Sexuality Portal

Sex 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 organism's 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.

  

Animal species

the clam shrimp Eulimnadia texana has no females, but two types of hermaphrodite and one male phenotype, a system call androdioecy.^[1]

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,^[2] or possibly four.^[3]

the reptile tuatara might have four sexes^[4]

Coprinus macrorhizus (Pers.) Rea might have three or four sexes^[5]

Coprinus lagopus has four sexes^[6]

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.^[7][8] Despite mainstream opposition, including the Intersex Society of North America, Fausto-Sterling and others still maintain this view in current publications.

Other species have exhibited evidence of 5 sexes^[9]

Humans

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See Human sexuality for information about sexual activities, sexual sensation, sexual gratification, and sexual intimacy between human beings

In humans, "sex" is often perceived as a dichotomous state or identity for most biological and social purposes - such that a person can only be female or male. But many factors, including one's biology, environment, psychology and social context, have a role in determining how a particular person, and those around them, view their sex. Although the table below shows common differences between males and females, many people do not correspond to "male" or "female" with regard to every criterion. Additionally, about 1 to 1.7 percent of human beings exhibit biological sexual ambiguity to the degree that they cannot be physically classified as exclusively male or female. This is known as intersex. A person with intersex may have biological characteristics of both the male and female sexes.

"Primary" sexual characteristics are typically present at birth and directly involved in reproduction. "Secondary" sexual characteristics typically develop later in life (usually during puberty) and are not directly involved in reproduction. Differences between the sexes are known as sexual dimorphism. At the biological level these differences are usually:

The relationship between the various levels of biological sexual differentiation is fairly well understood. Many of the biological levels are said to cause, or at least shape, the next level. For example, in most people, the presence of a Y chromosome causes the gonads to become testes, which produce hormones that cause the internal and external genitalia to become male, which in turn lead parents to assign 'male' as the sex of their child (assigned sex), and raise the child as a boy (gender of rearing). However, the degree to which biological and environmental factors contribute to the psychosocial aspects of sexual differentiation, and even the interrelationships between the various psychosocial aspects of differentiation, is less well understood as illustrated by the ongoing nature versus nurture debate. Unfortunately, because of a lack of focus on this area, studies may use data from research not designed to discern the role of sex. One sample of 432 papers publishing the results of gender-related genetics found that only 66.6% of them had set out to deal with the subject before conducting any research and 87.3% used unsound statistics.^[12]

Social and psychological issues

Evolution of sex

Human sexuality

List of gender names

Mammalian gestation

Sexual differentiation

Sexual dysfunction

Sex ratio

Sexual intercourse

Age of consent

References

1. ^ Evolution with three sexes. University of British Columbia. Retrieved on 2007-01-03.
2. ^ G. E. Julian, J. H. Fewell, J. Gadau, R. A. Johnson, D. Larrabee (2002). "Genetic determination of the queen caste in an ant hybrid zone". Proceedings of the National Academy of Sciences 99 (12): 8157-8160. 
3. ^ Whitfield, John (2004). "Everything You Always Wanted to Know about Sexes". Public Library of Science: Biology 2 (6). 
4. ^ Tuatara
5. ^ Observations on Inheritance in Coprinus macrorhizus (Pers.) Rea
6. ^ The Pycnidia of the Rust Fungi
7. ^ The Five Sexes Revisited, Sciences, Jul/Aug2000, Vol. 40 Issue 4, p18, 6p, 1c, 2bw
8. ^ Two Sexes Are Not Enough
9. ^ Cytoplasmic Fusion and the Nature of Sexes
10. ^ "thickens the brow and upper bridge of the nose" [1]
11. ^ [2], [3]
12. ^ Nikolaos A. Patsopoulos, et al. (Aug 2007). "Claims of sex Differences: An empirical assessment in genetic associations". J. Am. Med. Assoc. 298 (8): 880-893. 

1. http://www.columbia.edu/itc/hs/pubhealth/modules/reproductiveHealth/anatomy.html
2. http://www.humanhormones.com/category/steroids/androgens/
3. http://www.bbc.co.uk/science/humanbody/sex/articles/testosterone.shtml
4. http://www.sciencedaily.com/releases/2007/05/070523105948.htm

External links and further reading

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• Francoeur, Robert T. (ed.), The International Encyclopedia of Sexuality [full text]
• Janssen, D. F., Growing Up Sexually. Volume I. World Reference Atlas [full text]
• Francoeur, Robert T. and Rayond J. Noonan, (eds.) "Continuum Complete International Encyclopedia of Sexuality". Continuum, August 2003,
• Human Sexual Differentiation by P. C. Sizonenko
• New Scientist article on Sex chromosomes in the platypus
• Human Sexuality Info by University of California Santa Barbara

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