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Sex and gender (human)


Biological sex is determined by five factors present at birth:

  • the type of gonads—ovaries or testicles;

  • the internal reproductive anatomy (such as the uterus in females); and

  • the external genitalia.

Most people are either male or female.

People whose characteristics are not either all typically male, or all typically female, due to chromosomal changes are intersex. {Wikipedia, Intersex}

Gender, how one perceives one’s sex, is a topic that one studies with science. We have learned that the following factors affect a person’s gender identity.

Gender Identity Prenatal and postnatal factors



Intersex is a phenomenon in which one is not fully male or female, but rather a combination of both.

Intersex is not a belief or choice. It is an actual, significant biological difference, caused by:

  • error in chromosome sorting (an extra X or Y chromosome, or a missing X or Y chromosome)

  • damage to a chromosome, causing a piece of a male chromosome to stick to a female chromosome (or vice-versa) damage to one or more genes on a chromosome, which affects gender:

For example, lacking the enzyme needed to convert testosterone to dihydrotestosterone (DHT).

There are wide variety of results:

  • male genitals on outside, female ovaries inside

  • female genital outside, testes inside

  • mild to major changes in the shape of genitals.
    The person’s gender often can not be determined by looking at the resulting genitals.
    A child born with genitalia atypical enough to call in an expert occurs in about 1 of 1,500 births

  • changes to neural development of the brain, so that a person may feel one gender, while their external genitalia presents as another

Intersex children may be surgically and/or hormonal altered to fit into what appears to be their dominant gender. However, medical science recommends not doing this until well after a child goes through puberty. Only several years after this does a child’s psychological experience of gender become more stable.

Research indicate that intersex bodies are normal—although very rare—forms of human biology.

Intersex people have various gender identities. Most identify as either a woman or man. Some may be raised as a certain sex, but then after puberty, identify with another gender.

Intersexual people are not hermaphrodites. That term is only used for animals which have both complete and fully-functioning, natural male and female organs. This condition is quite rare. Out of 7 billion people, only 10 people are currently diagnosed as having this condition (“True Hermaphroditism and Mixed Gonadal Dysgenesis in Young Children: A Clinicopathologic Study of 10 Cases”, Mod Pathol. 2002 Oct;15)

See our article on Other genetic and chromosomal genders: Beyond male and female


This word is generally not used often in science, because it is used in different, contradictory ways. For instance:

  • a straight heterosexual male, who cross-dresses
  • a euphemism for intersex
  • a person who psychologically feels that they belong to the opposite sex – with no diagnosable reason.
  • a person who is chromosomally male, genetically male, and physically male (appearance and genitalia), and who psychologically feels that they belong to the opposite sex, and they do have a diagnosable reason (e.g. brain scans, see below)
  • a person who is chromosomally female, genetically female, and physically female (appearance and genitalia), and who psychologically feels that they belong to the opposite sex, and they do have a diagnosable reason (e.g. brain scans, see below)

Example of a specific, scientific use of this term:

Androphilic male-to-female transsexuals. Appear male externally, but by puberty identify as female. Some studies show that these men have some brain structures more like women than men:

Gynephilic female-to-male transsexuals. Appear female externally, but by puberty identify as male. Some studies show that these women have some brain structures more like men, than women. {Wikipdia, transgender}


In recent years this word has been used much more often, but it still has no specific, rigorous scientific definition. Loosely defined, the term refers to a person who feels that they are in a body not matching their perceived gender identity.

If one feels this way, a clinical team can assist. People who consider gender transitions can ask scientific questions that can be answered with  genetic analysis, chromosomal analysis, brain scans, and questionnaires.

When no cause for such feelings are discerned, a clinical team may identify someone as having gender dysphoria/gender identity disorder. This is a psychological condition in which one is intensely uncomfortable with their gender. There are many forms of body dysmorphia, affecting up to 2% of the population.

Note: When a specific chromosomal or genetic cause is discerned, a clinical team may identify someone as being intersex, not transgender.

There is no specific, scientific test to show that one is transgender. There is some suggestive science that implies such tests may be possible. See “Is There Something Unique about the Transgender Brain?” Imaging studies and other research suggest that there is a biological basis for transgender identity. By Francine Russo, Scientific American, January 1, 2016

Is There Something Unique about the Transgender Brain? Scientific American

There unfortunately are social controversies over this issue. My hope is that students will study the issue the same way they approach all scientific questions:

* make hypotheses with testable predictions.

* read papers from peer-reviewed scientific journals.

* do not accept claims based on social, political or group pressure.

Other genetic and chromosomal genders: Beyond male and female

Also, see Controversies

Vincenzo Galilei, father of Galileo.

Vincenzo Galilei, father of Galileo.


A Practical Approach to Intersex, M. David Bomalaski, Urol Nurs. 2005;25(1):11-18, 23-24.

Should We ‘Fix’ Intersex Children? Standard medical practice is often to operate to “normalize” genitals, but some families are fighting back. Charlotte Greenfield, July 8, 2014, The Atlantic

Science In School: European Journal for Science Teachers
Intersex: falling outside the norm, Nina Notman, Issue 23 – 22/05/2012

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