Robin Hanson's guess: "our distant ancestors got into the habit of complaining about inequality of transferable assets with a tribe, as a way to coordinate a veiled threat to take those assets if they were not offered freely." I'm not sure agree with this 100%. over access to salt, as mentioned in is just a signal for me to take stuff from others, in the same way hunger is a signal for me to eat stuff.(Yes, many of us modern humans are generally pretty good about suppressing this "things are unfair" instinct, but that doesn't mean our ancestors were.) To replicate one's genes, it's useful to have certain things like food, water, and respect.For some/all of these characteristics, there's a bell curve--many people in the middle and fewer people at the extremes. One of the things that comes up a lot on this blog is how irrational people tend to get when talking about politics.For a really rousing political argument, you need group identification--hence the Greens and the Blues in Eliezer's original politics essay.
we've got plenty of food and competing with outsiders is useless!
"Seek first to understand, then to be understood." (Note: This can be tough.) To give a concrete example: Maybe women have a preference for not being objectified sexually that men don't share.
Men can respect and work to achieve that preference even if they don't share it--empathy over fairness!
Robin Hanson has wondered why folks seem concerned about inequality based on some stuff, like race, gender, sexuality, ethnicity, and disability, but not other stuff, like height, appearance, intelligence, sleep, conscientiousness, and perhaps most importantly, happiness.
My explanation: Race, gender, sexuality, ethnicity, and disability are fairly discrete ways of classifying people.