This part of Harari's book have been debunked quite a few times already: his views of pre-agricultural are romanticized and doesn't match with the work of the specialists of this period. (While Harari is indeed an historian, he's a specialist of medieval times and has little authority on early-humans history).
Btw, I'm not even disagreing with you about agriculture, I just wanted to point out that quoting Harari on that has really little value.
That said, I'm no historian, just a layperson who found Harari's work (so far -- I haven't yet finished "Sapiens") thought-provoking and interesting. In the relevant early chapters his perspective is refreshingly different from the norm -- in some ways comparable (for me) to Zinn's "A People's History of the US", in that it provides a PoV sufficiently removed from the standard narrative to serve as a reminder of how shallow and incomplete any one-sided version of events must be. The GP's citing of Pinker likely belongs in this camp, too: referencing an author whose ideas have merit (eg Pinker's computational theory in "How the Mind Works"), independent of their ultimate status as authoritative works.
You might think this, but the historical pattern -- everywhere -- is that farmers stay where they are and get conquered by more mobile non-farmers. They don't so much fight as submit.
What happened was that farming was so successful that the human population boomed. When famine did occur, it caused more deaths because there were more humans.
Also it’s a bit of a trap: as soon as you switch over you cannot go back, as foraging cannot sustain as many people. You will have to constantly expand to feed the growing population.
>Since they lived in small groups and moved frequently, they had few problems with accumulating waste or contaminated water or food.
>The shift from the hunter-gather mode of living to an agricultural model provided a more secure supply of food and enabled expansion of the population. However, domesticated animals provided not only food and labor; they also carried diseases that could be transmitted to humans. People also began to rely heavily on one or two crops, so their diets were often lacking in protein, minerals, and vitamins
>Rodents and insect vectors were attracted to human settlements, providing a means of spreading disease.
Instead, here's Lifeways of Hunter-Gatherers. From the 2nd ed., p. 200 on disease:
> An important cause of childhood death in many forager societies are infectious and parasitic diseases, including respiratory tuberculosis (TB), influenza, pneumonia, bronchitis, and diarrheal diseases resulting in dehydration.
> Among the Dobe Ju/’hoansi, disease, especially TB and malaria, account for 85 percent of childhood deaths ... and violence for 8 percent.
> Infectious disease (with most deaths occurring among infants and juveniles) accounts for 85–95 percent of Agta deaths
One weakness of current literature is that the mechanism by which adults get sick (contact with other adults) is radically different for living foragers than our paleolithic ancestors. With that said, the fact that we still have these epidemic diseases with us today demonstrates that they were able to survive in ancient populations (excepting plague, which is resident in marmots and only "accidentally" infectious to humans). Perhaps larger regional group sizes and a functioning long-distance forager trade network helped these diseases to survive where they struggle today, but survive they clearly did.
Probably short. Putting aside predation, disease and starvation, there is evidence (see Pinker) that violent death was a common way to go in nomadic tribes.