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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, are intersex. {Wikipedia, Intersex}

Other chromosome combinations:



Intersex is a phenomenon in which one is not fully male or female, but rather a combination of both. It is not a belief, decision or a state of mind. Intersex is an actual 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 of intersex chromosomal/genetic changes, including:

  • 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.

Sometimes, certain people with intersex are called hermaphrodites, but that is colloquial, non-scientific use.  People who appear to have both male and female genitalia are actually almost always pseudo-hermaphoridtes:

* pseudo hermaphrodite – when one has, on the outside, both male and female reproductive organs. But (at most) only one set is fully functioning. (One can not impregnate itself)

True hermaphroditism is much rarer. Ovotesticular disorder of sex development. This is an intersex condition in which an individual is born with ovarian and testicular tissue. 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”)

Other genetic and chromosomal genders: Beyond male and female

Garden snail (Wikipedia)

Garden snail (Wikipedia)


This is a word generally not used often in science, because in the last century it has been used in different, contradictory ways. Note that none of these four definitions matches the other: each is completely different, thus rendering the word of no use, unless one first specifically notes the definition beforehand

  • 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)

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}

This is is new, evolving science, and diagnosing someone as transgender in any definite way does not yet fully exist.

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


In recent years this word has been used much more often, but it still has no agreed-upon, rigorous scientific definition.

Transgender refers to a person who feels that they are in a body not matching their perceived gender identity.

A clinical team can work with a person with to help determine one’s gender state through:

genetic analysis, chromosomal analysis, brain scans, and questionnaires (asking someone questions about what they feel)

When no cause is 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, a common condition affecting up to 2% of the population.

When a chromosomal or genetic cause is discerned, a clinical team may identify someone as being intersex.

Sometimes an individual identifying as transexual may not have any evidence of being intersex, yet in the judgement of a clinical team does not have gender dysphoria. In this latter case, someone is effectively pschologically intersex, with no (currently known) reason.

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

* make hypotheses with testable predictions

* read papers published in peer-reviewed scientific journals

* consider arguments based on scientific merit

* do not accept claims based on convenience, social norms, or peer-pressure.

* follow the scientific method, just as one does for questions in astronomy, evolution, physics, chemistry, etc.

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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