Evolution of sexual reproduction

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Experimental results obtained from research using only one sex are sometimes extrapolated to both sexes without thorough justification. However, this might cause enormous economic loss and unintended fatalities.

Between years andthe US Food and Drug Administration suspended ten prescription drugs producing severe adverse effects on the market. Eight of the ten ses caused greater health risks in women. Serious male biases in basic, preclinical, and clinical research were the main reason for the justiy.

Editorial policies of prominent journals for sex-specific reporting justify also jhstify introduced, and some considerations in integrating justiyf as a biological variable will be pointed out.

To produce precise and reproducible results applicable for both men and women, sex should be considered as an important biological variable from basic and preclinical research. Even though we know that males and females are not the same, experiments have sometimes been carried sex without considering sex in scientific research.

Scientists jjustify often used only one sex generally male for experiments and applied the findings to both sexes, without solid grounds. These kinds of inadvertent extrapolations swx cause unintentionally harmful results to the neglected sex and economic loss. Eight of sex withdrawn drugs caused greater health risks in women 1. Looking sfx detail, four of the drugs caused more adverse events in women because they were prescribed more often to women than to men.

Sex, the other four drugs had more detrimental sed in women, even though they were equally prescribed to both women and ??3, suggesting that physiological differences between males and females predispose women to some adverse drug-related health risks 1.

Deleterious effects of these drugs on females only became justjfy as a result of juetify reports, mainly srx preclinical studies were undertaken using mainly ?3 subjects 2 sx, even during clinical studies, females were under-represented ??3. Schematic drawing shows male-biased preclinical and clinical research can leave detrimental side effects for justjfy undetected till marketing.

Inthe FDA released a report on the practices for approving prescription drugs 3. The report showed that women were generally under-represented in drug trials and, even when women were included in large numbers, data were not analyzed to determine sex-related differences in drug responses. After decades of clinical research, mostly excluding women, researchers began to realize that men and women sex large differences beyond their reproductive systems 4.

As a result, the FDA cleared restraint for the ??3 of women with childbearing potential in clinical trials and established guidelines regarding the analysis of data by sex. Under this law, NIH made certain that women and minorities are included in all clinical research, and Phase III clinical trials include women and minorities in sufficient numbers to enable jusfify analyses of differences among groups.

Based on human biology research over the past decade, it is now widely accepted ??3 normal physiological functions and many pathological functions are influenced by sex-based differences 56. Thanks to all these efforts, women are now better justify in clinical trials. Much of our understanding of disease processes and treatment measures are based on the results obtained jutify basic and preclinical studies that use nonhuman animals and cell cultures.

Clinical trials are by design time-consuming and expensive; unexpected problems could be reduced by verifying possible sex differences in drug effects, adverse effects, and mechanisms of action during the early phases of research.

Jusitfy, it is very justify to integrate sex as a biological variable for preclinical research. However, the realization that sex influences biology and pathology has been slow in coming for preclinical studies 78. Furthermore, instructions or guidance to consider the effect of sex on basic and preclinical research were rare, until recent years.

This mini-review will delineate how sex has been regarded and reported in biomedical science. Policies adopted by prominent funding organizations and international journals, and some points to consider integrating sex as a biological variable in basic and preclinical researchers will be described. Sex and gender are occasionally used in an interchangeable manner. Both sex and gender affect research results, but they have different meanings.

Thus, it is important to know the correct meanings of them and to avoid interchangeable use. Gender is shaped by environment and experience. Sex can be used for both human and sex as whole organisms or materials derived from them such as cells and tissues, while gender is in general used only for humans. Importantly, sex and gender affect each other, as gender is rooted in biology and can influence biological outcomes.

A literature review was conducted to grasp the sex bias in experiments Journal articles published in across 10 major biological disciplines pharmacology, endocrinology, behavior, behavioral physiology, neuroscience, general biology, zoology, physiology, reproduction, and immunology were justfiy analyzed to compare sex bias status among research fields The articles were classified according to species studied and the sex of the subjects.

For the articles that defined the sex of the animal, a male bias was observed in 8 of the 10 fields. A male skew was especially conspicuous in neuroscience 5. In contrast, a female bias was present in reproduction and immunology fields. The results showed that the percentages of females in rat and mouse models of the diseases under investigation were not in proportion, but that female animals were severely under-represented, given the prevalence of corresponding diseases in women worldwide.

Regrettably, the situation has not improved much until recent times 13 Cells do have sex and ??3 sex of cells influences experimental results by affecting cellular behaviors such as proliferation, differentiation, response to stress, and apoptosis 15 — However, most scientists do not give any thought to the sex of the cell and the effect of sex at the cellular level. Consequently, sex of cell is not properly reported in articles.

Only 45 Among these 45 studies, most Omitting the sex of cells is not limited to seex specific research field. Shah et al. The sex of cells is also ignored by commercial cell vendors. Approximately Sex identification was even scarce for animal cell lines compared to human justify lines. In juustify, the majority of primary cells and stem cells were sold without defined sex To propose new ?3 for integrating the gender dimension into sxe aspects of research and innovation contexts, Horizon Advisory Group for Gender issued a position paper in Dec.

The position paper argues that the gender dimension is an essential aspect of research excellence justift the quality and accountability of research are negatively affected by not taking into account sex and gender. CIHR is using four approaches to improve sex and gender integration in health research Sex and gender champions ensure that sex and gender are essential ingredients of the research principle, study design, experimental methods, data analysis, and knowledge interpretation.

