By the way - have you heard about the theory that the Amazon Rainforest used to be a man-shaped "park", "orchard" or "garden" ??? Check:
http://news.mongabay.com/2005/1017-amazon.html
It is originally in this book:
http://www.amazon.com/exec/obidos/ASIN/140004006X/mongabay-20
According to Charles Mann
terra preta - very fertile soil of the Amazon - is largely the result of human activity.
According to this theory in the past the Amazon was a patchwork - even better, a checkerboard - of many small plots of agricultural land intermingled with similar small plots of forest deliberately spared by humans for wildlife. Essentially - it was a rain-park or a huge garden inhabited by both humans and animals, not a wild rain-forest. Local humans developed a system which could sustain (feed) large population without destroying ecological balance and wildlife! Eurasian diseases killed up to 95% of the population as the result of which human activity in the Amazon vastly decreased and plots of agricultural land were quickly taken over by forest and wildlife.
But the specific soil - terra preta - gives evidence that in the past the area was much more densely populated than today. E.g. this soil contains crushed "grains" and larger pieces of man-made pottery (and not just in particular spots, but over the whole region!). Moreover, it is assumed that certain wild plants which today grow in the Amazon were originally domesticated, and perhaps bred through selection from local wild plants, or introduced from outside to this region, by humans.
After local humans got largely extinct, these domesticated plants continued to grow but they went back to the wild.
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Some of remnants of Amazonian tribes - e.g. the Matsigenka Paquirianos of Peru - still use a very similar system as that from Charles Mann's theory.
We can call it a "glade-plot-orchard" system of agriculture inside a forest. Knowledge about medical properties of various plants & herbs is also huge.
I would say that those Amazonian forest tribes had better medicine than Europeans of the time. Largely because drugs were growing around them.
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Check also:
http://yurileveratto.com/en/articolo.php?Id=209
To summ up - many things indicate that the population density of the Amazon 600 years ago was much, much higher than TODAY, in 2014.
Maybe we could learn something from those people - how to re-populate this region without destroying its nature and wildlife ???
Our civilization is not used to live just next to nature. We create nature reserves but they are far away from our homes, not in our backyards!