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Topic: Evolution of sex

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	Evolution of sex - Wikipedia, the free encyclopedia
		The evolution of sex is a major puzzle in modern evolutionary biology.
		Evidence for this explanation for the evolution of sex is provided by comparison of the rate of molecular evolution of genes for kinases and immunoglobulins in the immune system with genes coding other proteins.
		Sex will act to recombine these genotypes, creating individuals with fewer and more deleterious mutations, and since there is a major selective disadvantage to individuals with more mutations, these individuals die out.
	en.wikipedia.org /wiki/Evolution_of_sex (2566 words)

	Whitehead Institute - Evolution of Sex Chromosomes
		Millions of years ago sex was probably determined not by sex chromosomes, but by some environmental factor, like the temperature of the water at which the egg incubated.
		(Sex determination still occurs this way in some animals like crocodiles and sea turtles.) Over the years, a pair of autosomes differentiated into two distinct chromosomes, the X and the Y. Today the X is still home to thousands of genes, but the Y has only a measly few dozen.
		During evolution, X-Y differentiation was probably initiated one stratum at a time, with stratum 1 having been the first to embark on the differentiation pathway and stratum 4 having been the most recent, says Dr. Lahn, who is now on the faculty at the University of Chicago.
	www.wi.mit.edu /news/archives/1999/dp_1029.html (976 words)

	The Evolution of Sex
		The cost of sex is shown to depend on the mating system, specifically on the fraction of monogamous matings, and may be much less than most estimates discussed previously in the literature.
		In this quotation, Maynard Smith is discussing models that synonymize the evolution of sex with the evolution of an increase in the recombination rate between two loci.
		Hence, the evolution of linkage relationships among loci may not be relevant to the evolution of sex.
	joandistrict6.com /sexevo.html (5776 words)

	Feminism, Male Sex, Evolution and Jail
		And further, in that evolution of 'pecking-order and survival-of-the-fittest', there is statistical realization of each, the muscular bravado of men and the 'Astarte being' of women, in the other sex.
		Thruout our evolution then, and in particular with respect to woman's life-style-and-quality compromised by 'men-and-their-sex', the general situation is that both men and women have always operated precisely (more or less) as they have evolved to operate, precisely (more or less) as they operated at their origins in coalescing deliberation.
		The civil, academic, business-world and all general disenfranchisements of women arose, essentially, only with women's evolutionally recent deliberation into the male 'provisional domain', and their sexual harass then, must be recognized only as 'continued male solicit/manipulation to procreate' as the evolved physiology of both would have them be(*3).
	condition.org /sexevolu.htm (1857 words)

	The Evolution of Sexual Reproduction
		The two-fold cost to sex refers to the fact that when sexual reproduction occurs, each reproducing individual passes on just one of the two alleles it has for each trait, but when asexual reproduction occurs, each reproducing individual passes on both alleles it has for each trait.
		Sex may by risky -- while mating one may be vulnerable to predation, and exposed to sexually transmitted diseases.
		Offspring are likely to be in an environment with parasites that have adapted to be able to attack their parents, so producing offspring that are genetically variable and not identical to either parent may result in offspring having higher resistance to parasites, and therefore better survival.
	www.utm.edu /departments/cens/biology/rirwin/391/391SexEvol.htm (1201 words)

	Zoology 500 D
		Sex allows advantageous alleles in different individuals to be combined together into the same individual.
		The fate of a beneficial mutation with sex and recombination depends less on the genetic background on which it arises (less interference among loci).
		Sex and recombination can regenerate the extreme genotypes that are underrepresented and increase the amount of genetic variance.
	www.zoology.ubc.ca /~otto/PopGen500/Discussion2/Overheads.html (832 words)

	Argument: Evolution of sex (Site not responding. Last check: 2007-11-07)
		Sex is said to be more important than life itself, since it enables genes to be passed on to succeeding generations.
		It is also biologically costly to maintain the sex organs, and to maintain mechanisms to stop the male’s immune system destroying his own (genetically different) sperm, and stop the female’s immune system destroying incoming sperm or the offspring she carries (in viviparous organisms).
		Evolution is supposed to be a race, and the asexual minnows produced clones, then stopped evolving, so are easy targets.
	www.answersingenesis.org /home/area/re2/chapter11.asp (2914 words)

	Sex — Evolution’s Janitor
		In mammals, sex is usually preceded by intricate mating behaviors.
		The researchers say that in the water flea, sex appears to have enabled the separation of beneficial and deleterious versions of genes, so natural selection could act more efficiently in favoring the good and weeding out the bad.
		The present report supports the notion that it is sex - or the genetic recombination that is a component of sexual reproduction - which is the purifying force that helps get rid of genetic mishaps that harm the overall evolutionary health of a population.
	www.scienceagogo.com /news/20060117001505data_trunc_sys.shtml (1095 words)

