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Topic: Sexual selection

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In the News (Sat 20 Apr 19)

  Sexual Selection [M.Tevfik Dorak]
Thus, the MHC may be involved in sexual selection as the genetic origin of the 'good genes' affecting the development of secondary sexual characters and the quality of the immune response both in intra and intersexual competition.
The selection for sperm may start as early as in the vagina, may involve the process called sperm capacitation in the uterus and the long journey of the sperm along the reproductive tract.
Sexual selection and speciation: Sexual selection affects the process of mating and the slightest change to the process of mating, if it prevents interbreeding, means a new species exists (via reproductive isolation mechanisms).
dorakmt.tripod.com /evolution/sselect.html   (3476 words)

 Sexual Selection, Stasis, Run-away Selection, Dimorphism and HumanEvolution
Sexual specialization is one reason that there is a difference between the sexes: often one sex raises the young and takes on the task of bringing them to a point of being able to take care of themselves.
Run-away sexual selection usually involves a feature in one sex that is not expressed in the other (or that is incompletely expressed), with the result being a marked sexual dimorphism, but this does not mean that all sexual dimorphism is due to run-away sexual selection.
What the sexual dimorphism demonstrates when it is involved with a run-away sexual selection feature, is which sex is being selected for the feature: the peacock sex with the big tail is the sex where the tail is being selected to be big.
mywebpage.netscape.com /RAZD8/sexual_selection.htm   (2528 words)

 Sexual Selection
In birds, the first form of sexual selection occurs when males compete for territories, as is obvious when those territories are on leks (traditional mating grounds).
That second type of sexual selection, in which one sex chooses among potential mates, appears to be the most common type among birds.
As evidence that such selection is widespread, consider the reversal of normal sexual differences in the ornamentation of some polyandrous birds.
www.stanford.edu /group/stanfordbirds/text/essays/Sexual_Selection.html   (1199 words)

 California Wild Summer 2005 - the Myth of Sexual Selection   (Site not responding. Last check: 2007-09-15)
Sexual selection theory also teaches that because eggs are larger and more expensive to produce, females must conserve this resource by playing hard to get.
To a naturalist, the failure of sexual- selection to describe and explain animal behavior is reason enough to reject it at this time.
To be clear, the scientific truth, or lack of it, of sexual selection is logically independent of its social implications.
www.calacademy.org /calwild/2005summer/stories/sexual.html   (2667 words)

 Sexual Selection   (Site not responding. Last check: 2007-09-15)
Darwin (1871) developed the notion of sexual selection because he realized that not all of the differences between males and females were due to their specialized roles in sexual reproduction.
Sexual Selection is also noteworthy because it has the potential to become a "runaway" process in which there is no obvious optimum set of characters.
Sexual selection may also play a role in the process of speciation because mate preferences are obvious foundations for premating reproductive isolating mechanisms.
www.towson.edu /~scully/sexual_selection.html   (1581 words)

 Sexual selection - Wikipedia, the free encyclopedia
Sexual selection is a theory proposed by Charles Darwin that states that the frequency of traits can increase or decrease depending on the attractiveness or fertility of the bearer.
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.
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.
en.wikipedia.org /wiki/Sexual_selection   (3573 words)

 A Review of Sexual Selection and Human Evolution:   (Site not responding. Last check: 2007-09-15)
Sexual selection's revival has been swift, dramatic, and unique:  Darwin's idea is, to my knowledge, the only major scientific theory ever to have been accepted after a century of condemnation.
Selection for direct provisioning must not be confused with the more common pattern of selection for good territories that happen to be defended by particular males.
Sexual selection through mate choice would be expected to operate in any sexually-reproducing lineage,  regardless of whether there were distinct sexes such as males and females.
www.unm.edu /~psych/faculty/mate_choice.htm   (7526 words)

 Female Sexual Selection
Sexual selection depends on the success of certain individuals over others of the same sex, in relation to the general conditions of life.
Moreover, the costs of sexual selection to the species as a whole may be minimal, and there may be substantial benefits in terms of population adaptability, speciation rates, evolutionary innovation, and even macroevolutionary success.
Whereas natural selection and male competition tend to produce convergent evolution onto rather mundane, pragmatic adaptations, sexual selection through female choice tends to produce divergent evolution that explores all the extreme corners of the vast space of beautiful morphologies and charming behaviors.
www.neoteny.org /a/sexualselection.html   (7215 words)

