Systematics, Evolution & Zoogeography |Module 2 Unit 1 & 2 | Calicut University Third Semester BSc. Zoology Notes PDF |

 MODULE 2 : PRINCIPLES OF EVOLUTION, UNIT 1 & 2 : INTRODUCTION & THE THEORIES ON ORIGIN OF LIFE 

In this study material i have included two units from module two; which are the introductory part and the various theories on the origin of life on planet Earth.

Summary of What You Will Learn in This Study Material 

🌱 Concept of Evolution

Evolution is defined as the gradual heritable change in living organism over successive generations, leading to the formation of new species. These changes occur primarily at a genetic level through mutation, recombination, natural selection, genetic drift, and gene flow.

🌍 Organic and Inorganic Evolution

Inorganic evolution refers to the transformation of non-living Earth. This includes the formation of the oceans, mountains, atmosphere, and chemical compounds. 

Organic evolution is the gradual development of living organisms from simpler ancestral forms over a geological time. One of its fundamental features is irreversibility, once a complex form evolves it does not revert back to its primitive ancestral state.

📜 History of Evolutionary Thought

Pre-Darwinian Period:

Before 19th century most scholars believed that species were created independently and remained unchanged.

The first comprehensive evolutionary theory was proposed by Jean-Baptiste Lamarck. He suggested that evolution occurs through two principles: use and disuse of organs, and inheritance of acquired characters. According to him, organs that are frequently used becomes stronger while unused organs degenerate, and such acquired traits are transmitted to offspring. 

But August Weismann later on through his experiments disproved Lamarck's theory. 

Darwinian Period:

A major breakthrough came with Charles Darwin and Alfred Russel Wallace, who independently proposed the theory of natural selection.

Darwin’s ideas were shaped during his voyage on the HMS Beagle, where he observed variation among finches of the Galápagos Islands. He proposed that individuals with favourable variations survive and reproduce, known as natural selection.

Their joint presentation at the Linnean Society in 1858 formally introduced evolutionary theory to the scientific community. Darwin’s book On the Origin of Species (1859) later provided extensive evidence for evolution.

Post-Darwinian Period:

After Darwin evolutionary theory was strengthened by strong evidences in molecular biology and genetics. Theories such as mutation theory proposed by Hugo de Vries laid a strong foundation.  

In the twentieth century, the Modern Synthetic Theory of Evolution (Neo-Darwinism) emerged. It integrated Darwin’s natural selection with Mendelian genetics and highlighted mutation, recombination, gene flow, genetic drift, and natural selection as key mechanisms of evolution.

🌊 Oparin–Haldane Theory and Chemical Origin of Life

The question of how life originated was answered scientifically by Alexander Oparin and J. B. S Haldane . Their theory of chemical evolution proposed that life arose gradually from non-living matter through a series of chemical reactions.

According to this theory, early Earth had a reducing atmosphere composed of methane, ammonia, hydrogen, and water vapour. Under the influence of ultraviolet radiation, lightning, and volcanic activity, simple inorganic molecules formed organic compounds. Over time, these organic molecules accumulated in oceans, forming what Haldane described as the “primordial soup.”

Monomers such as amino acids and sugars polymerised to form macro molecules such as proteins and nucleic acids. These macro-molecules aggregated to form coacervates which evolved to protocells, which are ancestors of living cells.

⚡ Miller–Urey Experiment

In 1953, Stanley Miller and Harold Urey experimentally tested the Oparin–Haldane hypothesis. They simulated early Earth conditions in a closed apparatus containing methane, ammonia, hydrogen, and water vapour. Electric sparks mimicked lightning. After a week, amino acids such as glycine and alanine were detected. This experiment provided the first experimental evidence that organic molecules essential for life could be synthesised abiotically.

🦠 Evolution of Prokaryotic and Eukaryotic Cells

The earliest form of life were simple prokaryotic cells that obtained energy abiotically. Later, photosynthetic bacteria evolved and began releasing oxygen, leading to the Great Oxidation Event.

The origin of eukaryotic cells explained by the Endosymbiotic Theory, proposed by Lynn Margulis. According to this theory, mitochondria and chloroplasts originated from symbiotic prokaryotes that were engulfed by ancestral host cells. Evidence includes the presence of circular DNA, prokaryotic-type ribosomes, double membranes, and binary fission in these organelles.

📝 Important Exam Questions

• Explain the Oparin–Haldane theory with suitable stages.
• Discuss the evolution of prokaryotic and eukaryotic cells.
• State Lamarck’s theory.
• Miller–Urey experiment

You can download the complete PDF version of this unit for structured revision and offline study.

This material is created to support your academic journey, so feel free to use it for personal learning. Kindly provide credit if you share it with others.

Keywords:

Calicut university bsc zoology notes pdf free download, calicut university study material pdf free download, calicut university bsc zoology notes download, complementary zoology notes calicut university 1st sem, calicut university bsc zoology notes pdf, calicut university study material UG, calicut university notes pdf, calicut university second semester zoology notes, calicut university 2nd sem, calicut university exam dates, calicut university pareeksha bhavan, calicut university 3rd sem, calicut university third semester zoology notes,  calicut university 3rd sem