Evolution: History, Theory, Evidence, Examples

Evolution: The scientist Theodosius Dobzhansky once said, “Nothing in biology makes sense, except in the light of Evolution” This statement is still as true today as when he first said it in the 1960s. However, you may be wondering, what is evolution? Evolutionary Biology is the study of the history of life forms on earth. But to understand exactly what evolution is, we will have to understand a few different concepts.

We will have to understand the origin of life and evolution of life forms or biodiversity on our wonderful planet earth. If that seems like a lot, not to worry, because we have broken down the concepts for you in simple and easy-to-understand terms. Simply put, Evolution is changing over time that can accumulate and create the varying life forms that we see around us.

Natural selection

Charles Darwin’s book “On the Origin of Species,” published in 1859, was the first to articulate the theory of evolution through natural selection. Darwin illustrates how creatures change over generations by inheriting physical or behavioural features in his book. The theory is based on the idea that there is a variety of features within a population, such as a beak form in one of the Galapagos finches Darwin investigated.

Individuals having qualities that enable them to adapt to their settings, according to the hypothesis, will help them survive and have more offspring who will inherit those traits. Individuals that are less adaptable are less likely to live to pass on their traits.

The features that enable species to live and reproduce will grow more common in the population over time, and the population will change or evolve. Darwin proposed that genetically distinct species could originate from a common ancestor through natural selection.

Darwin was unaware of the method through which qualities were handed on, as he was unaware of genetics, the process through which genes encode specific features and how these traits are passed down from generation to generation. He also had no idea about genetic mutation, which is how natural variety is created. However, geneticists later discovered the process and added to the evidence for the theory of evolution by natural selection.

Evolution and Origin of Life

Do you think the world as we know it now has always been like this? If not, how do you think all the different life forms we see around us came about? You’re in good company. Many philosophers and scientists have pondered over these questions throughout the ages.

As we understand now, Life appeared approximately 500 million years after the earth’s formation. That was almost four billion years ago! Let’s look at a few theories that have been proposed to explain the origin of life.

1) Panspermia

Philosophers from ancient Greek proposed the idea of Panspermia. Simply put, it means that units of life called spores were transferred to different planets, including earth, which is how life first originated. While ‘Panspermia’ is still a favourite idea for some astronomers, we do not have any concrete proof for the existence of this theory.

2) Spontaneous Generation

It was thought that life came from decaying and rotting things such as straw, muck, etc. for the longest time. This was the spontaneous generation theory. Louis Pasteur established via meticulous experimentation that life could only come from pre-existing life.

He demonstrated that life did not arise from dead yeast in pre-sterilised flasks, but that new living creatures did appear from ‘killed yeast’ in an open flask. The hypothesis of spontaneous generation was finally debunked.

3) Primordial Soup/ Urey-Miller experiment

This, however, did not explain how the first life form arrived on Earth. Oparin of Russia and Haldane of England hypothesised that the initial form of life could have evolved from non-living organic molecules (e.g., RNA, protein, etc.) and that chemical evolution, i.e., the production of varied organic molecules from inorganic ingredients, came before life.

High temperatures, volcanic storms, and a decreasing atmosphere, including CH₄ and NH₃, were among the conditions on Earth. An American scientist, S.L. Miller, achieved identical conditions in a laboratory size in 1953 and observed the formation of amino acids. In similar experiments, others observed the formation of sugars, nitrogen bases, pigment and fats.

What is the Evidence for Evolution?

Many sources have provided evidence that the evolution of living forms has occurred on Earth. Fossils are the hard remains of living organisms discovered in rocks. Rocks form sediments, and a cross-section of the earth’s crust shows how sediments have accumulated one on top of the other throughout the course of the planet’s lengthy history.

Different-aged rock sediments contain fossils of various life forms that are thought to have died during sediment formation. Some of them look like current species. They are the remains of extinct species (e.g., Dinosaurs). The geological period in which fossils were found can be determined by examining them in different sedimentary strata. The study found that life forms changed with time and that some life forms are only found in specific geological time periods.

Summary

Evolutionary Biology is the study of the history of life forms on earth. Charles Darwin proposed the theory of Evolution by Natural Selection. The theory is based on the idea that there is a variety of features within a population and individuals that have qualities that enable them to adapt to their environment, survive and have more offspring who will inherit those traits. Individuals that are less adaptable are less likely to live to pass on their traits.

A few different theories for the origin of life are panspermia, spontaneous generation, and the primordial soup hypothesis. Scientists are still working on these problems, and rely on many different lines of evidence such as the fossil record, molecular biology techniques and others to constantly update our understanding of the theory of evolution

FAQs on Evolution

Students might be having many questions with respect to Evolution. Here are a few commonly asked questions and answers.

Q.1. What is the difference between Evolution and natural selection?
Ans: Evolution is the process by which the variation in the living organisms on our planet arises. Natural selection is one of the mechanisms through which evolution occurs.

Q.2. Who proposed the theory of evolution?
Ans: Charles Darwin was the scientist who proposed the theory of evolution via natural selection. Another scientist, Alfred Russel Wallace also proposed a similar theory around the same time. However, Charles Darwin presented his findings with a large amount of data that he had accumulated over many years.

Q.3. What are fossils?
Ans: Fossils are the hard remains of living organisms discovered in rocks.

Q.4. What are the different theories for the origin of life?
Ans: Panspermia, Spontaneous generation from decaying matter, and primordial soup theory are the few theories that hypothesize how life originated on our planet

Q.5. What was the experiment for the primordial soup hypothesis?
Ans: Oparin of Russia and Haldane of England hypothesised that the initial form of life could have evolved from non-living organic molecules. American scientists, Harold C. Urey and S.L. Miller, achieved identical conditions in a laboratory size in 1953 and observed the formation of amino acids.

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