When people settled down, either because of concentrated local food resources or agriculture, this changed. Societies became stratified and unequal. Nobles, princes and social classes rapidly become entrenched. The transformation seems to have been triggered by the invention of property. In a mobile HG band, property is what you can carry, and nobody has enough to be jealous of, or if you are jealous of it, you probably won't be able to carry it. Settlement changes that.
Various forces combined to erode and destroy much of this system over the last several hundred years, but the class system is a hardy weed that continues to sprout.
Today wealth is essentially the only element of social class that survives, but it has become tremendously important. Every year Oxfam compiles the number of the richest of the rich who together have more wealth than the bottom half of the human race. This year than number was 26. It's unlikely that this was ever true before in previous history.
The old, indeed ancient, idea of levelling by taxation has become popular again. Of course it's not popular with the ultra-rich. Dutch historian Rutger Bregman created a scandal at Davos this year when he dissed the billionaire attendees for dodging taxes.
“I hear people talking the language of participation, justice, equality and transparency but almost no one raises the real issue of tax avoidance, right? And of the rich just not paying their fair share,” Bregman tells the Time magazine panel on inequality.