What is the Origin of Life? Part-3 (Theory of spontaneous generation/Theory of abiogenesis)

Theory of spontaneous generation/Theory of abiogenesis:

According to this theory, living organisms could arise/originate suddenly and spontaneously from any kind of non-living matter. It is also called abiogenesis/autobiogenesis or biopoesis. Egyptians believed that mud of the Nile river could spontaneously give rise to many forms of life.

Some statements on sopontaneous generation are as follows:

i) Thales (624-548 BC) suggested that oceanic water was the mother from which all living forms originated.

ii) According to Empedocles, life originated by itself from non living matter and imperfect forms were replaced by perfect forms.

iii) Aristotle (384-322 BC): The Greek philosopher Aristotle (384-322 BC) was one of the firm believers in spontaneous generation of life. Aristotle proposed that living forms are animated forms of non-living matter. He thaught that animals might originate spontaneously from the soil, plants, or other unlike animals. He further stated that the vital forces operate constantly and improve the living world. He saw beings as arising in one of three ways, from sexual reproduction, asexual reproduction or nonliving matter. In addition Aristotle opined that dead leaves falling from a tree into a pond would transform into fishes and those falling on soil would transform into worms and insects. Some insects develop from morning dew and rotting manure. It is observable that aphids arise from the dew on plants, fleas from putrid matter, and mice from dirty hay. This belief remained unchallenged for more than two thousand years.

iv) Virgil (70-19 B.C.): 300 years later at about 40 B.C. Virgil (70-19 B.C.) gave directions for the artificial propagation of bees.

v) Jan Baptista van Helmont (1580-1644): van Helmont concluded in late 1500’s that mice could be created from a dirty shirt. He placed grains of wheat and a sweated dirty shirt in a container and 21days later mice was appeared. He deduced that sweat caused wheat to ferment into mice. Through this experiment he supported spontaneous generation or abiogenesis. 

 vi) Francesco Redi (1621-1697): In the 17th century (1668), the Italian physician Francesco Redi attacks the spontaneous generation theory and disproves it for large organisms. For the first time he proposed through experiments that life could arise only from pre-existing living things.

Experiment by Redi: He sealed meat inside four closed flask, while leaving another four meat filled flasks open. Soon the meat in the open flasks was full of maggots. Flies were entering and leaving the flask. Even after many days no worm appeared in the closed and sealed flask. This experiment confirmed his idea that new life can come only from early life.

vii) John Needham (1713-1781): John Needham believed that spontaneous generation could occur in the case of micro-organisms. In 1745 Needham adds chick broth to a flask and boils it until it was sterile, lets it cool under open air and then seal it. Several days later, microbes grow in broth and he proposes it as an example of spontaneous generation.

viii) Lazzaro Spallanzani (1729-1799): Spallanzani believed that Needham allowed contamination in by exposing the broth to air while it was cooling. 25 years later in 1768 Spallanzani repeated the experiment of Needham, but remove all air from the flask (Boiled the broth. Before it cooled, he sealed the flask. When it cooled, it formed a vacuum inside). No growth occurs/appeared. However, critics said that he apparently "killed the life force" by not allowing it to come in contact with air. 

What is the Origin Of Life? Part-4 (Theory of Biogenesis or disprove/refute of spontaneous generation) 

What is Origin of Life, part-2 (Introduction and Historical Development) 

 What is Origin of Life, part-1 (Introduction and Historical Development)