History of Sex: The Middle Ages (Documentary)
Thanks to thee unrealistic standards constantly portrayed in media , we've all built up this imaginary idea of what sex is supposed to be like. Some people expect a romantic night of candles and passion, while others think it will be the most pleasure they've ever felt in their whole life. But the truth is, everyone's experience is different. Sometimes it's smooth and romantic and lives up to your expectations, while other times, it's kind of terrible. But no matter how old you are or what the circumstances are, having sex for the first time can feel like a huge deal! So, to give you a better idea about what your first time may be like, we talked to 43 girls about the first time they had sex - how they knew they were ready, who they did it with, and how they felt afterward. I think I would have enjoyed it more if he had checked in with me to see if my needs were being met, which they weren't.
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 Kondrashovand is sometimes known as the deterministic mutation hypothesis.
This relationship between number of mutations and fitness is known as synergistic epistasis.
Beginning of sex
By way of analogythink 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  and E. Thus, for instance, for the sexual species Saccharomyces cerevisiae yeast and Neurospora crassa fungusthe mutation rate per genome per replication are 0.
For the nematode worm Caenorhabditis elegansthe 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 uheynounce.comedictable 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.
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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. Stephen Howard and Curtis Lively were the first to suggest that the combined effects of parasitism and mutation accumulation can lead to an increased advantage to sex under conditions not otherwise predicted Nature, Using computer simulations, they showed that when the two mechanisms act simultaneously the advantage to sex over asex is larger than for either factor operating alone.
Many protists reproduce sexually, as do the multicellular plantsanimalsand 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.
Evolution of sexual reproduction
Diploid individuals can repair a damaged section of their DNA via homologous recombinationsince there are two copies of the gene in the cell and if one copy is damage 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. In bacteria, these stresses induce an altered physiologic state, termed competence, that allows active take-up of DNA from a donor bacterium and the integration of this DNA into the recipient genome see Natural competence allowing recombinational repair of the recipients' damaged DNA.
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,   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  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 archaeanand 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-Smithwas 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.
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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.
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Key topics. Introduction to evolution Evidence of evolution Common descent Evidence of common descent.
Processes and outcomes. Natural history. History of evolutionary theory. Fields and applications. Applications of evolution Biosocial criminology Ecological genetics Evolutionary aesthetics Evolutionary anthropology Evolutionary computation Evolutionary ecology Evolutionary economics Evolutionary epistemology Evolutionary ethics Evolutionary game theory Evolutionary linguistics Evolutionary medicine Evolutionary neuroscience Evolutionary physiology Evolutionary psychology Experimental evolution Phylogenetics Paleontology Selective breeding Speciation experiments Sociobiology Systematics Universal Darwinism.
Social implications. Evolution as fact and theory Social effects Creation-evolution controversy Objections to evolution Level of support. See also: Hill-Robertson effect. Main article: Muller's ratchet. Life timeline. This box: view talk edit. Single-celled life. Multicellular life. Earliest water. Earliest life. Gorgeous teen babe has sex for the first time on camera 5 min Parabertasol - First time sex for a girl 5 min Dutusawit - 1. Our first time 52 sec Justhisonce - 3. Tense Victoria Nedveslyuk tries to relax before defloration 5 min Virgini18 - Exceptional teen bombshell has sex for the first time on camera 5 min Parabertasol - 6.
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But despite the modern tendency towards sexual freedom, even today there are vast differences in attitudes across the world, experts say. An informal global sex survey sponsored by the condom company Durex confirmed Buss' views. Just 3 percent of Americans polled called their sex lives "monotonous," compared to a sizable 26 percent of Indian respondents.
While 53 percent of Norwegians wanted more sex than they were having a respectable 98 times per year, on average81 percent of the Portuguese were quite happy with their national quota of times per year. Though poll numbers and surveys offer an interesting window into the sex lives of strangers, they're still constrained by the unwillingness of people to open up about a part of their lives that's usually kept behind closed doors.
And what if we weren't bound by such social limitations? Taylor offers the promiscuous-and very laid-back-bonobo chimpanzee as a utopian example.
Why Morning Sex Is the Best!
In physical terms, there is actually nothing that bonobos do that some humans do not sometimes do. Live Science.