"What ones did you pick?"

"I argued that a cleaning procedure had to remove all traces of disease-carrying microbes and other microscopic traces associated with contact with an original pollutant, which also meant it has to be thorough enough to remove dirt and other substances, and I propose some substances which have qualities which make them good for testing this. I argued that it could not involve reconstituting something which is pollution by its nature - for example, if you teleported the contents of a sewer, they'd still be polluted, even if you used newly clean atoms to make them up - but that it wasn't obvious that should apply to reds, because someone made of clean atoms in the patterns of a red wouldn't be red really, and then I discussed why I thought that."

"They wouldn't be red? What would they be?"

"I don't know! That argument generated a lot of debate, and many people feel they would be red."

"Can there be people who don't have a caste at all?"

"Well, there could be aliens."

...giggle.

Wink. 

"Castes weren't new though."

"That makes sense. I would expect most societies to have them; they solve a lot of problems which would otherwise be very hard to solve."

"...I don't remember if the exact ones were new."

"You wouldn't need them to contain the same categories at all to get the benefits, you would just need a way to make sure that your next generation isn't entirely powerful rich people."

"Is that what castes are for?"

"Not what they're for - they're for specialization - but whether you need that depends a lot on what kinds of jobs your world has and how your species learns and what species traits are hereditary, it's not at all obvious to me you'd get castes just from that without the additional pressure of population."

"Can you say that differently?"

"Castes are for specialization. Whether castes are a good way to do that depends on lots of things about a species - how much they inherit traits from their parents, how much they need different traits to do work, how they learn, how long they live."

"Why those things?"

"Well, if all of the jobs required good judgment and prudence and intelligence, then we would only need blues, right? Castes only make sense if we need some strong people and some creative people and some meticulous people, and not all species might be such that those are separate things, or such that different jobs require different ones. If those traits existed and were all needed but were not heritable, then castes would make no sense. If they could not learn at all, then maybe you'd need way more castes so everyone was born with an aptitude for their job. If people lived very long lives, castes would be less appealing because it would be very hard to shift the labor force to reflect new needs."

"How would you make it so all the jobs only needed one kind of thing?"

"I don't know. Maybe aliens uploaded themselves and now all they need are programmers to invent new virtual things to interact with and artists to create new media to consume."

"What's uploaded?"

"Another thing that doesn't exist yet. We might someday be able to run peoples' brains on computers. Brains run on math so it might be possible in principle."

"Brains run on math?"

"The universe runs on math. - with the possible exception of your animal product sensing. Everything about the universe except that runs on math."

"...what do you mean runs on math and why can't my food thing?"