Sex ratio

The sex ratio is the ratio of males to females in a population. In most sexually reproducing species, the ratio tends to be close to 1:1. Reasons for the tendency are discussed in Fisher's principle. For various reasons however many species deviate from anything like an even sex ratio, either periodically or permanently. Examples include parthenogenic species, periodically mating organisms such as aphids, some eusocial wasps such as Polistes fuscatus and Polistes exclamans, bees, ants, and termites.

The human sex ratio is of particular interest to anthropologists and demographers. In human societies, however, sex ratios at birth may be considerably skewed by factors such as the age of mother at birth, and by sex-selective abortion and infanticide. Exposure to pesticides and other environmental contaminants may be a significant contributing factor as well. As of 2014, the global sex ratio at birth is estimated at 107 boys to 100 girls (1000 boys per 934 girls).

Types

In most species, the sex ratio varies according to the age profile of the population.

Sex

Organisms of many species are specialized into male and female varieties, each known as a sex.Sexual reproduction involves the combining and mixing of genetic traits: specialized cells known as gametes combine to form offspring that inherit traits from each parent. Gametes can be identical in form and function (known as isogamy), but in many cases an asymmetry has evolved such that two sex-specific types of gametes (heterogametes) exist (known as anisogamy).

Among humans and other mammals, males typically carry XY chromosomes, whereas females typically carry XX chromosomes, which are a part of the XY sex-determination system. Other animals have a sex-determination system as well, such as the ZW sex-determination system in birds, and the X0 sex-determination system in insects.

The gametes produced by an organism are determined by its sex: males produce male gametes (spermatozoa, or sperm, in animals; pollen in plants) while females produce female gametes (ova, or egg cells); individual organisms which produce both male and female gametes are termed hermaphroditic. Frequently, physical differences are associated with the different sexes of an organism; these sexual dimorphisms can reflect the different reproductive pressures the sexes experience.

Sex (film)

Sex is a 1920 American silent drama film directed by Fred Niblo, written by C. Gardner Sullivan, produced by J. Parker Read, and starring Louise Glaum. On its surface, the film was a morality story on the evils of marital infidelity. However, the film's producer, J. Parker Read, had made a series of pictures on sex themes. The release of Sex, with its provocative title and explicit scenes of seduction and debauchery, made it the subject of controversy among censors and commentators.

Plot

The film is a morality story on the evils of marital infidelity and the wild lifestyle of New York actors. At the same time, the film included scenes of seduction and debauchery that made it the subject of controversy over its prurient content.

The film's plot centers on Adrienne Renault (played by Louise Glaum), the beautiful queen of the Midnight Follies at the Frivolity Theater.

The film opens with Renault's current conquest, a married millionaire, Philip Overman (played by William Conklin). Overman is in his private box watching Renault perform her seductive "Spider Dance." Renault comes on stage dressed as a spider, "clad in a translucent cloak of webs wrapped cloak-like around a body-hugging black sheath."

Sexual intercourse

Sexual intercourse, or coitus or copulation, is principally the insertion and thrusting of the penis, usually when erect, into the vagina for sexual pleasure, reproduction, or both. This is also known as vaginal intercourse or vaginal sex. Other forms of penetrative sexual intercourse include anal sex (penetration of the anus by the penis), oral sex (penetration of the mouth by the penis or oral penetration of the female genitalia), fingering (sexual penetration by the fingers), and penetration by use of a dildo (especially a strap-on dildo). These activities involve physical intimacy between two or more individuals and are usually used among humans solely for physical or emotional pleasure and commonly contribute to human bonding.

A variety of views concern what constitutes sexual intercourse or other sexual activity, which can also impact views on sexual health. Although the term sexual intercourse, particularly the variant coitus, generally denotes penile-vaginal penetration and the possibility of creating offspring, it also commonly denotes penetrative oral sex and penile-anal sex, particularly the latter. It is usually defined by sexual penetration, while non-penetrative sex acts, such as non-penetrative forms of cunnilingus or mutual masturbation, have been termed outercourse. Non-penetrative sex acts, however, may additionally be considered sexual intercourse. The term sex, often a shorthand for sexual intercourse, can mean any form of sexual activity. Because people can be at risk of contracting sexually transmitted infections during sexual activities, though the transmission risk is significantly reduced during non-penetrative sex,safe sex practices are advised.