TG: @Chalnaayaaar
01 Evolution
1. Introduction :
What is Evolution?
• The word evolution means to unfold or unroll or to reveal hidden potentialities. Evolution simply
means an orderly change from one condition to another.
• It can be best explained by Darwin's concept of 'Descent with modification'.
(A) Evolutionary Biology :
• It is the study of history of life forms i.e. the changes in flora and fauna that have occurred over
millions of years on earth.
• To understand the changes in flora and fauna that have occurred over millions of years on earth,
we must have an understanding of the context of origin of life, i.e., evolution of earth, of stars and
indeed of the universe itself.
• What follows is the longest of all the construed and conjectured stories. This is the story of origin
of life and evolution of life forms or biodiversity on planet earth in the context of evolution of earth
and against the background of evolution of universe itself.
What is Universe?
• The universe is a huge cluster of galaxies. Galaxies contain stars and clouds of gas and dust.
Considering the size of universe, earth is indeed a speck i.e. The universe is vast. So vast that the
stellar distances are measured in light years.
• When we look at stars on a clear night sky we are, in a way, looking back in time. What we see today
is an object whose emitted light started its journey millions of years back and from trillions of
kilometres away and reaching our eyes now. However, when we see objects in our immediate
surroundings, we see them instantly and hence in the present time. Therefore, when we see stars,
we apparently are peeping into the past.
• The Big Bang theory attempts to explain to us the origin of universe.
TG: @Chalnaayaaar
Digital www.allendigital.in [3]
, TG: @Chalnaayaaar
NEET : Biology
(B) Big Bang Theory- Proposed by Abbe Lemaitre :
• According to it, the universe originated about 20 billion
years ago due to a thermonuclear explosion of a dense
entity. This single huge explosion, which is unimaginable
in physical terms, is called as big bang.
• The universe expanded and hence, the temperature
came down. Hydrogen and Helium were formed
sometime later.
• The gaseous clouds which were formed by the big bang
condensed under gravitation and converted into many
flat discs like structures called nebula, made up of atoms
and small particles. Solar nebula was one of them,
which formed our solar system.
• The very hot central part of solar nebula became even
hotter due to pressure and converted into the sun.
• Later, due to condensation of atoms and dust particles
moving around the sun, planets were formed.
• In the solar system of the Milky Way galaxy, earth was
supposed to have been formed about 4.5 billion years
back.
• There was no atmosphere on early earth. It was
formed later.
(C) Primitive Earth :
• There was no atmosphere on early earth but later, water vapour, methane, carbon dioxide and
ammonia released from molten mass covered the surface.
• All the oxygen present at that time, combined with ammonia and methane to form water, CO 2 and
others. As it cooled, the water vapor fell as rain, to fill all the depressions and form oceans.
• The conditions on earth were – high temperature, volcanic storms, lightening, unstable radioactive
elements, UV rays, reducing atmosphere containing CH4, NH3, etc.
• Life appeared 500 million years after the formation of earth, i.e., almost four billion years
back.
• The UV rays from the sun broke up water into Hydrogen and Oxygen and the lighter H2 escaped.
• The ozone layer was formed.
TG: @Chalnaayaaar
[4] www.allendigital.in Digital
, TG: @Chalnaayaaar
Evolution
2. Theories for Origin of Life :
(A) Theory of Special Creation :
• The greatest supporter of this theory was Father Suarez. This is a mythology-based theory.
• This theory has three connotations-
o All living organisms (Species or types) that we see today were created as such.
o The diversity was always the same since creation and will be the same in future.
o The earth is about 4000 years old.
• All these ideas were strongly challenged during the nineteenth century based on observations of
Charles Darwin, Wallace etc. They believed that life forms varied over the periods of time.
• From fossils records and their dating, we can conclude that earth is very old, not thousands of years
as was thought earlier but billions of years old.
(B) Cosmic Panspermia Theory :
• Some scientists believe that life came from outer space. Early Greek
thinkers thought units of life called spores were transferred to
different planets including earth.
• 'Panspermia' is still a favourite idea for some astronomers.
(C) Theory of Spontaneous Generation (Abiogenesis/Autogenesis) :
• For a long time, it was also believed that the life came out of decaying and rotting matter like straw,
mud, etc. spontaneously.
• This hypothesis was supported by ancient Greek philosophers. They believed that the mud of river
Nile could give rise to fishes, frogs, crocodiles etc when warmed by light rays.
• Louis Pasteur by careful experimentation demonstrated that life comes only from pre-existing life
and not from dead matter.
(D) Theory of Biogenesis :
• Proposed by Harvey & Huxley They stated "Omnis vivum ex ovo or vivo", which means "New life
can originate from pre-existing life."
• Experiments of Francesco Redi, Lazzaro Spallanzani, and Louis Pasteur etc supported the
theory of biogenesis and disproved the abiogenesis. Experiment of Louis Pasteur is most renowned
among all of these.
• However, this theory did not answer how the first life-form came on earth.
