Most individuals are either biologically male or female which corresponds to chromosomes, external genitalia, internal reproductive structures, etc.. However, there are a number of exceptions possible, for example intersex presentation and genetic conditions. This makes sex an unreliable source to be the basis of gender. 

Looking at behavior, it is difficult to differentiate any action as either masculine or feminine. The only action exclusive to one sex is childbearing and birth. There may be more common actions found in one sex or the other but almost all individuals display some of these behaviors regardless of sex.

Behavior

There is evidence that DHT, the androgen that masculinizes genitalia, may also masculinize the brain, affecting behavior. There are structural sex differences in brains, including possible masculine and feminine brain regions. This means that individuals cannot simply be feminine or masculine, the structure or behavior must be specified.

Brain Structures

Sexual orientation refers to what gender(s) an individual is attracted to. However, there are more sexual orientations than just being heterosexual, including a number that involve being attracted to member of the same gender as the individual. With the varying attractions, this is also not an indicator as to what gender an individual is.

Sexual Orientation

There are a number of possible ways to define gender, this includes:

 • Biologically (sex)

 • Non-biological sources (behavior or brain structures)

 • Sexual Orientation

However, it will be shown that none of these options are satisfactory enough as a definition and that they are all distinct and independent from one another.  

Rutgers University

The process of how embryos develop into either male or female bodies and behaviors. The process begins while in utero in mammals, but continues well into adulthood. Despite physical appearance, people may be masculine, feminine, or a blend of the two sexes.


Sexual Differentiation

Breedlove, S. & Watson, N. (2017). Behavioral neuroscience, eighth edition. Oxford University Press.

Behavioral Neuroscience 8th Edition

Sex determination is the initial decision for a fetus to develop into a characteristically male or female body. For the most part, if the father's gamete contains a Y chromosome, the embryo develops male, and if it contains a X chromosome, it would develop female. Mothers only have X chromosomes so the determination is determined by the father.

Sex Determination

How to Define Gender

Gonadal hormones drive sexual differentiation; the presence of testosterone promotes masculine physical development, whereas the absence of testicular hormones leads to feminine development. Furthermore, evidence suggests that these hormones influence brain development in a similar manner.

Gonadal Hormones

The fact that female and males in most species behave differently implies that something in the brain development is different. What is in question is did this difference occur because of prenatal steroid exposure or from social influence.

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