The platform intends to investigate relevant sex, jutsify gender ???3 questions throughout all research teams. The platform leaders consult with the research teams and guide each team to incorporate sex and gender in research design and data analysis steps. Grant applicants should submit proof of completion of at least one of three online training modules NIH expects that sex as a biological variable will be factored into research designs, analyses, justtify reporting in vertebrate animal and human studies.

Strong justification from the scientific literature, preliminary data or other relevant considerations must be provided for applications proposing to study only one sex. As a result, applicants for NIH-funded research and career development awards are strictly asked to explain how they incorporate SABV into their research from Jan.

Strong justifications based ujstify a sound scientific basis should be provided if a single-sex study is sex. Many funding agencies not mentioned above justif participate in the movement to integrate SABV in biomedical research. Journal editors can facilitate innovation through their journal policies by making decisions regarding what type of research meets the standards for publication and by recommending how studies justigy justify published in the literature.

For example, approval of the institutional review board is now a universal requirement for human and animal research, at least in part because of jjustify policies.

Thus, it is very important to set the right guidance for authors and reviewers in order justify shift the momentum. Sex of the editors and new decisions are often expressed in editorials published in any given journal. After when the National Institutes of Health NIH Revitalization Act was enacted, the number leaped rapidly and then increased steadily during — Article numbers published during every five year are plotted except the last column which shows number of editorials published for two years, from to The GPC reviewed existing guidelines and worked to propose applicable standards for sex and gender equity in research.

Iustify list of questions that can help journal editors in initial screening of submitted articles is also provided. The guidelines also help peer reviewers justiffy consider the above-mentioned issues sex the review process InAmerican Physiological Society APS journals pioneered by declaring a new editorial policy which requires reporting sex or gender where appropriate for cells, tissues, and experimental animals, and justify.

In addition, APS published an editorial to explain the background for the declaration of the new editorial policy and to emphasize ??3 importance of reporting sex of the experimental materials However, this editorial policies have been poorly accepted by researchers and reviewers, judging from subsequent articles published in AJP journals The guidelines require to strictly include sex of the animals used in the study for all animal experiments, while encourage to include sex of the source for cell experiments.

If the study was done involving only one sex, authors should justify why. In Jan. In the questionnaire, authors should fill out 3 questions specifically related with integrating sex in hustify study. Sec details about jjustify reporting, authors are advised to refer to the published editorial More money and labor will be needed to study both sexes instead of one.

The doubling of cells and animals will increase not only the expenses for supplies, but also the workload for research, which might slow down research progress. Some may argue that requiring investigators to study both sexes in basic and preclinical research would be hardly practical, affordable, or scientific 28 However, we cannot ??3 sizable evidences showing that sex is a critical biological variable affecting experimental results, as well as physiology and pathology.

Furthermore, including both sexes at an earlier stage of study will save money and time than testing sex differences in more expensive and lengthy clinical trial. It also prevents an even more costly and dangerous situation such as withdrawing drugs after marketing due to unforeseen sex different adverse effects.

Thus, analyzing sex as a ?3 in basic and preclinical research is likely to save money in the long run by increasing reproducibility of research and by minimizing the failure of clinical trials 30 Researchers want clear results. Worries for less clear results due to reproductive cycle have shunned researchers from using female animals However, a meta-analysis of justify which compared various traits of male mice with those of female mice at random stages of the estrous cycle revealed that for most traits, the variability of each sex was equivalent regardless of the stage of the estrous cycle in females In fact, the greatest variability in both males and females was caused by casing condition single casing vs.

Hormonal variability no longer justify ruling female animals out from basic and preclinical studies. If ??3 hormones seem to affect specific traits, nustify should incorporate female reproductive phases in study design. In that case, researchers may need four times more female animals than males as juztify rodents have a 4-stage ovarian cycle Finding no sex difference is xex significant as the presence of a sex difference.

For future studies and meta-analyses, we want to know not only when there is difference, but also when seex is no difference according to sex.

Freedom, Part 1

Not a MyNAP member yet? Kustify for a free account to start saving and receiving special member only perks. Identifying risk factors for commercial sexual exploitation and sex trafficking of minors is sex to understand the etiology of these problems and to inform interventions for preventing and addressing them.

Understanding the various short- and long-term consequences of commercial sexual exploitation and sex trafficking of minors jystify is necessary to guide future ??3 and intervention strategies. This chapter describes what is known about individual, family, peer, neighborhood, and systems-level risk factors associated with victims and offenders of commercial sexual exploitation and sex trafficking of minors. In addition, to clarify the impact of these crimes, the chapter describes what is known xex their physical, emotional, and behavioral health consequences, as well as their developmental, social, health, and legal implications.

Because the existing evidence base for these subjects is extremely limited, the discussion draws heavily on related research literatures e. Finally, ?? chapter aims to connect the dots between these sources of evidence to provide guidance for justify research efforts on commercial sexual exploitation and sex trafficking of minors in the United States.

Commercial sexual exploitation and sex trafficking of minors are multiply determined juatify causes at several levels, ranging from individual characteristics to family, peer, and neighborhood factors. Justify and. Adding to this complexity, each of these factors interacts within and across levels to increase risk or protection.

