1. SPONTANEOUS GENERATION (ABIOGENESIS) OR
BIOGENESIS
⦿ Men of ancient times (Thales, 624-548 B.C.;
Anaximender, 611-547 B.C.; Anaximenes, 588-524 B.C.;
Empedocles, 504-433B.C.; Aristotle, 384-322 B.C.;
Epicurus, 341-270 B.C.; and Socretius 99-55 B.C.).
⦿ They believed that all living organisms could spring forth
spontaneously from non-living matter.
⦿ This belief has been referred to as Doctrine of
Spontaneous Generation or Abiogenesis (a= not; bios=
life; genesis= origin)
⦿ They believed that frog, snakes and mice could be born
of moist soil, that could emerge from manure, and that
maggots could arise from decaying materials.
2. ⦿ Van Helmont (1577-1644) devised a method for
manufacturing mice. He recommended putting some
wheat grains with soiled linen and cheese into an
appropriate receptacle and leaving it undisturbed for
some time.
⦿ Mice would then appear. However, the idea of
spontaneous generation continued until the mid 19th
century with great oppositions against it.
3. Controversy over Spontaneous Generation
⦿ Actually, it was the discovery of microorganisms and
improvements in microscopy that enabled scientists to think
seriously about the origin of life.
⦿ Francesco Redi (1626-1679), an Italian physician,
demonstrated during 17th century by simple experiment that
spontaneous generation (abiogenesis) does not exist.
⦿ He took rotting meat pieces and placed then in jars and
sealed some of these jars tightly and left other open.
4. ⦿ In a few days, maggots appeared in open jars in which
the flies went freely in and out and laid their eggs on
meat.
⦿ Contrary to it, the sealed jars in which the flies could not
enter did not show any maggots.
⦿ From these observation Redi concluded that the
maggots arise from eggs laid down by parent flies and
that the maggots can not appear spontaneously.
5. LOUIS JABLOT
In 1670 Jablot conducted an experiment in
which he divided a hay infusion that had
been boiled into two containers: a heated
container that was closed to the air and a
heated container that was freely open to
the air. Only the open vessel developed
microorganisms. This further helped to
disprove abiogenesis.
7. ⦿ Still, the supporters of abiogenesis did not agree with Redi
and argued that the free air, which was considered as “vital
force” necessary for spontaneous origin of life, was not
allowed to reach the meat placed in sealed jars.
⦿ Redi set up new set of experiment in which he covered jars
with fine muslin cloth or gauze instead of sealing them
tightly and thus allowed free air to go in and out of the jars.
⦿ Even after doing so the maggots appeared only in those
jars in which flies were allowed free to go in and lay their
eggs on the meat.
9. ⦿ Even after Redi’s convincing demonstration, abiogenesis
versus biogenesis controversy continued.
⦿ John Needham (1745) advocated that even after he heated
chicken broth and corn infusion (nutrient fluids) before
pouring them into covered flasks, the cooled solution
showed existence of tiny organisms in them and thus he
claimed that the organisms originated spontaneously from
nutrient fluids.
⦿ Later, that this result was due to insufficient heating which
failed to kill heat resistant forms of bacteria containing
endospores but nothing was known about endospores at
that time.
10. ⦿ In the year 1765, twenty years later Lazzaro Spallanzani
demonstrated that nutrient fluids of Needham did not
contain microorganisms when they were subjected to
prolong heating after being sealed in flasks.
⦿ He explained that the microorganisms from air probably
had entered Needham’s solutions after they were boiled.
⦿ Needham responded to it and said that the free air the
“vital force”, present inside Spallanzani’s sealed flasks
had been destroyed by heating and therefore,
microorganisms did not appear in nutrient fluids in
absence of the “vital force”.
11. LOUIS PASTEUR (1822 - 1895)
⦿ Disproved spontaneous
generation of microbes by
preventing “dust particles”
from reaching the sterile
broth
⦿ In 1861 completes
experiments that lays to rest
spontaneous generation.
⦿ Showed microbes caused
fermentation and spoilage
12. PASTEUR’S EXPERIMENT
trapped airborne organisms in cotton; he also
heated the necks of flasks, drawing them out into
long curves, sterilized the media, and left the flasks
open to the air.
In this way Pasteur disproved the theory of
spontaneous generation
13. ⦿Disproved by:
• Schwann, Friedrich Schroder and von
Dusch (1830s) – Air allowed to enter
flask but only after passing through a
heated tube or sterile wool
• John Tyndall (1820-1893) – Omission of
dust 🡪 no growth. Demonstrated heat
resistant forms of bacteria (endospores)
14. ⦿ John Tyndall, an English physicist, in the year 1877.
⦿ He explained that bacteria exist in two forms: Heat labile
forms (thermolabile) which could be killed by exposure to
high temperatures, and heat- resistant forms which could
not be killed by continuous boiling of the broth and after
the broth has cooled, they resulted in microbial growth in
such broths.
⦿ He further stated that if such broths are subjected to
intermittent boiling (discontinuous boiling) on successive
occasions, a process now popular as tyndallization, the
heat- resistant forms of bacteria will be killed and the
broths become completely free of them, and do not show
any microbial growth.
15. ⦿ It so happens because the first boiling kills
vegetative cells of bacteria but endospores
remains as such.
⦿ The endospores now germinated in cooled broth
and produce new bacterial cells which are killed
during further boiling and so on. In this way,
Tyndall validated Pasteur’s results and helped
ending the debate on abiogenesis versus
biogenesis.
