In his book, Darwin never referred to the origin of life. The primitive understanding of science in his time rested on the assumption that living beings had a very simple structure. Since medieval times, spontaneous generation, the theory asserting that non-living materials came together to form living organisms, had been widely accepted. It was commonly believed that insects came into being from food leftovers, and mice from wheat. Interesting experiments were conducted to prove this theory. Some wheat was placed on a dirty piece of cloth, and it was believed that mice would originate from it after a while.
Similarly, worms developing in meat was assumed to be evidence of spontaneous generation. However, only some time later was it understood that worms did not appear on meat spontaneously, but were carried there by flies in the form of larvae, invisible to the naked eye.
Even in the period when Darwin wrote The Origin of Species, the belief that bacteria could come into existence from non-living matter was widely accepted in the world of science.
However, five years after Darwin’s book was published, the discovery of Louis Pasteur disproved this belief, which constituted the groundwork of evolution. Pasteur summarized the conclusion he reached after time-consuming studies and experiments: "The claim that inanimate matter can originate life is buried in history for good."10
Advocates of the theory of evolution resisted the findings of Pasteur for a long time. However, as the development of science unraveled the complex structure of the cell of a living being, the idea that life could come into being coincidentally faced an even greater impasse.