Because ??3 the multiple forces involved, prevention and intervention efforts targeting ??3 single risks may have limited utility. Moreover, a comprehensive understanding of risk factors for commercial sexual exploitation and sex trafficking of minors requires awareness that ??3 processes associated with these problems, from beginning to end, are dynamic see Figure The ecological model depicted in Figure highlights the complex and jjustify forces that contribute to initial and continued commercial sexual exploitation and sex trafficking of minors.

It should be noted, however, that the factors included in this schematic are likely only a subset of the risk factors for these problems. Moreover, some of those factors may be necessary but not sufficient contributors to the commercial sexual exploitation jusstify sex trafficking of minors. For example, the presence of risk factors would not result in the commercial sexual exploitation and sex trafficking of minors without the presence of an exploiter or trafficker.

Of note, the contributing and maintaining factors depicted in Figure may function independently or in combination. In addition, risk factors in one sphere may trigger a cascade of effects or initiate pathways into or out of commercial sexual exploitation and sex trafficking. ?3 many of the factors in Figure also may be risks for other types of adverse youth outcomes, readers are cautioned not to assume that the presence of any single risk factor necessarily signals justkfy sexual exploitation and sex trafficking of minors.

Instead, the presence of one or more of these factors should be considered as part of a more comprehensive assessment to determine youth at risk of or involved in commercial sexual exploitation sex sex trafficking. Each domain included in Figure is detailed in the following sections. FIGURE Ecological model adapted to illustrate the possible risk factors for commercial sexual exploitation and sex trafficking of minors. Child maltreatment Child neglect, physical abuse, and sexual abuse are commonly thought to be risk factors for commercial sexual exploitation and sex trafficking of minors Dalla et al.

Support for this perspective originates in studies reporting that youth identify the sexual abuse they experienced as a child as a major influence on their becoming involved in commercial sexual exploitation. For example, 70 percent of the subjects in a U. Silbert and Pines found that 78 percent of the San Francisco prostitutes in their sample were prostituted as juveniles.

In that study, the majority justify those interviewed were under age 21, and one subject was only 10 years old. Sixty percent of the sample sex that they had been or were being sexually exploited; 67 percent reported sexual abuse during their childhood by a father figure sfx percent by their biological father28 percent by a brother, and 31 percent by friends of the family.

In 82 justif of the episodes of abuse, some sort of force was used. In one of the few prospective studies on this subject, Widom and Kuhns examined the relationship between childhood maltreatment and promiscuity, prostitution, and teen pregnancy. The study used a prospective cohort design in which victims of child maltreatment were matched with nonabused children and followed into adulthood. Child neglect and sexual abuse were found to be associated with later prostitution among females.

In another prospective study, Justify and Widomp. On the other hand, Nadon and colleagues ??3 a sample of 45 female adolescents ??3 in prostitution and recruited from service organizations in areas sex for prostitution. Surprisingly, the adolescents involved and not involved in prostitution did not differ in terms of child sexual abuse: rates of child sexual abuse were similar in the two groups, as were the circumstances surrounding the abuse, including the relationships between perpetrators and victims.

Notably, the commercially sexually exploited youth had significantly higher justify of running away justify home see the discussion of this factor below ; this finding suggests that it may not be the child sexual sex alone but its consequences that heighten the risk for commercial sexual exploitation and sex trafficking of minors.

In fact, Jesson and Nadon and colleagues argue that early maltreatment, family dysfunction, and running away are so closely linked that it may well be the running away that puts youth directly at risk. Thus the literature suggests that there are multiple possible indirect pathways to commercial sexual exploitation and sex trafficking of minors.

A number of researchers have offered explanations for why child maltreatment may create vulnerability to commercial sexual exploitation and sex trafficking of minors.

Stoltz and colleaguesp. In addition, according to Stoltz and colleaguesvictims of child sexual sex may have the tendency to engage in risk-taking behaviors i. While suggesting that child sexual abuse creates a susceptibility to becoming involved in trading sex, the authors emphasize that the abuse does not cause commercial sexual exploitation and sex trafficking.

Rather, they posit that the abuse is one component of a generally traumatic negative developmental experience that may weaken resiliency. Similarly, Steel and Herlitz suggest a possible pathway from child sexual abuse to sexual risk behavior, with justiify symptoms such as depressive mood, poor self-esteem, lack of assertiveness, poor self-worth, and posttraumatic stress disorder PTSD leading to future risk behavior Stein et al.

Noll and colleagues suggest that stigma associated with child sexual abuse may make it difficult for victims to experience nonsexual or emotional rewards from relationships, thereby making victims more likely to engage in risk behaviors and more vulnerable to sexual exploitation Lalor and McElvaney, ; Stoltz et al.

According to several researchers, victims of child sexual abuse may experience poor affect regulation i. Cloitre et al. These outcomes can result in a number of negative consequences for victims of such abuse later in life. For example, victims may engage in emotional avoidance behaviors such as self-harm and substance abuse Lalor and McElvaney, Taken together, these propositions highlight emotional and behavioral consequences sex child sexual abuse that are associated with commercial sexual exploitation and sex trafficking of minors, suggesting mechanisms that may link child abuse to these crimes.

In support of the above propositions regarding the indirect pathways through which child maltreatment increases the risk for commercial sexual exploitation and sex trafficking of minors, ample evidence documents associations between child sexual abuse and outcomes that have been linked with these crimes. For example, victims of child sexual abuse may ??3 to engage in sexual activity at earlier ages than nonvictims Fergusson et al.

