A recurring number:
About twenty five years ago I was chatting with my mother, then alive, and trying to explain what I was already toying with, which was the idea that the fertility of a village is ample while that of a city is inadequate.  She wasn’t buying it but listened carefully.  Then I said I thought typical village size was about a hundred people.  She said very quietly, “Two hundred.”  Her tone was almost like, “I shouldn’t be saying this.”  Had I the presence of mind I would have asked her where she got that number.  But I have remembered it ever since.  That’s not saying much.  My memory is terrible.

More recently I have worked on computer simulations of the fertility of large and small populations.  I found that in my model a population of two hundred generally worked well.  But I was laboring against the limitations of my computer.  In fact I sit here surrounded by the corpses of computers I have burned out over the years.  I still need more power, lots more.  So in an effort to reduce the computational load I frequently used a population of 100. After all I was only trying to demonstrate a model, not reality, which is far from the computer power I wield.  But 200 really worked best.  Then I found an old map that indicated that traditional agricultural communities, although their villages were smaller than a hundred homes, apparently lived in social groups more like two hundred.  I also found evidence that Isaac Newton, about the time the map I saw was published, had evidence for the same number.  200 or 100 families.  Children and elders do not figure into the calculation. 

It’s not that he said as much.  He laid out his evidence but did not interpret it for us.  He must have been a most difficult man to deal with, but my respect for his raw brain power only continues to grow.

So recently I was reviewing the work of J. Calhoun, the guy who raised a lot of mice, giving them all the food, space, water and nesting material they could use and watched their numbers increase and then collapse to extinction.  Without commenting on it, he put a note on the graph of their doomed history:  N = 150 Optimal No. of Adults.  But how did he know that?  What was he thinking caused it?  I have no idea.

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