In biology, sex is a process of combining and mixing genetic traits, often resulting in the specialization of organisms into a male or female variety (known as a sex). Sexual reproduction involves combining specialized cells (gametes) to form offspring that inherit traits from both parents. Gametes can be identical in form and function (known as isogametes), but in many cases an asymmetry has evolved such that two sex-specific types of gametes (heterogametes) exist: male gametes are small, motile, and optimized to transport their genetic information over a distance, while female gametes are large, non-motile and contain the nutrients necessary for the early development of the young organism.An organism's sex is defined by the gametes it produces: males produce male gametes (spermatozoa, or sperm) 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 determination:The most basic sexual system is one in which all organisms are hermaphrodites, producing both male and female gametes—this is true of some animals (e.g. snails) and the majority of flowering plants. In many cases, however, specialization of sex has evolved such that some organisms produce only male or only female gametes. The biological cause for an organism developing into one sex or the other is called sex determination.
In the majority of species with sex specialization organisms are either male (producing only male gametes) or female (producing only female gametes). A few exceptions exist—for example, in the roundworm C. elegans the two sexes are hermaphrodite and male (a system called androdioecy).
Sometimes an organism's development is intermediate between male and female, a condition called intersex. Sometimes intersex individuals are called "hermaphrodite" but, unlike biological hermaphrodites, intersex individuals are unusual cases and are not typically fertile in both male and female aspects.
Human sexuality:Human sexuality is how people experience the erotic and express themselves as sexual beings. Frequently driven by the desire for sexual pleasure, human sexuality has biological, physical, and emotional aspects. Biologically, it refers to the reproductive mechanism as well as the basic biological drive that exists in all species and can encompass sexual intercourse and sexual contact in all its forms. Emotional aspects deal with the intense emotions relating to sexual acts and associated social bonds. Physical issues around sexuality range from purely medical considerations to concerns about the physiological or even psychological and sociological aspects of sexual behaviour.
The term can also cover cultural, political, legal and philosophical aspects. It may also refer to issues of morality, ethics, theology, spirituality or religion and how they relate to all things sexual. Recent studies on human sexuality have highlighted that sexual aspects are of major importance in building up personal identity and in the social evolution of individuals.
