Saturday, April 25, 2015

A crash course in sex, gender and sexual identity: Part One.

The recent furor (in some circles) over Chris Jenner has clarified for me some of the main misconceptions about transgender identity.

 Today, I'd like to start a series of post on the biological basis of sex and gender, move in to some basic logical assumptions from these biological realities, and end with what I believe some "next steps" are.  Oh, and probably go into a side-note on sexual identity since it ties  in as well.

 (For the curious, I'm a heterosexual cis-woman.  I'm not going to pretend I understand what it's like being transgendered.  I do know that change happens through both the bravery of the oppressed in society AND through the privileged groups in society challenging other members of the privileged group on hurtful and false beliefs.)

Problem number one: People use linguistic shortcuts that lead to massive confusion.

Bloggers keep using the terms "sex" and "gender" interchangeably and with far too wide a definition. 

Here are some biological / psychological terms used to better discuss the ideas that comprise "sex" and "gender".

Physical Sex: The definition of "sex" in this case describes the reproductive system especially the secondary sex characteristics of a person.  Humans have an instinctive ability to class other humans into two groups.  Humans who develop breasts, hips and little body hair are "female".  Humans who develop facial/body hair, increased muscle mass, and a deepened voice are "male".  This division has been found in all cultures throughout history and can be extremely difficult to circumvent in psychological experiments. 
For example, imagine two groups of people of different races and sex all dressed in white t-shirts and jeans.  One group makes statements that are "conservative" in nature.  The other group makes "liberal" statements.  Since both groups are wearing identical clothing, people will misremember quotes by gender (confusing one woman with another) and race (confusing one Caucasian with another) regardless of the side.  If you put the two sides in different colored t-shirts, the misremembering quotes by race nearly disappears while misremembering by gender stays constant.  From this, psychologists and evolutionary biologists believe that identifying humans by sex is biologically programmed.  In other words, babies are born with a script in their brains that says "Females look like this.  Males look like that."

Notice that this has nothing to do with cultural cues or expectations.  This is simply a decision about which of two binary categories ("female" or "male") a person falls into based on physical characteristics.

Using a binary system for physical sex has one big problem: some people are born with indeterminate external genitals.  This can happen because there are several different hormonal cascades and anatomical processes going on mostly independently of each other to form different parts of the internal and external reproductive systems during the first weeks of gestation.  If the fetal cells don't produce enough hormones, are exposed to the wrong hormone, or the cells are missing receptors to recognize the hormones, a reproductive system can form that is neither entirely female or entirely male.  (My high school kiddos were always curious is a person could develop an intact female and an intact male reproductive system.  The short answer: No.   The primordial gonads become ovaries OR testes. This is hormonally regulated and determinate so a dose of estrogen makes the tissue "become" female or a dose of testosterone makes the tissue "become" male.)  The best advice I've heard for parents who have a kid whose physical sex is not clear at birth - make a best guess from the doctor's advice on which physical sex the kid is, use the pronouns that match that physical sex, and be willing to change those pronouns when the kid is old enough to tell you what gender they are.

Genotypic Sex: This one has been tripping bloggers up left and right.  In humans, all living people have at least 1 X chromosome.  This is because the X chromosome has genes on it that are required for life and completely unrelated to the reproductive system.  For example, the X-chromosome has genes that control blood clotting and immune system regulation.  Some people have two or more X chromosomes. 

These people can be either male or female. 

See, the X chromosome doesn't do a ton in terms of sexual development.  In humans, the default sex that develops during the embryonic period is female through a built-in set of genetic instruction.

Humans without a Y chromosome will develop into a human with a female sex.

Now, the Y chromosome is different.  To start with, it's a ton smaller than the X chromosome and only carries a handful of active genes.  One of those genes (SRY) triggers male sexual development during the embryonic period.    SRY sets off a different set of chemical cascades that stops female reproductive development and promotes male sexual development.

Most people with a Y chromosome will develop into a human with a male sex.   But not all.

There are people who are of the female sex who have XY genotype.  This is caused by an allele on the X chromosome that blocks the effect of testosterone on fetal development. 

Plus, the sex chromosomes (X and Y) are the only pair in the human body that can be silenced (or turned off) when there are multiple copies.  This is standard operating procedure in XX humans; one of the two X chromosomes is randomly silenced in each cell.  This is also why calico cats are generally female - each colored orange or black patch of fur is caused by the silencing of one X gene while the white comes from a complicated interaction of genes.)  The Y gene is pretty near silent after the first few weeks of gestation.

Why did I bring that up?  Well, like all of biology, genotypic sex is more complicated than XX and XY.  You can have XO (only one copy of an X), or XXX or XXY or XYY or XXYY....the list goes on, and on and on.  Of all of these genotypes, only XO (Turner's syndrome) gives changes that are visible - and really only visible if you've studied about it.  We don't really know how many people are walking around with sexual genotypes other than XX, XY and XO. 

So,  when anyone tells you that Chris Jenner is XY in all of his cells, the only logical response is to ask how they saw his karyotype - the process of visualizing all of the chromosomes in a cell.  It's the only way to find out what genetic sex a person is.

Important take-aways:
  • Physical sex refers to which secondary sex characteristics a person has.  The binary nature of the system creates problems when someone has a reproductive system that is not fully female or male.
  • Genetic Sex refers to the compliment of sex chromosomes (X and Y) present in a person.  Ususally, a someone with a female physical sex is XX and a male physical sex is XY - but this cannot be determined without medical testing AND is not always true.
  • Our sexual characteristics are determined by hormonal cascades during early embryonic development.  These cascade generally produce female and male people, but can "misfire" and create individuals that have incomplete reproductive systems.
In my next post, I'll look at how "gender" and "gender identity" are different from physical sex and genetic sex.


  1. Excellent primer - if memory serves, I seem to recall that in general, people with genotypes with an odd number of X's generally have fewer issues; the majority of the issues seem to occur when there are an even number of X's along with a Y - does that fit what you've seen or no?

  2. Good post, but did you actually mean Chris Jenner, or did you intend her former spouse, now Caitlyn Jenner?

    1. I did. I screwed it up and decided to leave it for people to enjoy chuckling at. To be fair, I'm horrible at names in real-life, so my online persona matches my off-line self :-P