Theories of Evolution

Introduction

In theories of evolution, we will take a look at different theories, evolution definitions and hypotheses about the origin of the earth and universe by philosophers and scientists. These theories will help us understand the entire journey of earth from the beginning until now. How did the earth as we know it come to be?

Early Theories of Evolution

Nebular Hypothesis

• German philosopher Immanuel Kant put forth the nebular hypothesis in his book the “Universal Natural History & Theory of the heavens” in 1755
• Mathematician Pierre-Simon Laplace re-examined the hypothesis in 1796
• The hypothesis suggested that planets were moulded from clouds of gaseous materials associated with the young sun

Revised Nebular Hypothesis

•  In 1950, Carl Weizascar of Germany and Otto Schmidt of Russia revised the hypothesis
• According to the revised nebular hypothesis, the sun is surrounded by a solar nebula made of hydrogen, helium, and dust
• As per the revised nebular hypothesis, planets were formed through the process of accretion

Binary Theories

Binary theories refer to the theories scientists and philosophers considered a companion to the sun, which would have been coexisting.  

Modern theories of Evolution

Origin of the Universe

After developing different theories on the origin of the earth, scientists and philosophers focused on the universe’s origin and developed several theories.

Big Bang Theory

The big bang theory is also called the expanding universe hypothesis. In 1920, scientist Edwin Hubble developed Hubble’s law, also known as the Hubble-Lemaitre law. Edwin Hubble observed that galaxies are gradually moving away from earth at a speed that is proportional to their distance. The big bang theory says all the matter which made the universe, existed as a ball at the beginning of the universe. According to this theory, when the big bang occurred approximately 13.7 billion years ago, the tiny ball from which the universe originated, burst fiercely and started expanding. 

Development of the Universe as per Big Bang Theory

As per the big bang theory, the universe’s development can be divided into 2 stages – at the beginning and after the big bang. This theory suggests that all matter existed in one place as a tiny ball in the beginning. This tiny ball had a small volume, infinite temperature, and infinite density. The tiny ball exploded violently during the big bang and began its expansion process. A process that continues to this day. It is assumed that there was rapid expansion after the explosion and that expansion has since slowed down.

Hoyle’s Concept of Steady State

Hoyle’s steady-state concept is an alternative to the theory of an ever-expanding universe. Hoyle’s steady-state concept considers the universe to be of the same size throughout. However, evidence has been collected that supports the theory of an expanding universe, which makes this concept unfavourable within the scientific community.

Evolution of Organisms

Different organisms adapt to different conditions to survive the changing environment. This is called evolution. Evolution in organisms can be reflected through genes, noble traits, and new species. The evolution of an organism is dependent on two major factors – genetic variability and change in geographic location over time. There are four types of evolution: divergent evolution, convergent evolution, parallel evolution and coevolution. The mechanisms through which the characteristic evolution happens in organisms are mutation, genetic drift, gene flow, non-random mating, population speciation and natural selection. Over time, evolution has led to changes in the shape and size of bones in different species to maintain natural selection. Scientists call these interchangeable parts homologous structures. 

Natural Selection Theory 

Alfred Wallace, a 19th-century British biologist, proposed the theory of evolution through natural selection. Organisms produce more offspring than they can survive in the changing environment, according to the natural selection theory. The more physically equipped and healthy an organism is, the better it is able to mature. It is also able to reproduce more offspring than those lacking in these aspects. The weaker organisms either don’t survive until the age of maturity to reproduce or reproduce very few offspring. This theory can be summarised as survival of the fittest.  

Charles Darwin’s Theory of Evolution 

The evolution through natural selection is proved by Charles Darwin’s theory. His theory states that adaptive organisms are more likely to be able to survive a changing environment. These organisms will also have higher chances of reaching the age of maturity, reproducing and passing on more evolved genes.

Conclusion

Many theories and studies have explained the evolution of the earth and the universe. A theory is an idea about something and its explanation. The theory of evolution is based on the idea that all organisms are somehow related to each other. The big bang theory is the cosmological model that proves that the evolution and existence of the whole universe happened with an explosion of atoms. The large-scale expansion of the universe began with the big bang. 

On the other hand, the steady-state theory was proposed by British scientists Sir Hermann Bondi, Thomas Gold, and Sir Fred Hoyle in 1948. Sir Fred Hoyle further developed it after complications arrived within the theory due to the big bang hypothesis. Charles Darwin’s theory of evolution, in turn, examined the evolution of living organisms. All these theories have played a major role in comprehending the evolution of the universe and the organisms inhabiting the earth.