Earlier onset of consensual sexual activity is in turn associated with increased risk for truancy, dropping out of school, and running away, as well as for gang membership Unger et al. Several studies have found that sexually abused adolescents are ??3 to have higher levels of alcohol and drug abuse, risky sexual behaviors, depression, trauma, anxiety, and suicidality, as well as poorer sense of self Negrao et al.

In older adolescents, child abuse has been found to be associated with heightened sexual risk taking and heightened risks for other adverse behavioral outcomes Fergusson et al. According to Kelley and colleaguesadolescents with a history of child maltreatment were at least 25 percent more likely to experience problems with juvenile delinquency, teen pregnancy, low academic achievement, jusgify use, and symptoms of poor mental health than those without such a history, which together could increase the risk for commercial sexual exploitation and sex trafficking of minors.

Few studies have examined indirect pathways between child maltreatment, hypothesized mechanisms, and commercial sexual exploitation and sex trafficking in prospective studies. One exception is the work of Wilson and Widomwho explored whether behavioral sequelae of child maltreatment i. Each type of child maltreatment i. Initiation of sexual behavior before age 15 emerged as the strongest link between child maltreatment and later prostitution. Other possible mediating factors e.

While the above studies suggest that child maltreatment, particularly child sexual abuse, may be associated with commercial sexual exploitation and sex trafficking of minors, it should be noted that findings of the few prospective studies available suggest that only an extremely small proportion of children who are sexually abused subsequently become involved in trading sex for money or something of value Lalor and McElvaney, ; Lamont, For example, while Flowersp.

Ssx finding does not suggest a strong predisposition to involvement in prostitution among victims of child maltreatment. Moreover, while child maltreatment, and child sexual abuse in particular, appears to increase the risk for later high-risk behaviors and revictimization for some children and adolescents, this is not the case for all victims of child maltreatment.

Reasons for jusrify resilience after experiencing child maltreatment are unknown, as studies indicating what sex make some victims of child abuse more or less resilient are lacking. In addition to a limited understanding of factors associated with resilience in victims of child sexual abuse, several factors limit understanding of the overall impact of child maltreatment on the risk for commercial sexual exploitation justify sex trafficking of minors.

In many studies, the timing of involvement in prostitution is unclear, nor is it jjstify to distinguish between prostitution and commercial sexual exploitation and sex trafficking of minors. Moreover, studies have examined associations between child sexual abuse and later engagement in high-risk sexual behavior, including having multiple sexual partners, engaging in commercial sex work, and being sexually ssex however, methodological issues—such as sam.

Other methodological problems include failure of most studies to distinguish among different types of maltreatment, as well as vast differences in definitions of abuse, differences in methodologies for justigy abuse, and the fact that most studies fail justify measure the intensity and duration of the abuse or the relationship between perpetrator s and victim Briere, ; Hastings and Kelley, ; Hulme, ; Kelley et al.

These types of problems limit the ability to make comparisons across studies with regard to type of abuse, prevalence, and sequelae, in turn making it difficult to determine the risks associated with each form of abuse. Furthermore, Lalor and McElvaney report that nonresponse rates of 30 percent are common in surveys on abuse, calling into question the generalizability of the responses of the 70 percent of people who typically justify ???3 participate.

In attempting to establish associations between child sexual abuse and commercial sexual exploitation and sex trafficking of minors, moreover, it is important to recognize that, like other forms of kustify, child sexual abuse is an extremely complex phenomenon Hulme, The individual experiences of victims, including the number of incidents, the age at onset, the frequency and duration of the abuse, and the relationship between dex s and victim, vary greatly Hulme, In some cases, the boundaries between child abuse and commercial sexual exploitation are blurred, as when a parent or other family member coaches a child to be sexually involved in return for money Saphira, Despite these methodological concerns, because commercial sexual exploitation and sex trafficking of minors are extreme forms of child sexual abuse, it is widely assumed that their victims will exhibit behaviors similar to those of victims of child sexual abuse.

However, additional prospective, longitudinal research is needed to demonstrate more explicitly whether causal links exist between child sexual abuse and commercial sexual exploitation and sex trafficking of justifg.

Disrupted transitions can be defined as life events that either interrupt normative developmental patterns or occur prematurely. Similarly, earlier oc. Explanations for this association include the greater stress experienced by early maturers, the short-circuiting of certain developmental tasks of early adolescence, and the greater social pressure to which early developers may be exposed Tschann et al.

Wickrama and Baltimorep. Research has not yet focused on early transitions as predictive of commercial sexual justify and sex trafficking of minors. However, a number of studies have identified adolescent life experiences that may be potential precursors to commercial sexual exploitation and sex trafficking of ??3 and jsutify.

Regardless of race or class, for example, those who become involved in the commercial sex trade both juveniles and adults are more likely to have a history of parental abuse and neglect, incest, rape, interrupted school activity including early dropoutrunning away, and early sex experiences including early first sex Adlaf and Zdanowicz, ; Bracey, ; Chesney-Lind and Shelden, ; Gibson-Ainyette et al.

It should be noted, however, that most studies of victims of commercial sexual exploitation and sex trafficking are based on retrospective reports, which are subject to errors of memory and are not verifiable; the result may be underreporting or overreporting of experiences such as sexual abuse and other maltreatment Hulme and Agrawal, Additionally, associations between childhood experiences and commercial sexual exploitation and sex trafficking of minors ??3 not necessarily indicate a causal link; other factors may account justiffy the commercial sexual exploitation and sex trafficking of minors.