Louis pasteur's swan neck flask experiment :
• Louis Pasteur prepared sterilized syrup of sugar and killed yeast by boiling them in flasks.
• He took two flasks, one of broken neck and another of curved neck (swan neck flask / "S" shaped
neck flask).
• He showed that in pre-sterilized swan neck flasks, life did not come from killed yeast because germ
laden dust particles in the air were trapped by the curved neck which serves as filter.
• However, in another flask open to air (broken neck), new living organisms arose.
TG: @Chalnaayaaar
Digital www.allendigital.in [5]
, TG: @Chalnaayaaar
NEET : Biology
Microorganisms
Broken neck
swan neck in atmosphere
flask steam
Air
yeast & sugar
solution bacteria
(sterilized) present
burner No bacteria
Louis Pasteur's swan neck flask experiment
(E) Oparin - Haldane Theory (Modern Theory) :
• Oparin of Russia and Haldane of England proposed that the first form of life could have come from
pre-existing non-living organic molecules (e.g. RNA, protein, etc.) and that formation of life was
preceded by chemical evolution, i.e., formation of diverse organic molecules from inorganic
constituents.
• Oparin's theory was published in his book 'ORIGIN OF LIFE'.
• First life originated in sea water, so water is essential for origin of life.
• Oparin-Haldane theory is studied in two parts – Chemogeny & Biogeny.
Chemical Evolution (Chemogeny) :
• Early earth had free atoms of all those elements which are essential for formation of protoplasm
(C, H, O, N etc.) Hydrogen was maximum among all of them.
• Due to high temperature hydrogen reacted with oxygen to form water and no free oxygen was left,
which made the atmosphere reducing. Hydrogen also reacted with nitrogen and formed ammonia.
• Hence, water and ammonia were probably the first inorganic compounds formed on earth.
Methane (CH4) was the first organic compound.
• As the earth cooled down, the water vapour fell as torrential rain, to fill all the depressions and
form primitive oceans. Meanwhile, molecules continued to react with each other and formed
various simple and complex organic compounds.
• Now, the water of oceans became a rich mixture of macromolecules/ complex organic compounds.
Haldane called it Hot dilute soup/ pre-biotic soup.
• Hence, the possibilities of life were established in the water of primitive oceans because these
macromolecules (Proteins, polysaccharides, fats/lipids, nucleic acids) form the main components
of protoplasm.
• However, we have no clear idea about how the first self-replicating metabolic capsule of life arose,
but we consider it to be a result of some mutations in the nucleic acids.
TG: @Chalnaayaaar
[6] www.allendigital.in Digital
01 Evolution
1. Introduction :
What is Evolution?
• The word evolution means to unfold or unroll or to reveal hidden potentialities. Evolution simply
means an orderly change from one condition to another.
• It can be best explained by Darwin's concept of 'Descent with modification'.
(A) Evolutionary Biology :
• It is the study of history of life forms i.e. the changes in flora and fauna that have occurred over
millions of years on earth.
• To understand the changes in flora and fauna that have occurred over millions of years on earth,
we must have an understanding of the context of origin of life, i.e., evolution of earth, of stars and
indeed of the universe itself.
• What follows is the longest of all the construed and conjectured stories. This is the story of origin
of life and evolution of life forms or biodiversity on planet earth in the context of evolution of earth
and against the background of evolution of universe itself.
What is Universe?
• The universe is a huge cluster of galaxies. Galaxies contain stars and clouds of gas and dust.
Considering the size of universe, earth is indeed a speck i.e. The universe is vast. So vast that the
stellar distances are measured in light years.
• When we look at stars on a clear night sky we are, in a way, looking back in time. What we see today
is an object whose emitted light started its journey millions of years back and from trillions of
kilometres away and reaching our eyes now. However, when we see objects in our immediate
surroundings, we see them instantly and hence in the present time. Therefore, when we see stars,
we apparently are peeping into the past.
• The Big Bang theory attempts to explain to us the origin of universe.
TG: @Chalnaayaaar
Digital www.allendigital.in [3]
, TG: @Chalnaayaaar
NEET : Biology
(B) Big Bang Theory- Proposed by Abbe Lemaitre :
• According to it, the universe originated about 20 billion
years ago due to a thermonuclear explosion of a dense
entity. This single huge explosion, which is unimaginable
in physical terms, is called as big bang.
• The universe expanded and hence, the temperature
came down. Hydrogen and Helium were formed
sometime later.
• The gaseous clouds which were formed by the big bang
condensed under gravitation and converted into many
flat discs like structures called nebula, made up of atoms
and small particles. Solar nebula was one of them,
which formed our solar system.
• The very hot central part of solar nebula became even
hotter due to pressure and converted into the sun.
• Later, due to condensation of atoms and dust particles
moving around the sun, planets were formed.
• In the solar system of the Milky Way galaxy, earth was
supposed to have been formed about 4.5 billion years
back.
• There was no atmosphere on early earth. It was
formed later.
(C) Primitive Earth :
• There was no atmosphere on early earth but later, water vapour, methane, carbon dioxide and
ammonia released from molten mass covered the surface.
