Our understanding of diseases have dramatically changed over human history. Early civilisations believed health and disease were directly caused by the gods. This is why priests and priestesses were also healers and doctors.The ancient Greeks introduced the four humours theory, namely that the body was composed of four fluids: blood, phlegm, yellow bile, and black bile. Disease and illness were caused by imbalances. Treatment was to rebalance these fluids.Our modern underst...