MALES-FEMALES

Photo of a male hominin and a female hominin, pre-humans about 6 millions years ago

All mammals are (and always have been) either male or female

Mammals evolved about 180 million years ago.
There were (and are) two sexes of mammals: male and female.

All primates were and are either male or female

Primates evolved about 55 million years ago.
There were (and are) two sexes of primates: .male and female.

All monkeys - the "cousins" of humans - were and are either male or female

Monkeys - our closest living relative - evolved about 30 million years ago.
There were (and are) two sexes of primates: male and female.

All hominins - the predecessors of humans - were either male or female

Hominins, the direct ancestor of humans (aka homo sapiens) evolved about 6 million years ago.
There were two sexes of hominins: male and female.
Pictured above are a male and a female homo habilis, a hominin ancestor of humans.

Photo of a pre-historic (350,000 years ago) man and woman and their young child

The differences between males and females have allowed our species to continue

for 300,000 years...
The primary function of female humans (women) is to bear children and nourish their young with the breastmilk their body creates.
The primary responsibility of male humans (men) is to protect women and children. Historically, men were primarily responsible for securing food, particularly animal protein.
It is only fairly recently that women have worked outside of the home, hired others to care for their young and secured their own food.

Sex is determineD by sex chromosomes

SEX CHROMOSOMES

The X sex chromosome is needed for all human, all primate, and all mammalian life.
The Y sex chromosome started as a mutation from the X sex chromosome roughly 180 million years ago.
The X sex chromosome contains over 1000 genes, while the Y sex chromosome (because it is a mutation of the X sex chromosome) contains only ~ 20.

SEX (MALE AND FEMALE)

At conception, a human - like all other mammals - receives one sex chromosome from their mother (always an X) and one sex chromosome from their father (either an X or a Y).
In humans - like in all other mammals, the Y sex chromosome distinguishes males from females at the genetic level:
If a human has XX sex chromosomes then she is a female and has female sex characteristics (vagina, uterus, fallopian tubes, clitoris, cervix, and the ability to menstruate, give birth, and breast feed when matured).*
If a human has XY sex chromosomes then he is a male and has male sex characteristics (e.g., a penis, scrotum and the ability to impregnate a women when matured).*

* Sex anomalies are the exceptions to the "XX-XY Rule."

Sex anomalies are extremely rare.
Some refer to some of these sex anomalies as Disorders of Sexual Development (DSDs).
However, anomalies of the "XX-XY Rule" often affect more than the just the reproductive systems, although that is often a key feature of any particular sex anomaly.

Image of male and female reproductive systems with parts labeled

The male reproductive system includes the testes (which produce sperm), penis, epididymis, vas deferens, ejaculatory ducts and urethra.
The female reproductive system consists of the internal female sex organs including the ovaries (which produce eggs or oocytes), fallopian tubes, uterus, cervix, vagina and the external female genitalia, or vulva As a female matures, the glandular tissue in her breasts become able to produce breast milk for nourish children - whether or not she has given birth. Induced lactation is also known as "adoptive breastfeeding."

Male and female humans differ in bone structure and muscles

Compared to women, men have more robust skeletons

Males tend to have a larger and more robust skeleton with greater bone development at muscle attachment sites.

Male and female pelvic bones differ

The pelvic bones of males and females differ because women birth children and men do not.

Men have more muscle than women

Compared to women, men have more muscle mass and less body fat than women.
Women require more body fat for procreation and breast feeding offspring.
While a man only needs 3% body fat, a woman needs at least 12%. Moreover, unless she has at least 18% body fat, she may have difficult becoming or staying pregnant.

Compared to women, men are stronger and perform better in sports

Biological sex is a primary determinant of athletic performance because of fundamental sex differences in anatomy and physiology dictated by sex chromosomes and sex hormones.
Adult males are stronger, more powerful, and faster than females of similar age and training status.
Males typically outperform females by 10%–30% depending on the requirements of the event.
Before puberty, sex differences in athletic performance are minimal. Significant differences emerge at puberty (-12 years) due to anabolic effects of testosterone in males. Testosterone levels rise 20-30-fold in males during puberty and are 15 times higher in males than females by age 18.
Compared to women, men have increased skeletal muscle mass due to larger muscle fiber cross-sectional area, especially fast, type II fibers; lower percentage body fat; higher hemoglobin concentration and mass; larger ventricular mass (heart) and cardiac volumes; larger airways and lungs; greater body height; and longer limbs.

Reference - American College of Sports Medicine, 2023

Reference - Hilton & Lundberg, 2021

Reference - Hunter et al, 2023

Reference - McArdle et al, 2023

Reference - Thibault et al, 2010

* = statistically significant
The "brain sex classifier" of men who self-identify as transgender are more similar to the brains of men than to the brains of women. In fact, the brains of men who think they are women appear to have a "malformed" version of the brains of healthy men.
Note: This 2022 study was performed by transgender-activists who falsely stated the brains of men who self-identify as transgender are more similar to the brains of women than to the brains of men. Clearly, the graph of the results shows this is not the case and the authors are simply biased.