,➢ Definition: The branch of life science for the study of 'origin of life' and evolution of different
forms of life on earth was called bioevolution or evolutionary biology by Mayer (1970).
➢ The word evolution means to unfold or unroll or to reveal hidden potentialities. Evolution
simply means an orderly change from one condition to another.
➢ Evolution is a slow but continuous process which never stops (irreversible).
ORIGIN OF LIFE
➢ Origin of life is the process by which living organisms developed from inanimate matter
(which is generally thought to have occurred on Earth between 3800 - 4200 millions years
ago).
➢ First life evolved about. 3800-4200 million years back.
➢ There are several theories about the origin of life, like big bang theory, theory of special
creation, theory of eternity, cosmozoic theory etc.
BIG-BANG THEORY
➢ This theory was proposed by Abbe Lemaitre.
➢ According to this theory, the universe originated about 20 billion years ago due to a
thermonuclear explosion of a dense entity. This thermonuclear explosion is called Big-bang.
➢ About 4.6 billion years ago, the origin of the solar system took place by the gaseous clouds
formed due to this explosion.
➢ These gaseous clouds collapsed and converted into flat disc-like structure made up of atoms
and small particles due to their own gravitational pull. This flat-disc like structure is called Solar
Nebula.
➢The very hot central part of this solar nebula became still hotter and converted into the sun.
,➢Now, due to condensation of atoms and dust particles moving around the sun, the formation of
the other planets took place like: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus,
Neptune.
➢ The solid part of our planet earth was called lithosphere and the gaseous part was known as
atmosphere.
➢ When the earth's surface cooled down and its temperature decreased to 100° C, water formed
on it – slowly hydrogen and helium gases formed.
THEORY OF SPECIAL CREATION
➢ The greatest supporter of this theory was father Suarez.
➢ According to the Bible, life and everything was created by God in 6 days from ‘materia
prima’ & man created on 6th day.
➢ According to Hindu mythology, the world was created by God Brahma. According to it, life
has not changed ever since its origin.
➢ Special creation theory lacks scientific evidence so it is not accepted.
THEORY OF CATASTROPHISM
➢ The greatest supporter of this theory was Cuvier.
➢ According to which a gap of certain period, the world undergoes catastrophs (sudden calamity)
to kill almost all the living organisms and new life arises from inorganic matter.
, COSMOZOIC THEORY/PANSPERMIA THEORY
➢ This theory is proposed by Richter and supported by Arrhenius and Helmholtz.
➢ Protoplasm reached earth in the form of spores (pansperms) or other simple particles from
some unknown part of the universe with cosmic dust and they gave rise to various forms of life.
THEORY OF BIOGENESIS
According to this theory, new organisms can originate on earth only from pre-existing life.
This theory rejected the theory of spontaneous generation but cannot explain origin of life.
To prove biogenesis and to disprove abiogenesis, experiments were performed by the following scientists–
Francesco Redi's Experiment (Italian 1668) : He took cooked meat in three jars. One was
uncovered, the second was covered with parchment and the third was air tight.
He observed that maggots developed only in the uncovered jar while maggots could not develop in the
meat in closed jars.
This proved that larvae were formed from eggs laid by the flies in open jars. Since the meat in closed jars
could not be visited by flies so no larvae could develop. Therefore, life originated from pre-existing life.
Lazzaro Spallanzani (Italian 1767) : He boiled vegetables and meat to prepare a sterilized nutritive
soup and he kept some of it in air sealed flasks and some in loosely corked flasks. He observed that
the soup in sealed flask remained sterile while micro-organisms appeared in the soup in loosely
corked flasks. Thus, even micro-organisms were formed from pre-existing ones in the air rather than
spontaneously.
Louis Pasteur (French 1862) : Pasteur is popular for germ theory of diseases or Germ theory and
he disproved abiogenesis. He prepared sterilized syrup of sugar and yeast by boiling them in flasks.
He took two flasks, one of broken neck and another of curved neck (swan neck flask). No life
appeared in swan neck flask because germ laden dust particles in the air were trapped by the curved
neck which serves as filter while in the broken neck flask colonies of micro-organism were
developed.
forms of life on earth was called bioevolution or evolutionary biology by Mayer (1970).