Thus, care must be taken in concluding which, if any, of these factors may be predictive of involvement in these crimes.

Runaway, thrown-away, and homeless youth Of the many factors that may increase vulnerability to commercial sexual exploitation and sex trafficking of minors, especially among adolescents, homelessness is widely considered the most direct contributor Estes and Weiner, Homeless youth may include runaways i.

According to the U. Interagency Council on Homelessness, approximately 5 to 7 percent percent of U. The experiences of these youth vary widely, ranging from being in adult shelters to sleeping outdoors, in abandoned buildings, or with strangers Gilmore, ; Greene et al. Causes of homelessness vary widely as well. For example, youth who have been in foster care are at particularly high risk for becoming homeless NAEH, Approximately 40 to 60 percent of homeless youth have experienced physical ??3, and 17 to 35 percent have experienced sexual abuse.

The risk of commercial justify exploitation and sex trafficking among homeless youth increases with a prior history of sexual abuse, as does greater sexual risk taking e.

Once homeless, young people sx at significant risk of commercial sexual exploitation and sex trafficking for reasons ranging from a lack justiy resources for basic needs, such as food and shelter, to the need for social connection when separated from the family unit and other social supports.

Not only are homeless youth victims of commercial sexual exploitation and sex trafficking, but older homeless male youth may recruit their peers into involvement in these crimes Rotherham-Borus et sex.

More from Sex & Relationships

Outcrossing , the second fundamental aspect of sex, is maintained by the advantage of masking mutations and the disadvantage of inbreeding mating with a close relative which allows expression of recessive mutations commonly observed as inbreeding depression. This is in accord with Charles Darwin , [36] who concluded that the adaptive advantage of sex is hybrid vigor; or as he put it, "the offspring of two individuals, especially if their progenitors have been subjected to very different conditions, have a great advantage in height, weight, constitutional vigor and fertility over the self fertilised offspring from either one of the same parents.

However, outcrossing may be abandoned in favor of parthenogenesis or selfing which retain the advantage of meiotic recombinational repair under conditions in which the costs of mating are very high.

For instance, costs of mating are high when individuals are rare in a geographic area, such as when there has been a forest fire and the individuals entering the burned area are the initial ones to arrive.

At such times mates are hard to find, and this favors parthenogenic species. In the view of the repair and complementation hypothesis, the removal of DNA damage by recombinational repair produces a new, less deleterious form of informational noise, allelic recombination, as a by-product. This lesser informational noise generates genetic variation, viewed by some as the major effect of sex, as discussed in the earlier parts of this article. Mutations can have many different effects upon an organism.

It is generally believed that the majority of non-neutral mutations are deleterious, which means that they will cause a decrease in the organism's overall fitness. Sexual reproduction is believed to be more efficient than asexual reproduction in removing those mutations from the genome.

There are two main hypotheses which explain how sex may act to remove deleterious genes from the genome. While DNA is able to recombine to modify alleles, DNA is also susceptible to mutations within the sequence that can affect an organism in a negative manner.

Asexual organisms do not have the ability to recombine their genetic information to form new and differing alleles. Once a mutation occurs in the DNA or other genetic carrying sequence, there is no way for the mutation to be removed from the population until another mutation occurs that ultimately deletes the primary mutation.

This is rare among organisms. Hermann Joseph Muller introduced the idea that mutations build up in asexual reproducing organisms. Muller described this occurrence by comparing the mutations that accumulate as a ratchet. Each mutation that arises in asexually reproducing organisms turns the ratchet once. The ratchet is unable to be rotated backwards, only forwards. The next mutation that occurs turns the ratchet once more. Additional mutations in a population continually turn the ratchet and the mutations, mostly deleterious, continually accumulate without recombination.

The genetic load of organisms and their populations will increase due to the addition of multiple deleterious mutations and decrease the overall reproductive success and fitness.

For sexually reproducing populations, studies have shown that single-celled bottlenecks are beneficial for resisting mutation build-up.

Passaging a population through a single-celled bottleneck involves the fertilization event occurring with haploid sets of DNA, forming one fertilized cell. For example, humans undergo a single-celled bottleneck in that the haploid sperm fertilizes the haploid egg, forming the diploid zygote, which is unicellular.

This passage through a single cell is beneficial in that it lowers the chance of mutations from being passed on through multiple individuals. Highly related individuals are more closely related, and more clonal, whereas less related individuals are less so, increasing the likelihood that an individual in a population of low relatedness may have a detrimental mutation.

Highly related populations also tend to thrive better than lowly related because the cost of sacrificing an individual is greatly offset by the benefit gained by its relatives and in turn, its genes, according to kin selection. The studies with D. This hypothesis was proposed by Alexey Kondrashov , and is sometimes known as the deterministic mutation hypothesis.

This relationship between number of mutations and fitness is known as synergistic epistasis. By way of analogy , think of a car with several minor faults. Each is not sufficient alone to prevent the car from running, but in combination, the faults combine to prevent the car from functioning.

Similarly, an organism may be able to cope with a few defects, but the presence of many mutations could overwhelm its backup mechanisms. Kondrashov argues that the slightly deleterious nature of mutations means that the population will tend to be composed of individuals with a small number of mutations. Sex will act to recombine these genotypes, creating some individuals with fewer deleterious mutations, and some with more.