	Evolution - Sex Ratios
		The queen is equally related to her sons and daughters, and hence should favor a 1:1 sex ratio.
		Seychelles warblers adjust the primary sex ratio facultatively in response to the quality of the territory they inhabit and to the number of helpers present on the breeding territories.
		Cytoplasmically inherited factors that skew sex allocation towards females are known from a variety of plants and animals.
	core.ecu.edu /biol/summersk/summerwebpage/biol3520/EVOLsexratios.htm (893 words)

	Zoology 304, Evolution
		The acceleration of evolution should be favored by group (i.e., species) selection, based on both a higher rate of speciation and lower rate of extinction.
		But sex has become is so enmeshed in other features of genetic architecture that asexual the variants arise too infrequently for asexual reproduction to prevail.
		A lower proportion of either sex will make that sex disproportionately responsible for the next generation, so selection should favor greater production of that sex, as long as competition for mates is distributed among a large population.
	www.science.siu.edu /zoology/King/304/sex.htm (2074 words)

	Philipp's Homepage: Evolution of sex
		To find the reason for sex, we must investigate the effects of meiosis and syngamy, which are its defining characteristics, but absent from parthenogenesis.
		Firstly, sex is common in both animals and plants, whereas most taxa that reproduce parthenogenetically are of recent evolutionary origin, and polyphyletically distributed through animal and plant kingdoms, suggesting they are successful in the short term but tend to become extinct rather sooner.
		Furthermore, whilst the origin, and cause of evolution, of sex are not known, the sister phenomenon to natural selection, genetic drift, is acknowledged with a possible role in this causation.
	www.philippwesche.org /old1/es.html (2776 words)

	Newton's Binomium: Why do fish need bicycles?
		The evolution of sexual reproduction is one of the great mysteries of evolutionary biology.
		This is that the benefits of sex are not direct (in the sense that the offspring of sexually reproducing individuals have a higher mean fitness than those of asexually reproducing ones) but indirect such that the offspring of sexually reproducing individuals have a higher variance in fitness than that of asexually reproducing ones.
		The MDH is very attractive because, in order for sexual populations to overcome the two-fold cost of sex, only two things must be true, and these can, in principle, be tested using data from real organisms.
	newtonsbinomium.blogspot.com /2006/02/why-do-fish-need-bicycles.html (700 words)

	Evolution of Sex (Site not responding. Last check: 2007-11-07)
		According to evolutionary psychology many of the traditional and universal qualities which we find sexually appealing are grounded not merely in assimilated social cultural traditions as we have been told, but are deeply rooted in our basic physiological make-up: our unconscious innate drives to do our fair share for survival of the species.
		Sagan and Druyan (1992) points out that although most cultures have strict social or legal prohibitions against incestuous sexual liaisons, the avoidance of sex with blood relatives appears to a significant degree, to be an inborn taboo.
		As David Meyers (1995) states, sex differences and mate selection behaviors which may have once been helpful in ensuring the survival of our primitive ancestors and their young may no longer be adaptive and useful in today’s world.
	home.everestkc.net /pascal/evolsex.htm (3032 words)

	Evolution of Sex
		Subsequent evolution and maintenance of sex and recombination.
		The central problems with sex: 1) sex and recombination mix up any "coadaptation" that a genotype might have to a particular environment; why disturb this if its is adaptive; 2) there is a cost of meiosis associated with putting genes into males that cannot produce eggs.
		These two observations suggest that sex might evolve by group selection: we have 1) genetically isolated "groups" (sexual and parthenogenetic strains), 2) disadvantage to the individual and 3) advantageous to the long-term survival of the group.
	biomed.brown.edu /Courses/BIO48/19.Evol.of.Sex.HTML (1071 words)

	The Evolution of Sex -- Hines and Culotta 281 (5385): 1979 -- Science
		Ryan's article explores the evolution of mating preferences and discusses the effects of receiver bias--or, how beauty is in the eye of the beholder.
		Partridge and Hurst's article provides an overview of the often opposing forces driving the evolution of female and male and the molecular expressions of the war between the sexes.
		And Pennisi reports on one genetic weapon wielded in the battle of the sexes: genomic imprinting, in which genes from one parent are marked for later silencing or disposal.
	www.sciencemag.org /cgi/content/summary/281/5385/1979 (798 words)

	ScienceDaily: Evolution Of Sex Chromosomes: The Case Of The White Campion
		Similarities in sex chromosome evolution have been reported between birds and mammals (although in birds, females are the heterozygous sex).
		The theory of sex chromosome evolution holds that sex chromosomes were once homologs (a pair of equivalent autosomesthe non-sex chromosomes) that evolved different morphology and gene content because they lost their ability to recombine.
		Sex -- Sex refers to the male and female duality of biology and reproduction.
	www.sciencedaily.com /releases/2005/02/050201112231.htm (1975 words)

