The term is also used for the assertion that living matter can only be generated by other living matter, in contrast to the hypotheses of abiogenesis which hold that life can arise from non-life under suitable circumstances, although these circumstances still remain unknown.
Until the 19th century, it was commonly believed that life frequently arose from non-life under certain circumstances, a process known as spontaneous generation. This belief was due to the common observation that maggots or mold appeared to arise spontaneously when organic matter was left exposed. It was later discovered that under all these circumstances commonly observed, life only arises from the replication of other living organisms.
A second meaning of biogenesis was given by the French Jesuit priest, scientist and philosopher Pierre Teilhard de Chardin to mean the origin of life itself due to an inherent drive of matter towards higher consciousness, an extension of the now disproven orthogenesis hypothesis.
Pasteur's (and others) empirical results were summarized in the phrase, Omne vivum ex vivo (or Omne vivum ex ovo), Latin for "all life [is] from [an] egg". This is sometimes called "law of biogenesis" and shows that modern organisms do not spontaneously arise in nature from non-life.
No cellular life has ever been observed to arise from non-living matter. The construction of viable viruses capable of infection and evolution from abiotic material has been reported; however, considerable debate still exists regarding if viruses are actually alive. Various other experiments into the possibility and potential mechanisms of abiogenesis have also been reported but remain unproven.