Similar thoughts came up in the thread about intra-tribal delineations. And using the Dunbar number, or other “thresholds”, to determine the development of the tribe, is also discussed under the long thread about economy.
I agree with you both, @Sargon and @louis.mervoyer, in that using just a number is too simple a mechanic. And sociology and psychology is sufficiently complicated for a single number to be completely off in most cases. I varies depending on hundred of variables, from person to person, with some people being able to have stable and worthwhile relations with hundreds of people, and others… only a few. It is science, but too much might be read into it.
In this case what we’re dealing with is both carrying capacity from a biological perspective (as in “how many people can feed themselves in this area”), but also in a societal sense (“how many people can stand each other / maintain a working society”).
There always is a limit to the first one, a Malthusian limit, but that does change once agriculture comes into play, as @sargon says. I’m not sure we’ll discover it as rapidly as within ten minutes, but that’s besides the point There should however be a possibility for the leader of the tribe, the player, to deal with a possible Malthusian disaster, overpopulation, by sending people away. An expedition as it were, similar in some ways to the famous colonies of ancient Greece, Phoenicia, Carthage and Rome. I believe this would fit the clans @demon mentioned.
When it comes to the societal limit, that’s a lot trickier. Both politically and economically though, there is a very great difference between fifty people working together to survive, and a thousand people of a well-established town, whose inhabitants may rarely meet, and prioritise completely different things in life. A free market and competition surely won’t exist in the first case, when all the members are very closely related, fighting to stay alive, and there is no specialisation. At some point though, your tribe will switch from one big “family”, to several “families”, and with this will start serving themselves, prioritising themselves, trading and bartering, specialising, relying less on communal labour than just… a primitive market. With this change, everything else changes, be it culture, politics, technology. Civilisation in it’s truest sense is born.
This of course won’t happen over night. I don’t really know how it would be implemented, but surely gradually, piece by piece, day by day, event by event. If certain changes are not made though, certain adaptations, the tribe will surely not be able to remain united, a single society surviving together through all its parts.