Biological Sex

Biological sex includes all those purely biological characteristics that allow us to classify an individual’s sex as female or male.
However, we will see how these characteristics do not always allow for a binary definition of sex (i.e., female or male). Sometimes, these characteristics lead to being “somewhere in between the two sexes,” which brings us to the concept of intersexuality.

Let’s make things a little more complex (but not too much).
Biological sex includes:

• Genetic characteristics
• Gonadal and hormonal characteristics
• Phenotypic characteristics

These characteristics, as mentioned, allow for the classification of an individual's sex.

In the previous post, we saw how sex chromosomes define genetic sex. The XX pair is attributed to the female sex, and the XY pair is attributed to the male sex.
However, we also saw that there are situations where chromosomes do not pair in this way, resulting in intermediate cases.

Gonads are glands responsible for producing gametes and sex hormones. Female gonads are the ovaries, and male gonads are the testicles.
Gametes are the cells involved in reproduction: eggs in females and sperm in males.

Sex hormones regulate biological characteristics such as the functioning and morphology of the genitals and other typically sexual structures (like breasts, body hair, and fat distribution).
The main sex hormones are estrogens and testosterone. Estrogens are produced in higher quantities in women, while testosterone is produced more in men.

Phenotype refers to the visible physical traits of an individual and is the result of gene expression. For example, we may carry the gene for blue eyes, and others see our beautiful blue eyes.
Sexual phenotype is divided into primary and secondary sexual characteristics.

• Primary sexual characteristics are the organs involved in reproduction. Simply put: in women, these include the vagina and ovaries; in men, the penis and testicles.
• Secondary sexual characteristics are all physical differences between the sexes that appear during puberty and develop during adolescence. In women, these include breast development, widening of the hips, onset of menstruation, etc. In men, body hair, muscle growth, and the development of the Adam's apple, etc.

The development of a binary sexual phenotype (female or male) is the result of hormonal balance.
However, we’ve seen that women produce testosterone (a male hormone), and men produce estrogens (female hormones).
When this balance doesn’t follow the typical path, the sexual phenotype may differ from the binary model and instead be intersex.

Intersexuality is therefore a situation in which the genetic, gonadal, and hormonal sex do not lead to a phenotype that can be classified as typically female or typically male.

Sources:

• Pinel, J.P.J. & Barnes, S.J. (2018) – Biopsychology

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