16.4: The Biology of Sex and Gender

From birth, children are assigned a gender and are socialized to conform to certain gender roles based on their biological sex. “Sex,” refers to physical or physiological differences between males, females, and intersex persons, including both their primary and secondary sex characteristics. “Gender,” on the other hand, refers to social or cultural distinctions associated with a given sex.

When babies are born, they are assigned a gender based on an assessment of their biological sex—male babies are assigned as boys, female babies are assigned as girls, and intersex babies are born with sex characteristics that do not fit the typical definitions for male or female bodies, and are usually relegated into one gender category or another. Scholars generally regard gender as a social construct, meaning that it doesn’t exist naturally but is instead a concept that is created by cultural and societal norms. From birth, children are socialized to conform to certain gender roles based on their biological sex and the gender to which they are assigned.[1]

Psychologists have long admitted that sex refers to biology – genes, hormones and genitalia, and that gender refers to the psychological experience of femininity or masculinity and the range in-between. The above discussion was about how much of this debate has played out as well as what queer theorists assert.

Biological psychologists have focused on the role that biology plays in this process. It is commonly known and understood that human prenatal development starts with one cell typically having 2 sex chromosomes – XX or XY, and therefore the presence of the Y chromosome will “determine” male development. I put determine in quotes because this is in fact far from the actual truth. It is hardly as if the Y chromosome has a penis on it! It is important to understand the full process of genital development in utero first in order to understand the tenuous nature of such binaries. Of course, we all start off at conception with a single cell – mostly with an XX or an XY situation. The Y chromosome contains an SRY gene which triggers a cascade of events that lead to male genitalia, and its absence leads to female genitalia. So female development is the default system so to speak. At the start of embryonic development, the embryo has undifferentiated gonads. It is the presence of the SRY gene that at about 6 weeks of pregnancy causes the production of testes determining factor, a chemical that leads to the undifferentiated gonads becoming testes. Testes produce testosterone which further the development of the testes, and also produce Mullerian inhibiting substance – a hormone that causes the female reproductive duct possibilities to be removed, and the Wolffian or male reproductive duct system to flourish and develop further. It is not until about 3 months in utero that the fetus develops external genitalia ie a penis (the testes don’t descend into the scrotal sac until later).

So as you may note there are several steps from a Y chromosome to a “normal” male. And there are several things that have to happen in that cascade for one or other extreme to develop. Could there be situations where one is born with possibly both sets of reproductive organs, none, or ambiguous genitalia? Certainly! Similarly, during any developmental stage there are many situations where a person's hormones may not fall strictly into well-defined "male" or "female" ranges, and notably a person need not be only "male" or "female" across their genes, hormones or genitals.

Intersex

At least 1 in every 1,000 conceptions results in a variation of chromosomal sex beyond the typical XX or XY sets. Some of these variations include XXX (Figure 13.3.2), XYY, XXY, or even a single X (Dreger, 1998).

Figure \(\PageIndex{1}\): 9 year old girl with Triple X Syndrome.

Some individuals with atypical sex chromosomes may have unusual physical characteristics, such as being taller than average, having a thick neck, or being sterile (unable to reproduce); but in many cases, these individuals have no cognitive, physical, or sexual issues (Wisniewski et al., 2000). These sex-linked chromosomal disorders are briefly described in the Table below.

Table \(\PageIndex{1}\): Sex-linked Chromosomal Disorders

Disorder	Sex Appearance & Fertility	Characteristics
Klinefelter Syndrome (XXY)	Male, may have some breast development (often infertile)	The Y chromosome stimulates the growth of male genitalia, but the additional X chromosome inhibits this development (may have low levels of testosterone).
Supermale Syndrome (XYY)	Male (usually normal fertility)	Few symptoms, which may include being taller than average, acne, and an increased risk of learning problems. Generally otherwise normal.
Triple X Syndrome (XXX)	Female (usually normal fertility)	May result in being taller than average, having learning difficulties, decreased muscle tone, seizures, and kidney problems.
Turner Syndrome (XO)	Female, but immature (infertile)	Affects cognitive functioning and sexual maturation; short stature may be noted.

The more common of these sex chromosome disorders are Turner Syndrome and Klinefelter Syndrome. Turner Syndrome occurs when one of the X chromosomes is missing or damaged and the resulting zygote has XO sex chromosomes. This occurs in 1 of every 2,500 live female births (Carroll, 2007) and affects the individual’s cognitive functioning and sexual maturation. The external genitalia appear normal, but breasts and ovaries do not develop fully and the woman does not menstruate. Turner’s syndrome also results in short stature and other physical characteristics, such as a webbed neck, shield-shaped thorax, and cardiac defects.

Klinefelter Syndrome (XXY) results when an extra X chromosome is present in the cells of a male and occurs in 1 out of 700 live male births. The Y chromosome stimulates the growth of male genitalia, but the additional X chromosome inhibits this development. An individual with Klinefelter Syndrome often has some breast development, wide hips, infertility (this is the most common cause of infertility in males), small testicular size, and low levels of testosterone (National Institutes of Health, 2019). Figure illustrates the symptoms of Klinefelter's syndrome on the left and a 29 year old male with Klinefelter`s syndrome who is undergoing testosterone treatment on the right. Regular testosterone injections can promote strength and facial hair growth, build a more muscular body type, increase sexual desire, and enlarge the testes.

Figure \(\PageIndex{1}\): Symptoms of Klinefelter's syndrome [left] and 29 year old male undergoing testosterone treatment [right].

Intersex is the term used to describe situations where a person’s anatomy does not fit neatly into the male or female categories. There are several situations where hormones are not produced or bodies do not respond to the hormones that are produced resulting in intersex conditions. The most common of these are CAH and androgen insensitivity syndrome.

It is beyond the scope of this chapter, and indeed this book, to address all of the details involved here (for some short really interesting talks I would suggest watching Emily Quinn's TedTalk and actually anything else she has uploaded or written) but it is my hope that this small introduction has made you realize that even the largest argument for binaries – that humans are biologically “intended to be” either male or female – is very far from fact.

Although male and female are the most typical biologically ordained poles of sexual identity, a vast number of gradations can be produced by normally occurring variations in the underlying hormonal control mechanisms that guide gender differentiation" (Panksepp, 2004, page 234). In humans, intersex individuals make up about two percent—more than 150 million people—of the world’s population (Blackless et al., 2000). There are dozens of conditions that can lead to intersex anatomical variations, such as Androgen Insensitivity Syndrome and Turner’s Syndrome (Lee et al., 2006). The term “syndrome” can be misleading; although intersex individuals may have physical limitations (e.g., about a third of Turner’s individuals have heart defects; Matura et al., 2007), they otherwise lead relatively normal intellectual, personal, and social lives. In any case, intersex individuals demonstrate the diverse variations of biological sex.

Attributions:

[1] Intersex by Wikipedia is licensed under CC BY-SA 3.0

Sexuality and Sex Development by Naomi Bahm and ASCCC OERI in Biological Psychology is licensed under mixed open licenses.