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.
