Gender, as described by theorists and activists as an expression of behavior, is practically “personality” at this point.

Are there personality sex differences? Yes. Does this mean a masculine girl is actually a boy? No.
This is what a typical sex difference between males and females in a Big Five personality trait looks like. The averages are very close together.

Traits like this show us there is plenty of variation within males and within females to reject rigid behavioral categorizations.
Trait Agreeableness.

Males and females, on average, are far more alike than different in this trait.

Extremes of the bell curves show little overlap, however (Ex: The MOST disagreeable people are almost always men.)

Males and females, on average, are moderately different on this trait but share considerable overlap as well.
Vocal pitch.

Little to no overlap, on average, between men and women.
Grip strength.

Not much overlap at all, but many outliers.

Males are more variable.
What all this shows us is that, no matter what trait we study (for the most part), there will be plenty of variation within males and within females.

The sexes as reproductive categories are simple and binary. The trait variation of physiology and behavior within is not.
This means that for every masculine male and feminine female, there will be plenty of feminine males and masculine females depending upon the extent of the variation in the trait being studied.

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More from @zaelefty

18 Oct
Across species, it does not matter whether male and female exist in the same individual (hermaphroditism) or in separate individuals (gonochory); sex is binary in any species that has male and female reproductive functions.
For example, in sunflowers, like many other flowering plants, individuals are both male and female, and so the species is hermaphroditic.

In humans, like all other mammals, individuals are either male or female throughout their life cycle, and so the species is gonochoric.
Sex in the sunflower and sex in humans requires only two roles: a male and female, and so sex is binary in both species.
Read 10 tweets
15 Oct
2020 paper on sex differences in gene expression across human tissues.

"Human development, physiology, and disease manifest differently in males and females ... We find sex-biased regulatory network structures in each tissue."…
"Even though most transcription factors (TFs) are not differentially expressed between males and females, many have sex-biased regulatory targeting patterns...
Genes that are differentially targeted by TFs between the sexes are enriched for tissue-related functions and diseases."
"Our systems-based analysis identifies a repertoire of TFs that play important roles in sex-specific architecture of gene regulatory networks, and it underlines sex-specific regulatory processes in both health and disease."
Read 5 tweets
14 Oct
“If there is any trait overlap between two categories, then those two categories must be social constructs.”

Males and females overlap significantly in Big Five personality traits and height, among many other things.

Does this mean the categories of male and female are not real?
Humans share large portions of their genome with many other animals. Does this mean humans are not real?
Read 4 tweets
12 Oct
It’s actually the inverse: The dual idea of sex is reinforced when examining numerous other species.

Almost all complex species utilize male and female reproductive functions, whether they are composed in the same individual or in separate individuals.
Find the third reproductive function in anisogamous species, and I’ll change my mind 🤓
Scharer, L. (2017). The varied ways of being male and female. Molecular Reproduction & Development, 84.
Read 4 tweets
10 Oct
We do not need to see gametes being produced to identify sex. Like any other biological system, 'sexes' are identified by their structure and function.

Their structures comprise the reproductive organs; their function is to produce gametes.
Just like sexes, eyes are identified by their function and structure.

Their structures comprise a unique set of components (cornea, iris, pupil, lens, retina, macula, optic nerve, choroid and vitreous); their function is to produce sight.
Lack of sight does not mean one has no eyes, and lack of gamete production does not mean one has no sex.

The material biological systems do not suddenly disappear when their function is absent.
Read 6 tweets
4 Oct
Identifying a biological system requires two things:

1) Material of the system.
2) The effect it serves.

For example, eyes are not only defined through their material composition but also through the effect it gives to the organism (being able to see).
This applies to all types of biological systems, including sexes.

Sexes are defined as “the phenotype that produces [X] gametes.”

The definition of sexes meets the two criteria. It identifies the material composition (phenotype) and the effect it serves (production of gametes).
Activists like to claim that recognizing the function of a system in biology is akin to ascribing teleological purpose to it.

But there is a difference between identifying a bio system through its effects versus claiming that a system only exists *because* of its function.
Read 7 tweets

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