➢ The word evolution means to unfold or unroll or to reveal hidden potentialities. Evolution
simply means an orderly change from one condition to another.
➢ Evolution is a slow but continuous process which never stops (irreversible).
ORIGIN OF LIFE
➢ Origin of life is the process by which living organisms developed from inanimate matter
(which is generally thought to have occurred on Earth between 3800 - 4200 millions years
ago).
➢ First life evolved about. 3800-4200 million years back.
➢ There are several theories about the origin of life, like big bang theory, theory of special
creation, theory of eternity, cosmozoic theory etc.
BIG-BANG THEORY
➢ This theory was proposed by Abbe Lemaitre.
➢ According to this theory, the universe originated about 20 billion years ago due to a
thermonuclear explosion of a dense entity. This thermonuclear explosion is called Big-bang.
➢ About 4.6 billion years ago, the origin of the solar system took place by the gaseous clouds
formed due to this explosion.
➢ These gaseous clouds collapsed and converted into flat disc-like structure made up of atoms
and small particles due to their own gravitational pull. This flat-disc like structure is called Solar
Nebula.
➢The very hot central part of this solar nebula became still hotter and converted into the sun.
,➢Now, due to condensation of atoms and dust particles moving around the sun, the formation of
the other planets took place like: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus,
Neptune.
➢ The solid part of our planet earth was called lithosphere and the gaseous part was known as
atmosphere.
➢ When the earth's surface cooled down and its temperature decreased to 100° C, water formed
on it – slowly hydrogen and helium gases formed.
THEORY OF SPECIAL CREATION
➢ The greatest supporter of this theory was father Suarez.
➢ According to the Bible, life and everything was created by God in 6 days from ‘materia
prima’ & man created on 6th day.
➢ According to Hindu mythology, the world was created by God Brahma. According to it, life
has not changed ever since its origin.
➢ Special creation theory lacks scientific evidence so it is not accepted.
THEORY OF CATASTROPHISM
➢ The greatest supporter of this theory was Cuvier.
➢ According to which a gap of certain period, the world undergoes catastrophs (sudden calamity)
to kill almost all the living organisms and new life arises from inorganic matter.
, COSMOZOIC THEORY/PANSPERMIA THEORY
➢ This theory is proposed by Richter and supported by Arrhenius and Helmholtz.
➢ Protoplasm reached earth in the form of spores (pansperms) or other simple particles from
some unknown part of the universe with cosmic dust and they gave rise to various forms of life.
THEORY OF BIOGENESIS
According to this theory, new organisms can originate on earth only from pre-existing life.
This theory rejected the theory of spontaneous generation but cannot explain origin of life.
To prove biogenesis and to disprove abiogenesis, experiments were performed by the following scientists–
Francesco Redi's Experiment (Italian 1668) : He took cooked meat in three jars. One was
uncovered, the second was covered with parchment and the third was air tight.
He observed that maggots developed only in the uncovered jar while maggots could not develop in the
meat in closed jars.
This proved that larvae were formed from eggs laid by the flies in open jars. Since the meat in closed jars
could not be visited by flies so no larvae could develop. Therefore, life originated from pre-existing life.
Lazzaro Spallanzani (Italian 1767) : He boiled vegetables and meat to prepare a sterilized nutritive
soup and he kept some of it in air sealed flasks and some in loosely corked flasks. He observed that
the soup in sealed flask remained sterile while micro-organisms appeared in the soup in loosely
corked flasks. Thus, even micro-organisms were formed from pre-existing ones in the air rather than
spontaneously.
Louis Pasteur (French 1862) : Pasteur is popular for germ theory of diseases or Germ theory and
he disproved abiogenesis. He prepared sterilized syrup of sugar and yeast by boiling them in flasks.
He took two flasks, one of broken neck and another of curved neck (swan neck flask). No life
appeared in swan neck flask because germ laden dust particles in the air were trapped by the curved
neck which serves as filter while in the broken neck flask colonies of micro-organism were
developed.
