Why is our body temperature 98.6 F (37C)?

       This is like asking-why there is life? I can not answer "why" but I can tell you that in many organisms (BUT NOT ALL), 98.6 F (37 C) is the temperature at which most reactions occur most efficiently. Our body enzymes have adapted to that temperature. When a mammal hibernates, its body temperature actually falls and they are much less active. Not only do they appear to be asleep, but they breathe less often and their heart rate is greatly reduced. Some organisms have adapted to other temperatures, mostly the temperature of their surroundings. When their body enzymes are isolated and studied in the lab, they are found to function most efficiently at the higher (for "thermophiles") or lower (for "psychrophiles") temperatures where their cells normally live in.