Suppose men and women are equally praiseworthy in every way. Both genders are equally honest, fair, peaceful, hard-working, fun-loving, and so on. With one key exception, both genders share the same trait preferences: The average man places as much weight on honesty, fairness, and so on as the average woman. The key exception: everyone’s heterosexual.
Suppose further that no one’s evaluations are gender-biased. Men have no tendency to see women as worse than they really are, and women have no tendency to see men as worse than than really are. People do however tend to get to know more people of the same sex because, say, men hunt together and women gather together.
Claim: Even in this rarefied setting, sexism will endogenously arise. Men will find the men they personally know to be better than the women they personally know. Women will find the women they personally know to be better than the men they personally know. And if people extrapolate from the people they personally know to all humanity, men will think that men are better than women, and women will think that women are better than men.
Hint: Compare the selection filter you apply to potential friends to the selection filter to apply to the romantic partners of your friends.
Please show your work.