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Concept Version 9
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Sex and Physiology

Sex is biologically determined based on chromosomes, hormones, gonads, internal reproductive anatomy, and external genitalia.

Learning Objective

  • Characterize the physiological differences among male, female, and intersex individuals and the controversies surrounding "corrective" surgery


Key Points

    • In humans, biological sex is determined by five factors present at birth: chromosomes, gonads, hormones, internal reproductive anatomy, and external genitalia.
    • Sex is typically divided into male, female, or intersex (i.e., having some combination of both male and female sex characteristics).
    • Due to the existence of multiple forms of intersex conditions (which are more prevalent than researchers once thought), many view sex as existing along a spectrum, rather than simply two mutually exclusive categories.
    • Intersex infants with ambiguous outer genitalia are often surgically "corrected" to more easily fit into a socially accepted sex category. Human-rights defenders argue that this is an oppressive practice on par with genital mutilation.

Terms

  • intersex

    A variation in biological sex characteristics including chromosomes, gonads, or genitals that do not allow an individual to be distinctly identified as male or female.

  • sex

    The distinguishing biological properties by which organisms are classified as female, male, or intersex.

  • gonad

    A sex organ that produces gametes; specifically, a testicle or an ovary.


Full Text

The Biology of Sex

"Sex" refers to physiological differences between male, female, and intersex bodies. A person's sex includes both primary sex characteristics (those that are related to the reproductive system) and secondary sex characteristics (those unrelated to the reproductive system, such as breasts and facial hair). In humans, biological sex is determined at birth, typically by doctors, through the observance of five factors:

  1. the presence or absence of a Y chromosome;  
  2. the type of gonads;
  3. the sex hormones;
  4. the internal reproductive anatomy (such as the uterus in females); and
  5. the external genitalia.

In humans, sex is typically divided into male, female, or intersex. Intersex, in humans and other animals, is a variation in sex characteristics (including chromosomes, gonads, or genitals) that does not allow an individual to be distinctly identified as male or female. Such variation may involve genital ambiguity and/or combinations of chromosomes other than XY (typically found in males) and XX (typically found in females). In addition to the most common XX and XY chromosomal sexes, there are several other possible combinations commonly known as intersex, such as Turner syndrome (XO), Triple X syndrome (XXX), Klinefelter syndrome (XXY), de la Chapelle syndrome (XX male), and Swyer syndrome (XY female). Due to the existence of multiple forms of intersex conditions (which are more prevalent than researchers once thought), many view sex as existing along a spectrum, rather than as simply two mutually exclusive categories. 

Intersex: The Debate Over "Corrective" Surgery

Intersex infants with ambiguous outer genitalia are often surgically "corrected" at birth so that they more easily conform to a socially accepted sex category. What is considered male, female, or even ambiguous is largely classified by society, and this kind of "corrective" surgery is a highly controversial topic.

Defenders of the surgery argue that it is necessary for individuals to be clearly identified as male or female in order for them to function socially. Many intersex individuals, however, argue that such a procedure is invasive and unnecessary. Some individuals may be raised as a certain gender (boy or girl) based on the sex (male or female) that was chosen for them at birth, but then identify with another gender later in life; some may even opt for sexual reassignment surgery later in life to align more truly with who they are. 

Research done in the late 20th century has led to a growing medical consensus that diverse intersex bodies are normal—if relatively rare—forms of human biology, and up to 1.7% of live births exhibit some degree of sexual ambiguity. Opponents of the practice of "corrective" surgery maintain that the presumed social benefits of such "normalizing" surgery do not outweigh the potential costs; they argue that the effort to "normalize" or "correct" an intersex condition to fit what society deems acceptable is both problematic and oppressive. Intersex advocates such as Anne Fausto-Sterling label surgery without consent as a form of genital mutilation, and argue that surgery on intersex babies should wait until the child can make an informed decision for themselves. Studies have revealed that surgical intervention can have drastic psychological effects, impact well-being and quality of life, and does not ensure a successful psychological outcome for the child. Specialists at the Intersex Clinic at University College London began to publish evidence in 2001 that indicated the harm that can arise as a result of inappropriate interventions, and advised minimizing the use of childhood surgical procedures.

The Declaration of Montreal was the first to demand prohibition of unnecessary post-birth surgery to reinforce gender assignment until a child is old enough to understand and give informed consent. This was detailed in the context of existing UN declarations and conventions under Principle 18 of the Yogyakarta Principles, which called on states to "take all necessary legislative, administrative and other measures to ensure that no child's body is irreversibly altered by medical procedures in an attempt to impose a gender identity without the full, free and informed consent of the child."

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