Who mentioned national lines? (1) The original article, which was talking about, e.g., the chances of moving out of the top or bottom 10% by wealth of US society. (2) The person you were replying to (you can tell he was talking about the US by, e.g., comparing his figures for the $250k proposal to the US population, though I think he misunderstood the proposal). (3) The two people who replied to you.

Or, in other words, apparently everyone else in this thread apart from you. How is one supposed to tell that "we have insane mobility compared to any other society at any time in human history" was meant to mean everyone, worldwide?

Indeed, how can that possibly be true (what do you think is the mobility rate out of the poorest 10% of the world population?), or make sense (given that it requires that you regard, say, the US, China, Afghanistan and Burundi as parts of a single "society")?

I stand by my statement. the world, on net, has more income mobility now than at any time in the past. everyday is pretty much the best day the world has ever seen from a net welfare standpoint.

Would you care to present your evidence that the world has more income mobility now than at any time in the past?

(And, FWIW, I am still having grave difficulty believing that you really meant "the world" when you said "we".)

For the whole world you may be right today. That why I put the question mark in my comment. (Lots of people here are from the US and assume everyone is.)

I do agree that measured by income the world has entered a golden age. But I do not know whether mobility in income quantiles is at its peak: You can have a lot of mobility at a very low level of income, too. And in the stone age people were probably more alike in income, so that quantiles were closer together and more easily shuffled just by random changes. (Not that this is a good or bad thing per se.)