In his book, Darwin never referred to the origin of life. That is because 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, which asserts that non-living materials came together to form living organisms, had been widely accepted. In that period, 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, maggots developing in rotting meat were assumed to be evidence of life originating from inanimate materials. However, it was later 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. At the time 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 the publication of Darwin’s book, Louis Pasteur announced his results, after long studies and experiments, which disproved spontaneous generation, a cornerstone of Darwin’s theory. In his triumphal lecture at the Sorbonne in 1864, Pasteur said: “Never will the doctrine of spontaneous generation recover from the mortal blow struck by this simple experiment.“ (Sidney Fox, Klaus Dose, Molecular Evolution and The Origin of Life, W. H. Freeman and Company, San Francisco, 1972, p. 4.)
For a long time, advocates of the theory of evolution resisted Pasteur’s findings. 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.