Aristotle gave spontaneous generation a systematic place in his biology, well beyond a vague ancient intuition. In History of Animals he described some insects, shellfish, eels, and fish as arising from mud, sand, decaying matter, or other material without parents. In one striking passage he argued that certain fish “come spontaneously into existence” rather than from eggs or copulation.
That made spontaneous generation part of a broader explanatory system: organisms could reproduce normally, but some forms of life were thought to originate directly from suitable matter. Aristotle’s biological and natural-philosophical works later became enormously influential. After translations of his corpus circulated in medieval Europe, Aristotelian natural philosophy became central to university teaching, helping keep ancient questions and frameworks active subjects of scholarship rather than museum pieces.
The doctrine was repeatedly narrowed before it finally collapsed. Francesco Redi challenged spontaneous generation of larger animals in the 17th century; Needham and Spallanzani debated microorganisms in the 18th. In the 19th century Félix Pouchet still defended spontaneous generation while Louis Pasteur opposed it. Pasteur’s swan-neck-flask experiments helped show that sterilized broth remained sterile when airborne contamination was excluded.
This history concerns the repeated appearance of organisms under ordinary present-day conditions. It does not answer the separate origin-of-life question of how the first self-replicating systems arose on the early Earth.