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Thread: Hindcasting global population densities reveals forces enabling the origin of farming

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    Hindcasting global population densities reveals forces enabling the origin of farming

    The invention of agriculture changed humans and the environment forever, and over several thousand years, the practice originated independently in a least a dozen different places. But why did agriculture begin in those places, at those particular times in human history?

    Using a new methodological approach, researchers at Colorado State University and Washington University in St. Louis have uncovered evidence that underscores one long-debated theory: that agriculture arose out of moments of surplus, when environmental conditions were improving, and populations lived in greater densities.

    The first-of-its-kind study, "Hindcasting global population densities reveals forces enabling the origin of agriculture," published in Nature Human Behaviour, lends support to existing ideas about the origins of human agriculture. In contrast, they found little support for two other, longstanding theories: One, that during desperate times, when environmental conditions worsened and populations lived at lower densities, agriculture was born out of necessity, as people needed a new way of getting food. And two, that no general pattern exists, but instead the story of agriculture's origins is tied to unique social and environmental conditions in each place.

    Senior author Michael Gavin, an associate professor in CSU's Department of Human Dimensions of Natural Resources, said the findings and the general methodological approach may help explain other watershed events in human history.

    "There have been several key threshold events in our history that changed the entire course of our species," Gavin said. "Agriculture is a link to so many other components for what the world is like today for billions of people. This begins to help us explain a key moment in human history."

    Predicting into the past

    Studying the depths of human history is challenging, as little data are available when looking back tens of thousands of years. Scientists typically rely on archeological evidence, but getting a broad picture is difficult, since archeological digs cover relatively small areas.

    To overcome these limitations, the researchers modeled correlations between the environment, cultural traits and population densities of relatively recent foraging societies, which used hunting, fishing and gathering to obtain food.

    Among the factors they considered as possible predictors of population density: environmental productivity; environmental stability; the average distance travelled when people in a community moved to a new location; whether people owned land or other resources; and distance to the nearest coast.

    This model, the team found, did a remarkably good job at predicting recent population densities, which led the researchers to pair the model with data on past climate. In doing so, they could hindcast, or predict into the past, the potential population density of the entire globe dating back thousands of years.

    Population maps

    This study was the first to produce maps of potential population densities dating back as far as 21,000 years. The researchers used these maps to examine conditions that existed in each of the 12 centers of origin, at the point in time agricultural practices began.

    Patrick Kavanagh, a CSU postdoctoral scientist and one of the study's lead authors, said the different centers of origin for agriculture all showed improving environmental conditions and increasing population densities.

    "All regions that developed agriculture showed the same pattern," he said.

    Researchers believe that improving environmental conditions may have allowed people the luxury of tinkering with new ideas, and that having more people living in one place would allow ideas to be shared and honed, with sparks of innovation following.

    While the researchers found commonalities in the surplus aspect of what was occurring in different locations, that doesn't mean the exact same conditions existed in each center of origin. Socially, the places and people studied were probably very different. In addition, the timing of when agriculture began in these major centers varied over thousands of years, and the species of plants they were working with was different.

    But, amazingly, although the centers of origin varied in time by thousands of years and ranged from the New Guinea Highlands to Central America and the Middle East, they all had one thing in common: improving environmental conditions, and the potential for higher population densities.

    "In all of these major origin centers of agriculture, there were some critical environmental changes that needed to occur," Kavanagh added. "Environmental conditions needed to improve—which we saw in all 12 centers of origin—despite variation in the timing and the diverse geographic locations in which they occurred."

    The research team is now exploring other applications for the maps they produced.

    "It is amazing to examine these maps of the potential population density of the world dating back tens of thousands of years," said Gavin. "We could potentially create them going back to the dawn of our species. This provides a new tool to explore many unanswered questions about human history."

