Food prices have swelled many times in history, but Goldman Sachs wasn't to blame for those bubbles and I doubt they're at fault for these. See a short list of previous food riots which catalysed political upheavals here: http://en.wikipedia.org/wiki/Food_riot
Derivatives are actually incredibly useful tools in agriculture because they allow a farmer to embark on the long-term commitment of growing crops with the peace of mind that (s)he'll have guaranteed customers for the final product. This is why the MGEX has been running since 1883: http://en.wikipedia.org/wiki/Minneapolis_Grain_Exchange
Derivatives are actually incredibly useful tools in agriculture because they allow a farmer to embark on the long-term commitment of growing crops with the peace of mind that (s)he'll have guaranteed customers for the final product. This is why the MGEX has been running since 1883: http://en.wikipedia.org/wiki/Minneapolis_Grain_Exchange