ZOOHCC - 602: Evolutionary Biology (Theory) Unit:-1
Evolution
Evolution is the process by which species of organisms change over time through the gradual accumulation of small genetic modifications that are inherited across generations. These changes in genetic makeup can result in the development of new traits, behaviors, and adaptations that can ultimately lead to the formation of new species.
The theory of evolution is based on the principles of natural selection, which was first proposed by Charles Darwin and Alfred Russel Wallace in the mid-19th century. Natural selection is a process by which certain traits become more or less common in a population depending on their usefulness in a given environment. Traits that enhance an organism's survival and reproduction are more likely to be passed on to future generations, while traits that are less advantageous are more likely to be lost over time.
Evolution occurs through several mechanisms, including mutation, gene flow, genetic drift, and natural selection. Mutations are random changes in an organism's genetic code that can produce new genetic variations. Gene flow occurs when genes are exchanged between populations, often through migration. Genetic drift is the random fluctuation of allele frequencies in a population, which can occur due to chance events. Natural selection is the main driving force behind evolution, as it allows advantageous traits to become more common over time.
Life’s Beginnings
Chemogenesis :- (Chemical Evolution Theory)
Tthe theory of chemical evolution based on chemical reactions and the
formation of matter based on chemical reactions. This theory states that
"life arises as a result of the evolution of inorganic matter." In the
1920s, scientists Opalin and Holden hypothesized that the Earth's primordial
atmosphere, containing substances such as methane, ammonia, and water, was
the chemical origin of life. Oxygen concentrations were very low due to the
high temperature of 5000-6000 °C. So these conditions are not suitable for
the free existence of organic compounds and hence the reaction took place.
Inorganic substances change into inorganic compounds under conditions such
as strong sunlight and heat. And this can lead to an increasingly
concentrated reservoir of organic compounds over millions of years.These
connections interact to create life. Chemogenesis, therefore, is the process
of chemical evolution of the Earth, the formation of life from pre-existing
matter through chemical reactions.
In the 1920s, Russian biochemist Alexander Oparin proposed that life
on Earth originated from a "primordial soup" of organic molecules that
formed spontaneously in the Earth's early atmosphere. British scientist
J.B.S. Haldane later expanded on this idea, suggesting that the energy from
lightning and ultraviolet radiation could have helped to drive the formation
of complex organic molecules.
In 1953, American chemists Stanley Miller
and Harold Urey performed an experiment that demonstrated the plausibility
of the Oparin-Haldane hypothesis. They created a closed system that
simulated the primitive Earth's atmosphere, consisting of methane, ammonia,
water vapor, and hydrogen. They then subjected this mixture to electrical
discharges to simulate lightning. After just a few days, they observed the
formation of amino acids, which are the building blocks of proteins.
Miller-Urey
experiment
The Miller-Urey experiment was a classic experiment performed by
Stanley Miller and Harold Urey in 1952 to test the Oparin-Haldane theory of
chemical evolution. The experiment was designed to simulate the conditions
of Earth's early atmosphere and test whether organic compounds could be
produced from inorganic materials by natural processes.
In their experiments, Miller and Urey created a closed system
consisting of flasks containing water, methane, ammonia and hydrogen. They
were thought to be the main constituents of the early Earth's atmosphere.
They heated the mixture to produce steam and then passed an electrical
discharge through the mixture to simulate lightning, thought to be common in
the early Earth's atmosphere.
After a week of continuous operation, the researchers analyzed the contents
of the flask and discovered a variety of organic compounds, including amino
acids, the building blocks of proteins. This experiment shows that the
formation of organic compounds from inorganic materials can occur under
conditions prevailing on the early Earth, supporting the idea of the
chemical theory of evolution.
The Miller-Urey experiment was a key experiment in the study of the
origin of life, and influenced many subsequent studies on the origin of life
and the role of chemical evolution in the origin of life on Earth.
RNA world:-
The RNA world is a hypothetical stage in the early evolution of life on
Earth, in which RNA (ribonucleic acid) molecules played a central role as
both genetic material and catalysts for chemical reactions. According to
this theory, RNA was the precursor to DNA and proteins, which are the
building blocks of all living organisms.
The RNA world hypothesis suggests that in the primordial soup of the
early Earth, there were organic compounds that spontaneously formed RNA
molecules. These RNA molecules could replicate themselves and undergo
mutations, which led to the emergence of new RNA sequences with different
properties. Over time, some RNA molecules evolved the ability to catalyze
chemical reactions, including the synthesis of other RNA molecules.
The RNA world hypothesis is supported by several lines of evidence,
including the ability of some RNA molecules to catalyze chemical reactions,
the discovery of ribozymes (RNA molecules with enzymatic activity), and the
observation that RNA can store genetic information and undergo
self-replication.
While the RNA world hypothesis is still an active
area of research, it is widely accepted as a plausible scenario for the
origins of life on Earth.
The term "primordial soup" was coined by the British biologist J.B.S.
Haldane in the 1920s. He suggested that the early Earth's atmosphere was
reducing, meaning it lacked oxygen, and was rich in methane, ammonia, and
other gases. These gases were exposed to energy sources such as lightning
strikes, volcanic activity, and ultraviolet radiation from the sun. As a
result, organic compounds were synthesized, which then dissolved in the
oceans, creating a "soup" of organic molecules.
Biogeny:- (biogenesis)
Biogenesis is the principle that living organisms arise from other living
organisms, and not from non-living matter. This idea was first proposed in
the 17th century by the Italian physician Francesco Redi, who conducted
experiments to show that maggots only appear on decaying meat when flies
have access to it. Later experiments by Louis Pasteur in the 19th century
further supported the principle of biogenesis, showing that microorganisms
do not arise spontaneously in sterilized solutions but only from
pre-existing microorganisms.
The principle of biogenesis is important
in the study of evolution because it provides evidence for the common
ancestry of all living organisms. All living organisms share a common
ancestor, and the diversity of life on Earth has arisen through a process of
descent with modification from that ancestor.
The principle of biogenesis also refutes the idea of spontaneous
generation, which was the belief that living organisms could arise from
non-living matter. This idea was widely accepted in ancient times but was
discredited by the experiments of Redi and Pasteur, which showed that living
organisms can only come from pre-existing living organisms.
Pasture's Experiment:-
Louis Pasteur conducted several experiments in the 19th century that
provided evidence for the principle of biogenesis and helped to disprove the
theory of spontaneous generation. One of his most famous experiments
involved sterilizing broth in a specially designed flask with a long curved
neck that allowed air to enter but prevented dust and microorganisms from
getting into the broth.
Pasteur then observed that the broth remained
free of microorganisms, even though it was exposed to the air. This
experiment showed that microorganisms do not arise spontaneously in
sterilized solutions, but only from pre-existing microorganisms that are
introduced from the outside.
Another experiment involved heating wine to a high temperature to
kill off any microorganisms present, and then sealing the wine in airtight
bottles. Pasteur observed that the wine remained clear and did not develop
any sour taste or cloudiness, which would have indicated the growth of
microorganisms. This experiment helped to establish the process of
pasteurization, which involves heating a liquid to a high temperature to
kill off any harmful microorganisms.
Pasteur's experiments provided important evidence for the principle
of biogenesis and helped to discredit the theory of spontaneous
generation (Abiogenesis), which was widely accepted at the time. These
experiments also had important practical applications in the development of
sterilization techniques and the prevention of food spoilage.