The very first display of sex determination begins in the indifferent gonads, these are part of an early vertebrate fetus that may develop into either testes or ovaries. The genetic makeup determines what the gonads develop into. The Y chromosome creates testes through the SRY gene, the lack of such creates ovaries.

Indifferent Gonads

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.

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

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.  

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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