Francesco Redi experimentally proved
The theory of biogenesis states that complex living things come only from other living things, by reproduction. Life does not arise from non-living material. In 1668, Francesco Redi disproved the spontaneous generation theory and proved biogenesis. He set up a simple experiment in which he used two jars, both containing dead fish and meat, but with a difference - one was kept closed completely and the other, open. After a couple of days, he observed something really interesting: maggots were formed only on the meat in the open jar as the flies had got the chance to lay eggs on the meat. The closed jar, on the other hand, did not have any worms. This meant that worms could not have been formed spontaneously; they rather were formed only where there was pre-existing life.