A kilocalorie is the amount of heat required to raise the temperature of 1 kilogram of water one degree Celsius. The "calorie" we refer to in food is actually kilocalorie. One (1) kilocalorie is the same as one (1) Calorie (upper case C). Hunting and gathering cultures used 100,000 kilocalaries per day. Neolithic farming villages needed 10 times that number. Contemporary industrial states consume over 50 trillion per day. (Harris, Cultural Materialism.) The energy surplus we had in the Neolithic era went to supporting an increased population, rather than a better quality of life.