 Sexual selection
Sexual selection is clearly an instance of non-random mating.
In fact, sexual selection is equivalent to a type fertility selection, in terms of how genotype frequencies will change from one generation to the next.
Second, the evolution of a sexually selected trait involves two traits: the male characteristic that is being selected and a female preference for that trait.
darwin.eeb.uconn.edu /eeb348/lecture-notes/fertility/node3.html   (317 words)

 Introduction to Natural and Sexual Selection
Moreover, sexual selection can produce individuals with such elaborate ornaments that they must be either energetically costly to develop, costly to maintain, or even lead to a direct survival cost for the individual that bears the ornament.
Directional selection also has a unique effect on the population -- it leads to an evolutionary response to selection that changes the mean of the trait from one generation to the next if the trait has a heritable component.
Selection on maternal investment should have a genetic basis if the trait is to respond to natural selection and indeed egg size of the mother is positively correlated with egg size of daughter's.
bio.research.ucsc.edu /~barrylab/classes/animal_behavior/SELECT.HTM   (11775 words)

 Sexual Selection in Primates - Cambridge University Press   (Site not responding. Last check: 2007-09-15)
Sexual Selection in Primates is aimed at graduates and researchers in primatology, animal behaviour, evolutionary biology and comparative psychology.
Sexual selection and the careers of primate males: paternity concentration, dominance acquisition tactics and transfer decisions Maria A. van Noordwijk and Carel P. van Schaik; 13.
Sexual selection, measures of sexual selection and sexual dimorphism in primates J. Michael Plavcan; 14.
www.cambridge.org /uk/catalogue/catalogue.asp?isbn=052153738X   (432 words)

Finally, several bird-specific issues regarding sexual selection are discussed, including the evolution of sexual dimorphisms in monogamous species and the role of birdsong in female choice.
Møller (1994) defined sexual selection as occurring "as a result of a non-random association between a (secondary sexual) character and a component of mating success." This association will cause the character to be selected in a population, regardless of whether it is otherwise useful to an individual.
The second type of sexual selection is known as "mate choice." Under this model, a member of one sex, usually the female, selects a member of the other sex based on some character or behavior that makes him more appealing than other nearby males.
oak.cats.ohiou.edu /~jm703496/es-ssbrd.html   (4992 words)

 Sexual selection and the Male:Female Mortality Ratio by Daniel Kruger and Randolph Nesse
Sexual selection and the Male:Female Mortality Ratio by Daniel Kruger and Randolph Nesse
It illustrates how natural and sexual selection tend to maximize the survival of genes, sometimes at the expense of the survival of individuals.
The role of sexual selection is supported by the high correlation between excess male mortality and sexual size dimorphism across mammalian taxa, after controlling for the effects of phylogeny (Promislow, 1992).
human-nature.com /ep/articles/ep026685.html   (4548 words)

 Zoology 500 D
Sexual selection depends on the success of certain individuals over others of the same sex, in relation to the propagation of the species; while natural selection depends on the success of both sexes, at all ages, in relation to the general conditions of life.
The belief in the power of sexual selection rests chiefly on the following considerations: Certain characters are confined to one sex; and this alone renders it probable that in most cases they are connected with the act of reproduction.
Among the explanations for sexually dimorphic horns, antlers, tusks, and spurs, the empirical support is strongest for the idea that they have evolved and are favored in males as weapons in contests over females.
www.zoology.ubc.ca /~otto/PopGen500/Discussion3/Overheads.html   (1023 words)

 Modern History Sourcebook: Charles Darwin: The Descent of Man, 1871, excerpts
Sexual Selection depends on the success of certain individuals over others of the same sex, in relation to the propagation of the species; whilst Natural Selection depends on the success of both sexes, at all ages, in relation to the general conditions of life.
The sexual struggle is of two kinds; in the one it is between the individuals of the same sex, generally the males.
He who admits the principle of Sexual Selection will be led to the remarkable conclusion that the nervous system not only regulates most of the existing functions of the body, but has indirectly influenced the progressive development of various bodily structures and of certain mental qualities.
www.fordham.edu /halsall/mod/1871darwin-desc3.html   (2164 words)

