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Slightly off topic, but do you have any thoughts as to why the warmer regions of the world (Africa, South Asia, South America, etc.) did not develop agriculture before the Holocene? Presumably the cold of the ice age would have had less effect there.

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Mar 11, 2023·edited Mar 11, 2023Author

Thanks for the question. I'll preface this by saying that I'm no expert, and that there may already be existing theories out there which I haven't heard.

My understanding is that tropical soils are inherently poorly suited for agriculture. They are thinner and have less organic material, which makes it more difficult to grow crops in tropical regions even today. High rainfall leaches nutrients from the soil.

In more northern climates, the cycle of the seasons causes leaves to fall which become a natural mulch and fertilizer during the winter. This makes soils richer and more suitable for growing crops. My understanding is that soils in Fertile Crescent were very suitable for agriculture before they were destroyed by civilization. I think Diamond covers much of this.

Add to that the fact that seasonality in northern climates means that there is a growing season and fallow season. This means that food surpluses have to be stored up during the growing season, which provides an inventive for more intensive cultivation of food resources. In the tropics, some wild food source is pretty much available throughout the year, so there is less of an incentive to grow crops (i.e. "why work when there are so many mongongo nuts in the world?")

The evidence is that people don't start growing their food unless they have to. It's worth noting that we don't know for sure the extent of cultivation thousands of years ago, and it may have been more extensive then we normally think. Colin Tudge notes that some peoples like the Mbuti will take up growing crops and animal husbandry during lean times and abandon it once things improve. So there could have been agricultural-like activities in those regions that we just don't know about. There is evidence of people using fire to shape environments as far back as 70,000 years ago. But it never crossed the line because food was still plentiful relative to population size. Small population sizes played a role too--agriculture is usually associated with population growth.

Migration could have also been a viable strategy in tropical regions--IIRC, people some think that the migration beyond Africa could have been prompted by climate change. It's notable that agriculture really took off once that was no longer a viable option because everywhere was already filled up, so intensification was the only option left.

Anyway, those are just some initial thoughts.

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