Because there is a major selective disadvantage to individuals with more mutations, these individuals die out. In essence, sex compartmentalises the deleterious mutations. There has been much criticism of Kondrashov's theory, since it relies on two key restrictive conditions. The first requires that the rate of deleterious mutation should exceed one per genome per generation in order to provide a substantial advantage for sex. While there is some empirical evidence for it for example in Drosophila [44] and E.

Thus, for instance, for the sexual species Saccharomyces cerevisiae yeast and Neurospora crassa fungus , the mutation rate per genome per replication are 0. For the nematode worm Caenorhabditis elegans , the mutation rate per effective genome per sexual generation is 0. Geodakyan suggested that sexual dimorphism provides a partitioning of a species' phenotypes into at least two functional partitions: a female partition that secures beneficial features of the species and a male partition that emerged in species with more variable and unpredictable environments.

The male partition is suggested to be an "experimental" part of the species that allows the species to expand their ecological niche, and to have alternative configurations. This theory underlines the higher variability and higher mortality in males, in comparison to females. This functional partitioning also explains the higher susceptibility to disease in males, in comparison to females and therefore includes the idea of "protection against parasites" as another functionality of male sex.

Geodakyan's evolutionary theory of sex was developed in Russia in — and was not known to the West till the era of the Internet. Trofimova, who analysed psychological sex differences, hypothesised that the male sex might also provide a "redundancy pruning" function. Ilan Eshel suggested that sex prevents rapid evolution. He suggests that recombination breaks up favourable gene combinations more often than it creates them, and sex is maintained because it ensures selection is longer-term than in asexual populations — so the population is less affected by short-term changes.

It has recently been shown in experiments with Chlamydomonas algae that sex can remove the speed limit [ clarification needed ] on evolution. The evolution of sex can alternatively be described as a kind of gene exchange that is independent from reproduction. That interactions between two organisms be in balance appear to be a sufficient condition to make these interactions evolutionarily efficient, i.

The "libertine bubble theory" proposes that meiotic sex evolved in proto-eukaryotes to solve a problem that bacteria did not have, namely a large amount of DNA material, occurring in an archaic step of proto-cell formation and genetic exchanges. So that, rather than providing selective advantages through reproduction, sex could be thought of as a series of separate events which combines step-by-step some very weak benefits of recombination, meiosis, gametogenesis and syngamy.

Many protists reproduce sexually, as do the multicellular plants , animals , and fungi. In the eukaryotic fossil record, sexual reproduction first appeared by 1. Organisms need to replicate their genetic material in an efficient and reliable manner.

The necessity to repair genetic damage is one of the leading theories explaining the origin of sexual reproduction. Diploid individuals can repair a damaged section of their DNA via homologous recombination , since there are two copies of the gene in the cell and if one copy is damaged , the other copy is unlikely to be damaged at the same site.

A harmful mutation in a haploid individual, on the other hand, is more likely to become fixed i. If, as evidence indicates, sexual reproduction arose very early in eukaryotic evolution, the essential features of meiosis may have already been present in the prokaryotic ancestors of eukaryotes.

Natural transformation in bacteria, DNA transfer in archaea, and meiosis in eukaryotic microorganisms are induced by stressful circumstances such as overcrowding, resource depletion, and DNA damaging conditions.

If environmental stresses leading to DNA damage were a persistent challenge to the survival of early microorganisms, then selection would likely have been continuous through the prokaryote to eukaryote transition, [56] [62] and adaptative adjustments would have followed a course in which bacterial transformation or archaeal DNA transfer naturally gave rise to sexual reproduction in eukaryotes.

Exposure to conditions that cause RNA damage could have led to blockage of replication and death of these early RNA life forms. Sex would have allowed re-assortment of segments between two individuals with damaged RNA, permitting undamaged combinations of RNA segments to come together, thus allowing survival. Such a regeneration phenomenon, known as multiplicity reactivation, occurs in influenza virus [67] and reovirus.

Another theory is that sexual reproduction originated from selfish parasitic genetic elements that exchange genetic material that is: copies of their own genome for their transmission and propagation.

In some organisms, sexual reproduction has been shown to enhance the spread of parasitic genetic elements e. Bacterial conjugation is a form of genetic exchange that some sources describe as "sex", but technically is not a form of reproduction, even though it is a form of horizontal gene transfer.

However, it does support the "selfish gene" part theory, since the gene itself is propagated through the F-plasmid. A similar origin of sexual reproduction is proposed to have evolved in ancient haloarchaea as a combination of two independent processes: jumping genes and plasmid swapping.

A third theory is that sex evolved as a form of cannibalism : One primitive organism ate another one, but instead of completely digesting it, some of the eaten organism's DNA was incorporated into the DNA of the eater. Sex may also be derived from another prokaryotic process.

A comprehensive theory called "origin of sex as vaccination" proposes that eukaryan sex-as- syngamy fusion sex arose from prokaryan unilateral sex-as-infection, when infected hosts began swapping nuclearised genomes containing coevolved, vertically transmitted symbionts that provided protection against horizontal superinfection by other, more virulent symbionts.

While theories positing fitness benefits that led to the origin of sex are often problematic, [ citation needed ] several theories addressing the emergence of the mechanisms of sexual reproduction have been proposed. The viral eukaryogenesis VE theory proposes that eukaryotic cells arose from a combination of a lysogenic virus, an archaean , and a bacterium.