	[No title]
		Yet mammals have an XY system of sex determination, birds use ZW, while turtles and alligators determine sex by the temperature of the embryo during a specific point in development.
		Sex determination often comes down to the activity of a single gene, and whatever chromosome carries that gene winds up as the sex chromosome.
		At that point, the species is in danger of losing its entire sex determination mechanism, and the selective pressure shifts: the remainder of the sex chromosome comes under pressure to find a new home elsewhere in the genome.
	arstechnica.com /journals/science.ars/2006/2/19/2916 (2309 words)

	Evolution - A-Z - Sex: faster evolution
		The higher the rate at which favorable mutations are arising, the greater the evolutionary rate of a sexual relative to an asexual population.
		This is a case of group selection because it claims that the cost of sex is more than made up for by the faster evolution of the sexual population, or group.
		Figure: evolution in (a) asexual and (b) sexual populations.
	www.blackwellpublishing.com /ridley/a-z/Sex__faster_evolution.asp (338 words)

	Evolution and Sex
		Yet sex remains a mystery to researchers, to say nothing of the rest of the population.
		It suggests that sex would be favored by a variable environment, yet a close inspection of the global distribution of sex reveals that where environments are stable (such as in the tropics), sexual reproduction is most common.
		Evolution is dependent on change (the English word “evolution” derives from the Latin evolvere, meaning “to unroll, to change”).
	www.trueorigin.org /sex01.asp (5451 words)

	Evolution - Home
		Readable and stimulating, yet well balanced and in-depth, this text tells the story of evolution, from the history of the study to the most recent developments in evolutionary theory.
		The sections on adaptation and diversity have been reorganized for improved clarity and flow, and a completely updated section on the evolution of sex and the inclusion of more plant examples have all helped to shape this new edition.
		Evolution also features strong, balanced coverage of population genetics, and scores of new applied plant and animal examples make this edition even more accessible and engaging.
	www.blackwellpublishing.com /ridley (257 words)

	Evolution of Sexual Reproduction [M.Tevfik Dorak]
		This is currently the most widely favored theory on the evolution of sex.
		When, however, the cost of sex (this is the cost of males, mating and recombination) outweighs the benefits of sex, a species may switch back to asexual reproduction.
		One consequence of sexual reproduction is anisogamy (the existence of two kinds of gamete, eggs and sperm) which is the basis of morphological and behavioral differences between the sexes (see sexual selection).
	www.dorak.info /evolution/sreprod.html (1524 words)

	Evolution of sex: theory
		Thus, happily, parasites are not required to maintain sex in parasites, thereby avoiding an infinite regress.
		Parasitism, mutation accumulation and the maintenance of sex.
		The maintenance of sex by parasitism and mutation accumulation under epistatic fitness functions.
	www.indiana.edu /~curtweb/Research/sex&recomb.theory.html (549 words)

	Cornell News: sex pheromone evolution link
		In addition to explaining how pheromone evolution might have occurred in the past, the paper also demonstrates that the conditions required for dramatic shifts in pheromone blends could well be present today and in the future.
		Insect populations could be capable of shifting away from a pheromone blend being used for their control in the field, making such control ineffective.
		His research team will be working on the genomes of fruit flies, mosquitoes, crickets and silkworms to detect if these kinds of genes are present.
	www.news.cornell.edu /releases/Sept02/SexPheromoneRoelofs.html (669 words)

	Sex Speeds Up Evolution, Study Finds (Site not responding. Last check: 2007-11-07)
		To demonstrate this, a team of scientists created a mutant strain of yeast that, unlike normal yeast, was unable to divide into the sexual spores that allow yeast to engage in sexual reproduction.
		This shows "unequivocally that sex allows for more rapid evolution," said Matthew Goddard of the School of Biological Sciences at the University of Auckland in New Zealand.
		However, since then, evolutionary biologists have struggled to find a simple and general explanation for why sex comes in handy when it comes to the survival of the fittest.
	news.nationalgeographic.com /news/2005/03/0330_050330_sexevolution.html (441 words)

	Focus on Evolution of Sex
		The April issue of Nature Reviews Genetics is dedicated to these and related questions, with an emphasis on empirical studies that have become possible with the application of molecular genetic methods to evolutionary issues.
		The study of sex engages scientists from different areas of biology, who investigate how and why sex evolved in the first place, why it is maintained, and how the distinct morphology of the two sexes has developed and evolved in animals and plants.
		The problem of sex might be an old one, but the variety of issues it raises will continue to provide challenges for years to come.
	www.nature.com /nrg/focus/evolsex/index_mf.html (265 words)

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