Found 2 comments on HN
whack · 2017-02-17 · Original thread
I actually don't recall where I read that. It was one of the following 2 books:

https://www.amazon.com/Sapiens-Humankind-Yuval-Noah-Harari/d...

https://www.amazon.com/Tribe-Homecoming-Belonging-Sebastian-...

I wouldn't be surprised if the book derived that number from the link you gave either.

clumsysmurf · 2016-12-29 · Original thread
A recent book that explores the loss of community when combat veterans come home, and how this may contribute to PTSD:

"Tribe: On Homecoming and Belonging"

https://www.amazon.com/Tribe-Homecoming-Belonging-Sebastian-...

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