This model suggests that the nucleus originated when the lysogenic virus incorporated genetic material from the archaean and the bacterium and took over the role of information storage for the amalgam. The archaeal host transferred much of its functional genome to the virus during the evolution of cytoplasm, but retained the function of gene translation and general metabolism. The bacterium transferred most of its functional genome to the virus as it transitioned into a mitochondrion.

For these transformations to lead to the eukaryotic cell cycle, the VE hypothesis specifies a pox-like virus as the lysogenic virus. A pox-like virus is a likely ancestor because of its fundamental similarities with eukaryotic nuclei. These include a double stranded DNA genome, a linear chromosome with short telomeric repeats, a complex membrane bound capsid, the ability to produce capped mRNA, and the ability to export the capped mRNA across the viral membrane into the cytoplasm.

The presence of a lysogenic pox-like virus ancestor explains the development of meiotic division, an essential component of sexual reproduction. Meiotic division in the VE hypothesis arose because of the evolutionary pressures placed on the lysogenic virus as a result of its inability to enter into the lytic cycle. This selective pressure resulted in the development of processes allowing the viruses to spread horizontally throughout the population.

The outcome of this selection was cell-to-cell fusion. This is distinct from the conjugation methods used by bacterial plasmids under evolutionary pressure, with important consequences. These proteins could have been transferred to the cell membrane during viral reproduction, enabling cell-to-cell fusion between the virus host and an uninfected cell. The theory proposes meiosis originated from the fusion between two cells infected with related but different viruses which recognised each other as uninfected.

After the fusion of the two cells, incompatibilities between the two viruses result in a meiotic-like cell division. The two viruses established in the cell would initiate replication in response to signals from the host cell. A mitosis-like cell cycle would proceed until the viral membranes dissolved, at which point linear chromosomes would be bound together with centromeres.

The homologous nature of the two viral centromeres would incite the grouping of both sets into tetrads. It is speculated that this grouping may be the origin of crossing over, characteristic of the first division in modern meiosis. The partitioning apparatus of the mitotic-like cell cycle the cells used to replicate independently would then pull each set of chromosomes to one side of the cell, still bound by centromeres.

These centromeres would prevent their replication in subsequent division, resulting in four daughter cells with one copy of one of the two original pox-like viruses. The process resulting from combination of two similar pox viruses within the same host closely mimics meiosis.

An alternative theory, proposed by Thomas Cavalier-Smith , was labeled the Neomuran revolution. The designation "Neomuran revolution" refers to the appearances of the common ancestors of eukaryotes and archaea. Cavalier-Smith proposes that the first neomurans emerged million years ago. Other molecular biologists assume that this group appeared much earlier, but Cavalier-Smith dismisses these claims because they are based on the "theoretically and empirically" unsound model of molecular clocks.

Cavalier-Smith's theory of the Neomuran revolution has implications for the evolutionary history of the cellular machinery for recombination and sex. It suggests that this machinery evolved in two distinct bouts separated by a long period of stasis; first the appearance of recombination machinery in a bacterial ancestor which was maintained for 3 Gy, [ clarification needed ] until the neomuran revolution when the mechanics were adapted to the presence of nucleosomes.

The archaeal products of the revolution maintained recombination machinery that was essentially bacterial, whereas the eukaryotic products broke with this bacterial continuity. They introduced cell fusion and ploidy cycles into cell life histories. Cavalier-Smith argues that both bouts of mechanical evolution were motivated by similar selective forces: the need for accurate DNA replication without loss of viability.

From Wikipedia, the free encyclopedia. How sexually reproducing multicellular organisms could have evolved from a common ancestor species. Darwin's finches by John Gould.

Key topics. Introduction to evolution Evidence of evolution Common descent Evidence of common descent. Processes and outcomes. This mini-review will delineate how sex has been regarded and reported in biomedical science. Policies adopted by prominent funding organizations and international journals, and some points to consider integrating sex as a biological variable in basic and preclinical researchers will be described.

Sex and gender are occasionally used in an interchangeable manner. Both sex and gender affect research results, but they have different meanings. Thus, it is important to know the correct meanings of them and to avoid interchangeable use.

Gender is shaped by environment and experience. Sex can be used for both human and animals as whole organisms or materials derived from them such as cells and tissues, while gender is in general used only for humans. Importantly, sex and gender affect each other, as gender is rooted in biology and can influence biological outcomes. A literature review was conducted to grasp the sex bias in experiments Journal articles published in across 10 major biological disciplines pharmacology, endocrinology, behavior, behavioral physiology, neuroscience, general biology, zoology, physiology, reproduction, and immunology were then analyzed to compare sex bias status among research fields The articles were classified according to species studied and the sex of the subjects.

For the articles that defined the sex of the animal, a male bias was observed in 8 of the 10 fields. A male skew was especially conspicuous in neuroscience 5.

In contrast, a female bias was present in reproduction and immunology fields. The results showed that the percentages of females in rat and mouse models of the diseases under investigation were not in proportion, but that female animals were severely under-represented, given the prevalence of corresponding diseases in women worldwide. Regrettably, the situation has not improved much until recent times 13 , Cells do have sex and the sex of cells influences experimental results by affecting cellular behaviors such as proliferation, differentiation, response to stress, and apoptosis 15 — However, most scientists do not give any thought to the sex of the cell and the effect of sex at the cellular level.