 Sexual Selection
So far all of our discussions of selection have been without much regard for the sex of the individual under selection (evolution of the sex ratio to 1:1 can occur through selection for alleles in either males or females that favor the production of the rare sex).
But just as with natural selection individuals may differ in their ability to reproduce, in sexual selection there can be differential reproductive success among individuals of the same sex (and species).
Sexual selection occurs because there is a correlation between the gender of an individual and its parental investment in each offspring.
biomed.brown.edu /Courses/BIO48/18.Sexual.Selection.HTML   (1102 words)

 The Scientist : Sexual selection alternative slammed   (Site not responding. Last check: 2007-09-15)
In the review, Joan Roughgarden of Stanford University in California and two co-authors claim that sexual selection theory, which emphasizes the often-different interests of males and females, is fatally flawed.
Many critics argue that Roughgarden and her colleagues' theory is not exactly new -- and is, in fact, sexual selection in disguise.
"Sexual selection theory is not deeply flawed, and happily includes all of the points Roughgarden et al try and make," letter-writer David Shuker, at the University of Edinburgh, UK, told The Scientist.
www.the-scientist.com /news/display/23358   (591 words)

 NOVA Online | Flying Casanovas | Creature Courtship
Simply put, sexual selection is the evolutionary process that favors adaptations that increase an animal's chances of mating.
This kind favors the evolution of secondary sexual characters, such as large size and armaments like horns, that enhance a male's ability to fight.
The reason can be summed up in the phrase "sperm is cheap." Since males bear an inexhaustible supply of sperm, it's in their interest to copulate with as many females as possible, thereby engendering the most offspring.
www.pbs.org /wgbh/nova/bowerbirds/courtship.html   (776 words)

 Sexual Selection: Monkeys, Apes and Humans-Anth 1500   (Site not responding. Last check: 2007-09-15)
He viewed antlers and horns, for example, as having evolved in response to selection for fighting abilities among males; the most successful fighters gained access to females, and therefore passed on the characteristics that led to success in fighting to the next generation.
The critical observation linking sexual selection to mating systems was made by Huxley (1938), who noted that among polygynous species, the variance in male reproductive success is likely to be greater than the variance in female reproductive success.
There is much stronger selection on males to maximize matings, generating a difference in selective pressures on the sexes, and consequently sexual dimorphisms.
www.missouri.edu /~anthmark/courses/mah/lectures/sexualselection.htm   (1247 words)

 Evidence for Evolution: An Eclectic Survey
His theory of sexual selection was later expanded upon by Williams and Trivers.
If a sexual population has several different mutations in various genes in it's gene pool; it is possible through recombination to reconstruct an unmutated progeny.
Natural selection also changes allele frequencies.] The greater the bottleneck, the more severe the sampling error, or genetic drift, is. [Drift occurs to some degree in all population whether they are bottlenecked or not.
www.talkorigins.org /faqs/evolution-research.html   (14683 words)

 Sexual selection
sexually dimorphic traits like the peacock’s tail evolved through one mechanism of sexual selection known as
Human males are able to contribute substantial parental care, either directly or by provisioning the mother and her offspring, which can free women from work that conflicts with childcare.
  This fact sets up a kind of two-way street for human sexual selection: (1) Women should be choosy not only about the quality of her mate’s genes, but also about his willingness and ability to provide resources for childrearing.
www.wsu.edu /~rquinlan/Sexual_selection.htm   (2808 words)

 Runaway ornament diversity caused by Fisherian sexual selection -- Pomiankowski and Iwasa 95 (9): 5106 -- Proceedings ...
Selection on female preference is set to be 20% weaker in population 2, both for the individual cost of choice and epistasis in the joint cost of choice (population 1 b = 1.0,
Otherwise selection in the two populations is identical.
Sexual traits used in courtship appear to be exceedingly diverse across species (1, 2).
www.pnas.org /cgi/content/full/95/9/5106   (3913 words)

 Intensity of sexual selection along the anisogamy-isogamy continuum : Nature   (Site not responding. Last check: 2007-09-15)
Postcopulatory sexual selection on males (that is, sperm competition and cryptic female choice) can lead to decreased sperm numbers by favouring the production of larger sperm
As isogamy is approached (that is, as investment per gamete by males approaches that by females), sperm become less abundant, ova become relatively less rare, and competition between males for fertilization success is predicted to weaken.
Sexual selection for longer sperm, therefore, is expected to be self limiting.
www.nature.com /nature/journal/v441/n7094/abs/nature04683.html   (285 words)

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