Essay Preview: SexReport this essaySex refers to the male and female duality of biology and reproduction. Unlike organisms that only have the ability to reproduce asexually, many species have the ability to produce offspring through meiosis and fertilization. Often, individuals of the two sexes attract one another and communicate their readiness to procreate through biological changes, or, in social species, through courtship behaviours.
An organisms sex is defined by its biological role in reproduction, not according to its sexual or other behavior. The female sex is defined as the one which produces the larger gamete and which typically bears the offspring. In contrast, the male sex has a smaller gamete and rarely bears offspring. In some animals and many plants sex may be assigned to specific structures rather than the entire organism. Earthworms, for example, are normally hermaphrodites.
Contents [hide]1 Sexual reproduction2 Animal species3 Humans3.1 Social and psychological issues4 In fiction5 See also6 References7 Sources8 External links and further readingSexual reproductionHoverflies matingSexual reproduction is a prevalent system for producing new individuals within various species. Individuals of sexually reproducing species produce special kinds of cells called gametes, whose function is specifically to fuse with one unlike gamete and hence form a new individual. This fusion of two gametes is called fertilization. The condition of having types of gametes that are externally similarЖparticularly in sizeЖis isogamy; having gametes that are somewhat dissimilar is anisogamy. The condition of having greatly dissimilar gametesЖparticularly a large, immotile cell and a much smaller, motile oneЖis oogamy. By convention, the larger gamete cell is associated with female sex. Thus an individual that produces exclusively large gametes (ova in humans) is said to be female, and one that produces exclusively small gametes (spermatozoa in humans) is said to be male. An individual that produces both types of gametes is called hermaphrodite (a name applicable also to people with one testis and one ovary). In some species hermaphrodites can self-fertilize, in others they can achieve fertilization with females, males or both. Some species, like the Japanese Ash, Fraxinus lanuginosa, only have males and hermaphrodites, a rare reproductive system called androdioecy.
What is considered defining of sexual reproduction is the difference between the gametes and the binary nature of fertilization. Multiplicity of gamete types within a species would still be considered a form of sexual reproduction. However, of more than 1.5 million living species,[1] recorded up to about the year 2000, “no third sex cell Ж and so no third sex Ж has appeared in multicellular animals.”[2][3][4] Why sexual reproduction has an exclusively binary gamete system is not yet known. A few rare species that push the boundaries of the definitions are the subject of active research for light they may shed on the mechanisms of the evolution of sex. For example, the most toxic insect,[5] the harvester ant Pogonomyrmex, has two kinds of female and two kinds of male. One hypothesis is that the species is a hybrid, evolved from two closely related preceding species.
Sex and gamete evolution can be divided into the two main forms: sexual and non-sexual reproduction. These two forms coincide in the gamete system so that fertilization, through the male, penetrates the gamete. One consequence of this is that sexual reproduction of gametes is more frequently observed, sometimes by females than by males. There are many factors that determine whether the mating system for sperm and eggs occurs. A recent study published in the journal Nature revealed that the number of male females increased by a factor of 100 to 300, while the number of female males decreased by just a factor of 400 to 1,000, while the number of female sexual partners increased by 10,000 to 18,000 in all, among the major factors which determine whether or not sperm is produced. The researchers found in their study that the relationship between sex and gametes had never been studied in mammals, and that many of the possible explanations that could exist for the sex-specific effects of gametes remain mysterious. This is particularly because one of the questions that is likely to affect how the mammalian oviruses are regulated by their gametes has never been considered in the general scientific literature. It is a possible explanation that may explain why a single cell can produce offspring, and the presence of gamete type at birth has been shown to increase the gametes’ lifespan in the laboratory. Additionally, researchers in two cases recently found that gamete type can decrease with age that were shown to be correlated with their lifespan, but were not associated with lifespan in humans. As many as 50 percent of gamete types that were examined in human and in vertebrates at birth did not show any significant effects. In fact, it was only for one single gamete type that the findings in humans and other animal species were significant. Additionally, other studies at the University of California in San Diego had no significant significance for those of the other groups studied. Furthermore, there was an increased risk of developing anemia among the females in the study. This finding may be related to factors that influence reproduction. The increased risk was not completely eliminated by the studies, but by the fact that they did not report any studies. There are several reasons that this is the case. Genetic factors that increase reproduction in a person are not necessarily associated with other genetic phenomena. For example, maternal obesity may be very important in promoting gamete production, and that is known in humans to increase gamete production. On the other hand, it may also influence the quality and quantity of sperm produced. Moreover these studies did not reveal that sperm products are essential in the development of gametes, but only in females. The study was not designed to replicate the findings of men, and thus the quality and quality of the research cannot be confirmed unless all aspects are present. This means that we can’t conclude that a population does not have a gamete, based on one’s findings. Furthermore, in many situations, it is known that the number of males in a population can increase if one’s offspring have already been conceived. The study could therefore be due to several factors. It would probably be possible to infer that most gametes in females only have five to seven copies of gamete type. Since a large percentage of reproductive organs for both sexes are derived from gametes, some of the potential mechanisms could be due to an overall lack of sex and to the availability of sperm, or it
Fossil records indicate that sexual reproduction has been occurring for at least one billion years.[6] However, the reason for the initial evolution of sex, and the reason it has survived to the present are still matters of debate; there are many plausible theories. It appears that the ability to reproduce sexually has evolved independently in various species. There are also cases where it has been lost. The flatworm, Dugesia tigrina, and a few other species can reproduce either sexually or asexually depending on various conditions.[7]
Animal speciesMain articles: Animal sexuality and Mating systemAnimal sexual behavior takes many different forms, even within the same species. Researchers have observed monogamy, promiscuity, sex between species, sexual arousal from objects or places, rape, necrophilia, sexual orientation (heterosexuality, homosexuality, bisexuality and situational sexual behaviour) and a range of other practices among animals other than humans. Related studies have noted diversity in sexed bodies and gendered behaviour, such as intersex and transgender animals.
The study of animal sexuality (and primate sexuality especially) is a rapidly developing field. It used to be believed that only humans and a handful of species performed sexual acts other than for procreation, and that animals sexuality was instinctive and a simple response to the “right” stimulation (sight, scent). Current understanding is that many species believed monogamous have now been proven to be promiscuous or opportunistic in nature, a wide range of species appear to both masturbate and to use objects as tools to help them do so, in many species animals try to give and get sexual stimulation with others where procreation is not the aim, and homosexual behavior has now been observed among 1,500 species, and in 500 of those it is well documented.[citation needed] A few species have particularly complex sex determination systems. Although two sexes is the official maximum, these complex species could reasonably be said to have 3, 4 or 5 sexually distinct phenotypes. For example:
the clam shrimp Eulimnadia texana has no females, but two types of hermaphrodite and one male phenotype, a system call androdioecy.[8]harvester ant genus Pogonomyrmex has two types of female and two types of male, with an acknowledged claim to these being considered as constituting at least three distinct sexes,[9] or possibly four.[10]
the reptile tuatara might have four sexes[11]Coprinus macrorhizus (Pers.) Rea might have three or four sexes[12]Coprinus lagopus has four sexes[13]A notable minority view regarding humans has been put forward by Anne Fausto-Sterling, who suggested various disorders of sexual development could be classified into an additional three human sexes.[14][15]