This post was co-authored by Frederick L. Coolidge¹ and Apeksha Srivastava.²

¹Professor, University of Colorado, Colorado Springs, USA

²Doctoral Candidate, Indian Institute of Technology Gandhinagar, India

It is part 1 of a 3-part series.

Overview

Many recent editorialists, particularly in regard to trans women (MTW) and trans men (WTM), have noted that a trans woman still possesses XY chromosomes and a trans man still possesses XX chromosomes. These same editorialists subsequently castigate trans people for presenting or identifying themselves as women or men. One major problem with their arguments is that they are conflating or misconstruing the scientific terms of sex, gender, and sexual preference and their individual heritable bases. The purpose of this series of articles is to delineate the three terms and provide a clearer basis for their use.

Definition

The term sex refers to one’s biological genitalia at birth (e.g., penis or vagina) and the reproductive organs associated with them (e.g., testicles, ovaries, etc.). The term gender refers to one’s presentation or identification with the cultural stereotypic behaviors of a man, woman, both, or neither. The term sexual preference (synonymous with sexual orientation) refers to the expressions of one’s predilections or sexual desires.

Part 1: Sex

A person’s biological sex is determined by genes that are heritable biological or chemical units, which are segments of DNA. DNA can be considered a blueprint for an organism’s physical nature and behaviors. Each cell in the human body contains 23 pairs of chromosomes, which are “threads” of gene sequences. Sperm cells in men and egg cells in women are exceptions to this pairing, as they contain only 23 single chromosomes.

The cells of the human body also vary in kind: Skin cells differ from nerve cells, which differ from eye cells, etc. These differences are accounted for by the many genes that are located along the chromosomes. Thus, the genes are responsible not only for the different structures of cells and groups of cells (e.g., penis, vagina, ovaries, testicles, eyes, toes, brain, etc.) but also for behavioral traits (e.g., aggression, extraversion, introversion, etc.). It is also important to note that one’s biology interacts with one’s environment. For example, naturally aggressive people can become more or less aggressive in particular environments.

In the 1800s–1900s, it was discovered that the 23 pairs of chromosomes in women were similar in length and gene position (i.e., homologous), and each pair was joined near the center (centromere), forming an “X” shape. However, in men, one pair was not homologous because one chromosome was “X” shaped, and the other was “Y” shaped, as if missing a leg. It was quickly surmised that this pair, arbitrarily labeled the 23rd pair, also called the sex chromosome, was responsible for a person’s genitalia and reproductive organs. Hence, the “XX” shape is associated with being a woman (at least, in biological structure), and the “XY” shape is associated with being a man. One’s sex assignment is made at birth based on a simple examination of a baby’s external genitalia. Thus, the term "sex" is synonymous with biological sex, natal sex, or sex assigned at birth.

After a man’s sperm fertilizes a woman’s egg, this cell (zygote) begins replicating in great numbers, ultimately creating a fetus, then a baby, later followed by an adult human body. However, in the replication process, although amazingly accurate, there may be errors, called "mutations". The word mutation has a negative connotation, but it comes from the Latin word mutatus, meaning change. Mutations can be caused by the replication process itself or the external environment, like ultraviolet light, drugs like thalidomide, etc.

There Is More to Life Than XX and XY

In addition to the chromosomal options of XX and XY, mutations in the 23^rd chromosome set may also make them XXY (Klinefelter syndrome), XYY, a single X (known as XO or Turner syndrome), or XXX (Triple X syndrome). Some humans may also be categorized as intersex, which could be a combination of male and female biological structures (for example, a person who is male-assigned at birth but internally possesses ovaries); there are multiple categories of intersex.

As noted earlier, some have argued that surgically altering one’s genitalia does not change their XX, XY, XXY, XYY, X, XXX, etc. chromosomal structures, which is true. However, this argument ignores the strong genetic influences on one’s gender preference. It is important to remember that sex assigned at birth and gender are different terms, and each has a heritable basis. Claims that all XX or XY people should act like women or men because of this chromosomal basis is an affront to the science of sex and gender and misses the scientific evidence that there is a difference between sex and gender and their biological heritabilities.