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Male humans produce sperm and much higher levels of testosterone than females. Females produce ova and offspring if their eggs are fertilized and implanted. Individuals who are sterile still have either male or female anatomy which serves sexual functions for the individual. Virtually everyone on earth qualifies as one sex or the other, with or without malfunctioning or variations. Is this binary a social construct?
Does the collective agreement of society give male and female organs their functionality? Absolutely not. Humans did not always have an understanding of how pregnancy happened, and yet it happened anyway. Individuals who don’t know about or understand reproduction can and do get pregnant via sex. No matter how many people got together and decided that females inseminate males there would be no change in the function of testes or ovaries.
The functionality of human reproductive organs is also impervious to cultural or geographical differences. All over the world people get pregnant and have babies by mixing sperm from males with ova from females. There is no exception.
Removing humans from the equation also has no effect on the biological reality of mammalian reproduction. Male mammals are male, female mammals are female, and only one of the two can give birth.
Biological sex is not and never has been a social construct.
Another example is gender. Femininity is the easiest example to discuss.