    Read more at: https://phys.org/news/2018-06-agricu...clues.html#jCp


    Hindcasting global population densities reveals forces enabling the origin of agriculture

    The development and spread of agriculture changed fundamental characteristics of human societies1,2,3. However, the degree to which environmental and social conditions enabled the origins of agriculture remains contested4,5,6. We test three hypothesized links between the environment, population density and the origins of plant and animal domestication, a prerequisite for agriculture: (1) domestication arose as environmental conditions improved and population densities increased7 (surplus hypothesis); (2) populations needed domestication to overcome deteriorating environmental conditions (necessity hypothesis)8,9; (3) factors promoting domestication were distinct in each location10 (regional uniqueness hypothesis). We overcome previous data limitations with a statistical model, in which environmental, geographic and cultural variables capture 77% of the variation in population density among 220 foraging societies worldwide. We use this model to hindcast potential population densities across the globe from 21,000 to 4,000 years before present. Despite the timing of domestication varying by thousands of years, we show that improving environmental conditions favoured higher local population densities during periods when domestication arose in every known agricultural origin centre. Our results uncover a common, global factor that facilitated one of humanity’s most significant innovations and demonstrate that modelling ancestral demographic changes can illuminate major events deep in human history.

    https://www.nature.com/articles/s41562-018-0358-8

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    It's behind a paywall, but you can see the figures. Here's a figure showing the potential population density for foragers:


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    it's a nice game, adjusting a model till it fits to explain the present and then extrapolate it to the past

    nice maps though, what are the dates?
    it also would be interesting to zoom in on Europe at the time the incoming farmers were interacting with local HG

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    Another mystery of prehistory almost solved, it seems. Once again innovation arose in places with high population densities. That's typically the case throughout history - at least in Europe and the Middle East, because that pattern doesn't work for India and only moderately for East Asia.
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    Researchers believe that improving environmental conditions may have allowed people the luxury of tinkering with new ideas, and that having more people living in one place would allow ideas to be shared and honed, with sparks of innovation following.
    Very interesting study! About the reasons for this correlation between environmental conditions and the subsequent appearance of agriculture, I for one think they should investigate if part of that had also to do with the increasingly sedentary lifestyle and decreasing needs of going from one place to another far away because of the low density of resources to sustain the population. Natufians for example were, famously, sedentary villagers even before they became farmers, and there are also other much more recent examples of hunter-gatherer societies who achieved a relatively complex sedentary way of life before or even without later developing agriculture or animal husbandry, because they were blessed with a particularly productive environment around them, as was the case of the Northwest Pacific tribes of the USA before whites came in.

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    Quote Originally Posted by bicicleur View Post
    it's a nice game, adjusting a model till it fits to explain the present and then extrapolate it to the past

    nice maps though, what are the dates?
    it also would be interesting to zoom in on Europe at the time the incoming farmers were interacting with local HG


    I found a description of the supplements here. It seems to go back 21,000-4,000 years:

    https://static-content.springer.com/...MOESM1_ESM.pdf

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    2 members found this post helpful.
    Yes, this dovetails nicely with the work done on Natufians, as Ygorcs brought up. Quite some time ago I had posted this video which talks about how much abundance there was in terms of natural resources in their areas, and how this led to population growth even before the development of agriculture.




    Another aspect of this is that the larger the population, the more mutations there are, and the more selection there is genetically for beneficial mutations.
    It all works hand in hand.
    Last edited by Angela; 05-06-18 at 20:10.


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    Quote Originally Posted by Jovialis View Post
    I found a description of the supplements here. It seems to go back 21,000-4,000 years:

    https://static-content.springer.com/...MOESM1_ESM.pdf
    thanx

    Interesting to see the westcoast of Iberia is red.
    It is because of high tides and estuaries rich in plankton meeting the Atlantic Ocean.
    I think it was an important area where local HG adopted agriculture, it is how EEF got admixed with WHG.
    The earliest megaliths were in Evora, Portugal 8 ka, that was before arrival of farmers over there.
    The incoming EEF didn't consume fish, but for the local HG it was their main foodsource.
    The megalithic neolithic may have spread from there. The megalithic sites contained more Y-DNA I than other neolithic sites.

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