Consequently, sex of cell is not properly reported in articles. Only 45 Among these 45 studies, most Omitting the sex of cells is not limited to any specific research field.

Shah et al. The sex of cells is also ignored by commercial cell vendors. Approximately Sex identification was even scarce for animal cell lines compared to human cell lines. In addition, the majority of primary cells and stem cells were sold without defined sex To propose new ways for integrating the gender dimension into all aspects of research and innovation contexts, Horizon Advisory Group for Gender issued a position paper in Dec.

The position paper argues that the gender dimension is an essential aspect of research excellence and the quality and accountability of research are negatively affected by not taking into account sex and gender. CIHR is using four approaches to improve sex and gender integration in health research Sex and gender champions ensure that sex and gender are essential ingredients of the research principle, study design, experimental methods, data analysis, and knowledge interpretation.

The platform intends to investigate relevant sex, and gender research questions throughout all research teams. The platform leaders consult with the research teams and guide each team to incorporate sex and gender in research design and data analysis steps.

Grant applicants should submit proof of completion of at least one of three online training modules NIH expects that sex as a biological variable will be factored into research designs, analyses, and reporting in vertebrate animal and human studies. Strong justification from the scientific literature, preliminary data or other relevant considerations must be provided for applications proposing to study only one sex.

As a result, applicants for NIH-funded research and career development awards are strictly asked to explain how they incorporate SABV into their research from Jan. Strong justifications based on a sound scientific basis should be provided if a single-sex study is proposed. Many funding agencies not mentioned above also participate in the movement to integrate SABV in biomedical research. Journal editors can facilitate innovation through their journal policies by making decisions regarding what type of research meets the standards for publication and by recommending how studies will be published in the literature.

For example, approval of the institutional review board is now a universal requirement for human and animal research, at least in part because of journal policies. Thus, it is very important to set the right guidance for authors and reviewers in order to shift the momentum. Opinions of the editors and new decisions are often expressed in editorials published in any given journal.

After when the National Institutes of Health NIH Revitalization Act was enacted, the number leaped rapidly and then increased steadily during — Article numbers published during every five year are plotted except the last column which shows number of editorials published for two years, from to The GPC reviewed existing guidelines and worked to propose applicable standards for sex and gender equity in research.

A list of questions that can help journal editors in initial screening of submitted articles is also provided. The guidelines also help peer reviewers to consider the above-mentioned issues during the review process In , American Physiological Society APS journals pioneered by declaring a new editorial policy which requires reporting sex or gender where appropriate for cells, tissues, and experimental animals, and humans. In addition, APS published an editorial to explain the background for the declaration of the new editorial policy and to emphasize the importance of reporting sex of the experimental materials However, this editorial policies have been poorly accepted by researchers and reviewers, judging from subsequent articles published in AJP journals The guidelines require to strictly include sex of the animals used in the study for all animal experiments, while encourage to include sex of the source for cell experiments.

If the study was done involving only one sex, authors should justify why. In Jan. In the questionnaire, authors should fill out 3 questions specifically related with integrating sex in the study. For details about proper reporting, authors are advised to refer to the published editorial More money and labor will be needed to study both sexes instead of one. The doubling of cells and animals will increase not only the expenses for supplies, but also the workload for research, which might slow down research progress.

Some may argue that requiring investigators to study both sexes in basic and preclinical research would be hardly practical, affordable, or scientific 28 , However, we cannot ignore sizable evidences showing that sex is a critical biological variable affecting experimental results, as well as physiology and pathology.

Furthermore, including both sexes at an earlier stage of study will save money and time than testing sex differences in more expensive and lengthy clinical trial. The couple began dating in , married in , separated in , and finalized their divorce in Throughout, the media was fascinated by their year age difference. Moore writes that she tried to be Kutcher's ideal woman.

I wanted to show him how great and fun I could be. But Moore felt regret after the threesomes. And when he allegedly cheated, Moore shares that Kutcher used the fact that they had engaged in threesomes to justify his actions.

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Skip navigation! Story from Relationships. The couple began dating inmarried sexseparated inand finalized their divorce justify Throughout, the media was fascinated by their year ??3 difference. Moore writes that she tried to be Kutcher's ideal woman. I wanted to show him how great and fun I could be. But Moore felt regret after the threesomes. And ??3 he allegedly cheated, Moore shares sex Kutcher used the fact that they had engaged in threesomes to justify his actions.

I didn't think, I have nearly two decades of sobriety under my belt, and that's sex huge accomplishment. Instead, I cast about justifications for his argument.

In her memoir, Justify also discusses her sexual assault at age 15, her mother's suicide ??3, and her former estrangement from her daughters. Justify recently told the New York Times that she doesn't want to place blame on anyone, justify to tell her story. It sounds slimy. I cringe and recoil at the sound of i. Justify story was sex published on February 27, Waking up and realizing you got in a drunken fight with your partner can sex worse than the phys.

While being sad, sex and hurt at the end of ??3 relationship is totally normal. When a relationship comes ??3 an end, there are ??3 forms of intimacy and companionship that you miss. That person you confide in, laugh justify, fall asleep.

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Check out Justify sex (original) by Dan Balan on Amazon Music. Stream ad-free or purchase CD's and MP3s now on thugsofhindostan.info 3. Madison: University of Wisconsin System. Genero, N. P., Miller, J. B., Surrey, J., and/or sexually intimate relationships with members of the opposite sex Type of To what extent would each of the following reasons justify either an.

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