic female choice. Princeton, Princeton University Press. 1996.
3. ^ Maynard Smith, J (1982) Evolution and the Theory of Games. Maynard Smith redirects here -- for other uses see Maynard Smith (disambiguation Professor John Maynard Smith, F Evolution and the Theory of Games is a 1982 Book by the British evolutionary biologist John Maynard Smith on Evolutionary Cambridge University Press, pp. 131-137. ISBN 0-521-28884-3
4. ^ Ronald Fisher in a letter to Charles Galton Darwin, 22 November 1932, cited in Fisher, R. Sir Ronald Aylmer Fisher, FRS ( 17 February 1890 – 29 July 1962) was an English Statistician, Evolutionary Sir Charles Galton Darwin, KBE, MC, FRS (18 December 1887&ndash31 December 1962 was an English Physicist A. , Bennett, J. H. 1999. The genetical theory of natural selection: A complete variorum edition, Oxford University Press, Oxford, p. 308
5. ^ Lande, R. (1981) Models of speciation by sexual selection on polygenic traits. PNAS 78:3721-3725.
6. ^ Locke Rowe et Göran Arnvist "sexual conflict", 2005, Princeton Univ Press
7. ^ Thierry Lodé "La guerre des sexes chez les animaux " Eds Odile Jacob, Paris, 2006 ISBN 2-7381-1901-8
8. ^ PLoS ONE: Sexual Selection and the Evolution of Brain Size in Primates
9. ^ Dawkins, Richard [1978] (2006). Born in 1956 Thierry Lodé is a French biologist professor teaching Evolutionary ecology in the CNRS Units ETHOS (Ethology Evolution Ecology of Rennes1, France Clinton Richard Dawkins, FRS, FRSL (born 26 March 1941 is a British ethologist, evolutionary biologist, and Popular science The Selfish Gene, 30th anniversary edition, p158 endnote.  ““It is not implausible that , with natural selection refining their diagnostic skills, females could glean all sorts of clues about a male’s health, and robustness of his ability to cope with stress, from the tone and bearing of his penis. ”” 
10. ^ Roughgarden, J. , Oisho, M. and Akçay, E. (2006). "Reproductive social behaviour: cooperative games to replace sexual selection". Science 311: 965-969.   news  abstract.
11. ^ Dall, S. R. X. ; McNamara, J. M. , Wedell, N. and Hosken, D. J. (2006). "Debating sexual selection and mating strategies". Science 312: 689–697. doi:10.1126/science.312.5774.689b. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document. PMID 16675684.  
12. ^ For example, see Ruth Hubbard, “Have Only Men Evolved?” in The Politics of Women’s Biology (New Brunswick: Rutgers University Press, 1990), pp. Ruth Hubbard PhD was a Professor of Biology at Harvard University. 87-106.

References

• Abraham, J. N. (1998) La Saboteuse: An Ecological Theory of Sexual Dimorphism in Animals. Acta Biotheoretica 46 23-35 [2]
• Abraham, J. N. (2005) Insect Choice and Floral Size Dimorphism: Sexual Selection or Natural Selection? J. Insect Behavior, 18 743-756 [3]
• Andersson, M (1994) Sexual selection Princeton University Press. ISBN 0-691-00057-3
• Cronin, Helena (1991). Dr Helena Cronin is a noted Darwinian Philosopher and Rationalist. The ant and the peacock: altruism and sexual selection from Darwin to today. Cambridge University Press.
• Darwin, C (1871) The Descent of Man and Selection in Relation to Sex
• Fisher, RA (1930) The Genetical Theory of Natural Selection, Oxford University Press, ISBN 0-19-850440-3, Chapter 6 [4]
• Lande, CF R (1981). Charles Robert Darwin (February 12 1809 &ndash April 19 1882 was an English naturalist, who realised and demonstrated that all Species of life The Descent of Man and Selection in Relation to Sex is a book on Evolutionary theory by English naturalist Charles Darwin, first Sir Ronald Aylmer Fisher, FRS ( 17 February 1890 – 29 July 1962) was an English Statistician, Evolutionary The Genetical Theory of Natural Selection is a book by RA Fisher. Models of speciation by sexual selection on polygenic traits. Proc. Nat. Acad. Sci. , USA, 78 3721-5 [5]
• Miller, GF (1998) How mate choice shaped human nature: A review of sexual selection and human evolution. In C. Crawford & D. Krebs (Eds. ), Handbook of evolutionary psychology: Ideas, issues, and applications. Lawrence Erlbaum, pp. 87-129. [6]
• Miller, GF (2000) The Mating Mind: How sexual choice shaped the evolution of human nature. London: Heinemann. ISBN 0-434-00741-2
• Thierry, Lodé (20006) La guerre des sexes chez les animaux, Eds Odile Jacob . ISBN 2-7381-1901-8
• G Arnqvist & L Rowe (2005) "Sexual conflict" Princeton University Press

Further reading

Judson, Olivia (2003) Dr. Tatiana's Sex Advice to All Creation: Definitive Guide to the Evolutionary Biology of Sex. ISBN: 978-0099283751

Jolly, Allison (2001) Lucy's Legacy - Sex and Intelligence in Human Evolution. ISBN: 978-0674005402

Diamond, Jared (1997) Why is Sex Fun? The Evolution of Human Sexuality. ISBN: 978-0465031269

External links

• Sexual Selection: Stanford University
• The Great Debate: Sexual Selection
• An Introduction to Sexual Selection: University of Siegen
• Intralocus Sexual Conflict Diminishes the Benefits of Sexual Selection
• Review of GF Miller's The Mating Mind