Biogenesis is the scientific principle that living organisms arise from pre-existing life. This concept opposes the idea of spontaneous generation, which suggested that life could emerge from non-living matter. Biogenesis emphasizes that all life forms, from the simplest bacteria to complex animals, originate from other living entities through processes like reproduction. The theory of biogenesis was significantly supported by the experiments of Louis Pasteur in the 19th century. He demonstrated that microorganisms in the air could contaminate sterile solutions, leading to the conclusion that life comes from existing life. This foundational principle is crucial in fields like biology and medicine.