Theory of Evolution: How Life Originated on Earth

Life began on Earth about 4 billion years ago. After billions of years of evolution, numerous species of plants and animals evolved, including humans, Homo Sapiens. However, some people question the theory of evolution and ask why apes still exist if humans evolved from them. This article aims to explore the theory of evolution, whether it is a fact or just a mere theory, and how different types of animals evolved. Here is the complete and detailed article on Theory of Evolution.

Misconception about the Theory of Evolution:

Let’s start by clearing up the biggest misconception regarding the theory of evolution. It does not propose that monkeys evolved into humans. Rather, it suggests that all chimpanzees, gorillas, monkeys, and humans have the same ancestor, who is now extinct. To help you visualize this, imagine a tree. At first, it has only one stem, which then grows branches and smaller branches. As it continues to grow, the tips of the tree represent all the living creatures that exist today. However, you may wonder why some of our ancestors evolved into humans, while others became chimpanzees or monkeys. The answer to this question will be explained later in this article.

“On the Origin of Species”: A Book by Charles Darwin

In 1859, Charles Darwin wrote a groundbreaking book titled ‘On the Origin of Species’. In this book, he introduced the theory of “natural selection.” When you hear this term, you might think it sounds complicated or mystical. However, it is actually quite simple. Every time reproduction occurs, whether it is in humans, animals, trees, or plants, genes are passed on to the next generation. Genes carry with them certain mutations or variations, which can be beneficial or harmful depending on the environment. For instance, if you have brown eyes and your children have green eyes, that means a mutation has occurred in their genes, affecting the eye color. It is possible that the next generation of their children will also have green eyes.

Process of Natural Selection:

The process of natural selection occurs when some variations are more advantageous than others in a given environment. Those who possess advantageous variations are more likely to survive and reproduce, passing on their beneficial traits to their offspring. On the other hand, those with less advantageous variations are less likely to survive and reproduce, leading to the extinction of those traits. This simple process is what drives natural selection, which is the key mechanism behind evolution.

Let’s consider an example of a brown frog that lives in a jungle and has five children. Four of the five children are brown in colour, while one is green. The green frog can easily blend in with the green trees and thus has an advantage over the brown frogs. One day, a predator comes and eats the brown frogs that are easily visible, but the green frog is not spotted and remains safe. As a result, its descendants are also green in colour. This is a classic example of how the theory of natural selection works.

There is a commonly-used term, ‘Survival of the Fittest.’ Unfortunately, many motivational speakers misuse this term by suggesting that only physically fit individuals will survive. People often imagine that only those with big muscles and six-pack abs will be able to withstand the test of Natural Selection. However, this is incorrect. Being ‘fit’ does not refer to being the largest or most powerful. According to Charles Darwin, being ‘fit’ refers to the ability to fit well within the environment around you. This includes the climate and temperature, as well as the plants and animals in the area. The fittest individual is the one who is best suited to the situation.

Whether an individual is considered ‘fit’ or not can change over time. During the dinosaur era, some animals evolved to be huge as it protected them against predators. However, when food was scarce, being fit meant becoming smaller to reduce the food requirement. Consequently, some animals evolved to be smaller in size. Similarly, some animals evolved to have more hair on their bodies to improve insulation in cold weather. For example, polar bears have thick fur, which helps them stay warm in chilly temperatures. On the other hand, humans evolved to have less body hair, making it easier to regulate their body temperature in the summer. This allows us to sweat easily, which helps cool down the body.

How Evolution Happened?

Let’s learn about how evolution happened. Imagine a big tree, where each branch represents a different species. If we go back in time along the branches, we will find that every species has a common ancestor with another one. For example, humans and monkeys share a common ancestor, the same goes for cows and buffaloes. It’s amazing to think that all animals, trees, and plants have a common ancestor, too. This happened about 4 billion years ago when life first emerged in the water covering the Earth. Back then, the Earth was vastly different. There were no continents, and the planet was mostly covered in water.

FUCA (First Universal Common Ancestor) and LUCA (Last Universal Common Ancestor):

Scientists have named the first organism the First Universal Common Ancestor, or FUCA for short. At that time, there were no genes or DNA. Instead, free-floating nucleotides assembled into an RNA that created a molecule called PTC, which then self-organized to form FUCA. Although the first ancestor for all of us was not a cell, today we call cells the building blocks of life. However, since FUCA was not a cell, it is difficult to determine whether it was living or non-living. It is similar to a virus which is not classified as either living or non-living since it cannot grow or reproduce independently unless it is inside a host’s body.

