Introduction to Evolution



Evolution is the law of life. It is the gradual change in the inherited traits of a biological population over subsequent generations. Evolutionary changes such as a change in physical appearance, mental skills, and emotional development occur as a result of the genetic variations passed through the genes. There are multiple factors involve in evolutionary science but the genetic variations play a key role. It is said that all organisms have come from a single cell. But, the question here is why some organisms are still unicellular and some are multicellular with complex structure and functions? It’s again because of the depth of variation that a particular species undergone through generations. Multiple cell differentiations in the individuals due to the influence of genes combined with mutation lead to the evolutionary process. Among all the organisms, human beings are the most evolved and highly advanced species. In other words, we are one of the oldest organisms undergone a lot of variations witnessing many variations and differentiations.


Table of Contents

1. Introduction

2. Evolution as a discipline

3. Origin of life

4. Big-bang theory

5. Formation of hydrogen and helium gases

6. Formation of the atmosphere

7. Formation of various gases

8. Formation of life or Abiogenesis

9. Oparin and Haldane concept

10. S.L. Miller`s laboratory experiment


Evolution as a discipline

Evolution is the branch of biology dealing with the study of the history of life forms on earth and how they have changed over a period. In order to understand the changes in the lives of plants and animals, one should be clear about the complete picture of the origin and evolution of the earth, sun, moon, and stars as the changes in these planetary bodies are directly or indirectly linked with the evolution of life forms.


Origin of life

It still a debate of how and when exactly the life forms had begun, however, some evidences have drawn the conclusion that this universe has begun forming 20 billion years ago. Earth is aged about 4-5 billion years. What we are witnessing today on the earth was entirely in its primitive form at once. Evolutionary changes have influenced on both living and non-living forms resulted in the modification of organisms to what we see today. For instance, the soil was formed out of rock-solid masses when the natural rain and sunlight hit against them. Some of the basic evolutionary theories are explained as under.


Big-bang theory

It was speculated that the whole universe including the earth, sun, moon, and stars were formed as a result of a single explosion of a huge solid mass. The big-bang theory postulated that a gigantic and unknown object has exploded and scattered into fragments. Each fragment has converted into small pieces. Each piece underwent a lot of changes to gain its shape, size, and structure. Hence, the earth is just a speck out of many planetary bodies. 


Formation of hydrogen and helium gases

Big-bang theory states that, after the surprise explosion, the universe has drastically expanded. Such an expansion has distributed the heat evenly across the planets resulting in the gradual dropping of core temperatures. Hydrogen and the Helium were the first of all other gases. Gradually, the gases started expanding. Hydrogen and helium are lightweight gases, they react with the heat quickly making them float higher( ozone layer)  in the atmosphere. In the next phase, gases condensed slowly to form a cool earth sphere. Big-bang theory predicted that the explosion was the main reason behind the formation of the Milky-Way galaxy. The theory also estimated that the earth is 4.5 billion years old.


Formation of the atmosphere

When the earth was formed, there was no atmosphere. However, water vapours, methane, carbon dioxide and ammonia have released out of the molten mass explosion. Such elements released out of molten mass were not conducive for the survival of creatures, so millions of years later,  the evolution of atmosphere has brought in right conditions in which we all are living today.


Formation of the atmospheric gases

The ultraviolet rays from the sun broke H2O into Hydrogen and Oxygen. In the early days of earth formation, extreme volcanism has hit the earth. Volcanoes had led to the formation of a few gases known as the volcanic gases. The mechanism involved in the formation of gases is called degassing of molten mass where the combination of 2 or more gaseous elements led to the formation of a new gas. For instance, oxygen combined with ammonia and methane to form water and CO2. As the gases evolved into an advanced form, the ozone layer was formed. Again when the ozone layer cooled, the water vapour fell as rain. Heavy rains have filled the reservoirs such as ponds, oceans etc. The picture explains how the H2O releases H+OH and hydrogen escapes from hydrolysis. 


Formation of life or Abiogenesis

Primitive lives appeared over 4-5 billion years ago. There are still so many questions about how were first life forms formed?  and they have undergone differentiation into many species, colours, classes?  Early scientists believed that life on the earth came from outside. But, the evidence suggests that the earliest known life-forms are putative fossilized microorganisms. However, this evidence couldn’t be accepted by many modern theorists.


Oparin and Haldane concept

Oparin and Haldane have proposed that the early life forms were made up of  RNA, DNA and proteins. This was preceded by chemical evolution. The chemical evolution states that a diverse number of organic molecules have formed when the inorganic constituents combine with the sunlight and volcanic storms.


S.L. Miller`s laboratory experiment

Miller has created an artificial laboratory setting in the year 1953 to demonstrate the evidence of the formation of sugars, nitrogen bases, pigments, fats, and amino acids. He created a high emission electric source in the form of a spark as shown in the picture. The electric discharge was instant and enclosed within the flask containing CH4, H2, NH3 and water vapour at 8000C. During his experiments he observed the formation of sugars, nitrogen bases, pigments,  fats, and amino acids that ensemble the gases in the atmosphere. Similar experiments were conducted further from many scientists, they also observed the same phenomenon. Based on the series of experiments and observations, the first non-cellular forms of life are assumed to be originated around 3 billion years back when the atmospheric gases were freely available. 





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