Mans greed.
People are naturally greedy, especially when they get on to a good thing. They just want more of it, and more and more. If we go down the road that conservationism and environmental science is following, we do see the greed of man. The destruction of the rain forests for luxury woods and development for mass farming.
Many of these problems first start with out demands for quality goods and cheap food, developing nations are trying their best to get out of poverty and improve their lot. Luke 12:15, 1 Thessalonians 2:5.
Ask me and I will tell you! 
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