3.8 billion years ago, FUCA evolved into a unicellular organism, which we now call LUCA (Last Universal Common Ancestor). All living things on Earth, including trees, plants, animals, bacteria, and fungi, have a common ancestor – LUCA. Scientists believe that LUCA was a prokaryotic microbe with a cell membrane, which means it did not have a proper nucleus in the cell. Researchers have estimated that LUCA has about 355 genes, all of which are found in every organism living on Earth today. This discovery was made in July 2016 by William Martin of the University of Dusseldorf.

Scientists have also discovered that viruses must have started evolving either before LUCA or they must have started co-evolving with LUCA because viruses have played a crucial role in evolution from the very beginning. In October 2016, four months after the discovery of LUCA’s genes, scientists created the smallest synthetic cell that can survive and reproduce independently in a laboratory. This synthetic cell has 473 genes, more than LUCA’s 355 genes. Therefore, LUCA is classified as half-alive, not properly living.

LUCA (Last Universal Common Ancestor) Evolution:

Although the COVID-19 virus has caused chaos, viruses have played a crucial role in our survival. LUCA, the Last Universal Common Ancestor, was the earliest known organism that reproduced through cell division. After millions of years, LUCA evolved into two separate microorganisms: Bacteria and Archaea. Despite their similarities, they differ slightly in terms of the cell wall and plasma membrane. Billions of years later, a special type of bacteria emerged – Cyanobacteria – which was capable of photosynthesis. This process involved using sunlight to generate energy by using water as fuel and oxygen as the end product. When many Cyanobacteria used photosynthesis, it led to a significant amount of oxygen being released into the air, leading to the Great Oxygenation Event.

This event took place 2.2 billion years ago. Evolution then stepped in to protect the DNA by forming the nucleus in the cell, which kept the DNA safe inside the cell. Furthermore, evolution resulted in some types of Cyanobacteria transforming into chloroplasts in the cytoplasm, which led to the birth of the plant kingdom.

Aerobic Respiration:

In the past, ancient bacteria discovered a surplus of oxygen in the atmosphere and began using it to generate energy. This marked the beginning of Aerobic Respiration. This bacteria evolved further and formed Mitochondria, which are now known as a cell’s powerhouse and an important element in all eukaryotes. Later on, these eukaryotes branched into three sub-branches: the animal kingdom, fungi kingdom, and algae kingdom (also known as Protista). This is when the Tree of Life began to take shape. Initially, there were three branches: bacteria, eukaryotes, and archaea. Then, eukaryotes branched into plants, animals, fungi, and algae. Scientists are still debating whether the Eukaryotes originated from Archaea or if Archaea and Eukaryotes are two separate branches with a common ancestor.

Despite the fact that we often associate evolution with monkeys evolving into humans, it’s important to remember that the history of evolution began with bacteria and microorganisms. In fact, only 43% of the cells in our body are human cells. The rest are bacteria, viruses, fungi, and RKI cells. Multicellular life was born about 900 million years ago because it was easier for cells to survive in groups, rather than being unicellular and alone. This is why we see multicellular organisms today.

Ikaria Wariootia:

Around 555 million years ago, there was a tiny organism called the Ikaria Wariootia, which is considered the common ancestor of all animals. It was a bilateral worm with a front and back end, meaning it had vertical or horizontal symmetry with both sides being similar. Although there are a few exceptions, such as starfish, all animals are bilateral. These fossils were found in South Australia and were carbon-dated to be 555 million years old. This makes it the oldest organism ever discovered and the ancestor of all animals.

After the Ikaria Wariootia, vertebrates or animals with spines started to develop. Fishes, reptiles, birds, and mammals are all considered vertebrates because they have a spine. The first spine was developed 480 million years ago by a fish called Arandaspis. Following this, organisms began to evolve to have four legs. Animals with four legs are called tetrapods, and this development happens in water.

Eusthenopteron:

We have yet to reach the part of the story where we come up on land. 375 million years ago, a fish called Eusthenopteron lived. It was a 6-foot-long fish with a strong jaw and sharp teeth. This fish is considered the link between all fish and land vertebrates, but it did not move to land due to fear, as evolution does not work that way.

Tiktaalik Roseae:

In 2004, Tiktaalik Roseae was discovered. Its big forefins allowed it to live on land, but realistically, it must have been living in a shallow ocean. Due to climate changes, the ocean receded, and it was forced to stay on land, where it was able to survive. Its skull was similar to a crocodile’s, which allowed it to bite and eat prey. However, not all organisms moved from water to land, as evolution does not have a linear progression. It can happen in all directions.

