The very earliest bakers observed that soft dough left in the air would rise. Unknown to them, yeast from the air "contaminated" the bread, began to grow, and produce carbon dioxide. Carbon Dioxide caused the bread to rise. Later, cooks began to save some of the soft dough (before much flour was added) from the previous loaf to use in the next loaf. This saved portion was called the mother. What is in the mother and why was it important to save it in a cool place?
There seems to be a fine line between symbiosis and parasitism when you examine the relationships between fungi and plants. What hypotheses could explain how different selective pressures might have caused particular fungal species to evolve one or the other relationship? Under what circumstances might a mutualistic relationship evolve between fungi and plants? A parasitic relationship and value?