• All the oxygen present at that time, combined with ammonia and methane to form water, CO 2 and
others. As it cooled, the water vapor fell as rain, to fill all the depressions and form oceans.
• The conditions on earth were – high temperature, volcanic storms, lightening, unstable radioactive
elements, UV rays, reducing atmosphere containing CH4, NH3, etc.
• Life appeared 500 million years after the formation of earth, i.e., almost four billion years
back.
• The UV rays from the sun broke up water into Hydrogen and Oxygen and the lighter H2 escaped.
• The ozone layer was formed.
TG: @Chalnaayaaar
[4] www.allendigital.in Digital
, TG: @Chalnaayaaar
Evolution
2. Theories for Origin of Life :
(A) Theory of Special Creation :
• The greatest supporter of this theory was Father Suarez. This is a mythology-based theory.
• This theory has three connotations-
o All living organisms (Species or types) that we see today were created as such.
o The diversity was always the same since creation and will be the same in future.
o The earth is about 4000 years old.
• All these ideas were strongly challenged during the nineteenth century based on observations of
Charles Darwin, Wallace etc. They believed that life forms varied over the periods of time.
• From fossils records and their dating, we can conclude that earth is very old, not thousands of years
as was thought earlier but billions of years old.
(B) Cosmic Panspermia Theory :
• Some scientists believe that life came from outer space. Early Greek
thinkers thought units of life called spores were transferred to
different planets including earth.
• 'Panspermia' is still a favourite idea for some astronomers.
(C) Theory of Spontaneous Generation (Abiogenesis/Autogenesis) :
• For a long time, it was also believed that the life came out of decaying and rotting matter like straw,
mud, etc. spontaneously.
• This hypothesis was supported by ancient Greek philosophers. They believed that the mud of river
Nile could give rise to fishes, frogs, crocodiles etc when warmed by light rays.
• Louis Pasteur by careful experimentation demonstrated that life comes only from pre-existing life
and not from dead matter.
(D) Theory of Biogenesis :
• Proposed by Harvey & Huxley They stated "Omnis vivum ex ovo or vivo", which means "New life
can originate from pre-existing life."
• Experiments of Francesco Redi, Lazzaro Spallanzani, and Louis Pasteur etc supported the
theory of biogenesis and disproved the abiogenesis. Experiment of Louis Pasteur is most renowned
among all of these.
• However, this theory did not answer how the first life-form came on earth.
Louis pasteur's swan neck flask experiment :
• Louis Pasteur prepared sterilized syrup of sugar and killed yeast by boiling them in flasks.
• He took two flasks, one of broken neck and another of curved neck (swan neck flask / "S" shaped
neck flask).
• He showed that in pre-sterilized swan neck flasks, life did not come from killed yeast because germ
laden dust particles in the air were trapped by the curved neck which serves as filter.
• However, in another flask open to air (broken neck), new living organisms arose.
TG: @Chalnaayaaar
Digital www.allendigital.in [5]
, TG: @Chalnaayaaar
NEET : Biology
Microorganisms
Broken neck
swan neck in atmosphere
flask steam
Air
yeast & sugar
solution bacteria
(sterilized) present
burner No bacteria
Louis Pasteur's swan neck flask experiment
(E) Oparin - Haldane Theory (Modern Theory) :
• Oparin of Russia and Haldane of England proposed that the first form of life could have come from
pre-existing non-living organic molecules (e.g. RNA, protein, etc.) and that formation of life was
preceded by chemical evolution, i.e., formation of diverse organic molecules from inorganic
constituents.
• Oparin's theory was published in his book 'ORIGIN OF LIFE'.
• First life originated in sea water, so water is essential for origin of life.
• Oparin-Haldane theory is studied in two parts – Chemogeny & Biogeny.
Chemical Evolution (Chemogeny) :
• Early earth had free atoms of all those elements which are essential for formation of protoplasm
(C, H, O, N etc.) Hydrogen was maximum among all of them.
• Due to high temperature hydrogen reacted with oxygen to form water and no free oxygen was left,
which made the atmosphere reducing. Hydrogen also reacted with nitrogen and formed ammonia.
• Hence, water and ammonia were probably the first inorganic compounds formed on earth.
Methane (CH4) was the first organic compound.
• As the earth cooled down, the water vapour fell as torrential rain, to fill all the depressions and
form primitive oceans. Meanwhile, molecules continued to react with each other and formed
various simple and complex organic compounds.
• Now, the water of oceans became a rich mixture of macromolecules/ complex organic compounds.
Haldane called it Hot dilute soup/ pre-biotic soup.
• Hence, the possibilities of life were established in the water of primitive oceans because these
macromolecules (Proteins, polysaccharides, fats/lipids, nucleic acids) form the main components
of protoplasm.
• However, we have no clear idea about how the first self-replicating metabolic capsule of life arose,
but we consider it to be a result of some mutations in the nucleic acids.
TG: @Chalnaayaaar
[6] www.allendigital.in Digital