Qikiqtania Wakei:

Qikiqtania Wakei, a relative of Tiktalik, is believed to have come to land but couldn’t adapt and returned to the sea. Similarly, some organisms came to land but went back to the sea for further evolution, such as whales and dolphins. Unlike fish, whales and dolphins are mammals and are more closely related to humans. They cannot breathe underwater and must come to the surface to breathe. This means that dolphins and humans must have had a common ancestor who lived on land. Some of their descendants stayed on land, while others returned to the sea.

Amphibians:

Around 368 million years ago, amphibians began to evolve. Amphibians, such as frogs and salamanders, have the ability to live both in water and on land. From this branch, reptiles evolved and included species such as snakes, turtles, alligators, crocodiles, and lizards. Dinosaurs eventually evolved from this line, and they first appeared around 230 million years ago.

Brasilodon Quadrangularis:

Approximately 225 million years ago, there was a small animal that resembled a mouse and was about 20 cm long. It is called Brasilodon Quadrangularis and is now recognized as the world’s oldest mammal. Its discovery occurred only last year. The previous belief was that the Morganucodon, which lived 205 million years ago, was the oldest mammal. However, Morganucodon used to lay eggs, which is interesting because mammals are known for feeding on their mother’s milk. Humans, monkeys, dogs, cats, tigers, lions, and many other animals belong to the mammal category.

Monotremes:

Most mammals do not lay eggs, with the exception of a group called monotremes. There are currently five species of monotremes, including the platypus. Platypus fossils date back as far as 120 million years ago and they are considered one of the oldest living animals. Along with monotremes, there are two other groups of mammals: placentals and marsupials. Placental mammals, like humans, develop their babies in the womb while marsupials, like kangaroos and koalas, carry their young in a pouch. All three groups are classified as mammals because the babies drink their mother’s milk. Monotremes diverged from other mammals 166 million years ago, followed by marsupials and placental mammals 125 million years ago.

1. Marsupials:

Around 40 million years ago, the continents of South America, Antarctica, and Australia were connected, allowing marsupials to evolve and spread across these three continents. At that time, Antarctica had a forest and no ice. Today, marsupials are only found on these three continents, with most of them found in Australia. This is because, in Australia, marsupials did not face competition from other mammals, while in South America, they couldn’t compete with other mammals. This is why animals like kangaroos and koalas are only found in Australia.

2. Placental:

The oldest known placental mammal fossil, Eomaia, was found in northeast China and dates back to 125 million years ago. However, a 2013 study challenged this, stating that Eomaia did not have all the features of modern placental mammals. Instead, Maureen O’Leary and her colleagues suggested that the first placental mammal was found only 65 million years ago and looked like a rat.

The extinction of the dinosaurs paved the way for mammals to dominate the Earth’s ecosystem. A study published in the Science Journal has shown that the boom in placental mammals began only after the dinosaurs went extinct. Without this extinction event, we would never have seen the diversity in placental mammals that we see today, and humans would never have existed.

Placental Mammal Branches:

• Ungulate Group: Around 40 million years ago, the Indian continental plate collided with Asia, leading to the formation of the Himalayan Mountains. During the same period, placental mammals diverged into various branches, one of which was the Ungulate group. This group comprises several mammals with hooves, such as cows, buffaloes, pigs, goats, camels, deer, and hippopotamus. Later, the Ungulate group was further divided into two subgroups: the even-toed and odd-toed ungulates. Some animals have an even number of toes, while others have an odd number of toes. For instance, donkeys, horses, zebras, and rhinoceros are some of the odd-toed ungulates, while the rest of the examples fall under the even-toed ungulates.
• Carnivore Order: Apart from the Ungulate group, another branch of the Carnivore Order was formed, which includes carnivorous placental mammals like dogs, cats, lions, tigers, and hyenas. Interestingly, whales and dolphins are categorized as Cetaceans, and their closest ancestry is with Ungulates. In other words, whales and dolphins are closely related to cows and buffaloes. Additionally, there is a category called Afrotheria, which includes elephants and a small animal known as Hyrax. Evolution can be surprising since it doesn’t happen linearly. It happens in every direction wherever it fits. That’s why a big animal like an elephant and a small animal like a Hyrax can belong to the same category and have the same ancestor.

Reasons behind Evolution: Four Forces of Evolution

There are four main forces that drive evolution, known as the Four Forces of Evolution. I have already explained two of them.

1. Genetic Mutation: (Already Discussed Above)

The replication of DNA can cause gene mutations due to mistakes during reproduction or external factors, like ultraviolet light, which can lead to skin cancer.

2. Natural Selection: (Already Discussed Above)

The process of evolution through natural selection occurs as the genes that are best adapted to the ecosystem continue to evolve.

3. Genetic Drift:

Basically, imagine a massive explosion that radically alters the environment and everything in it. This type of event is termed a bottleneck effect or Genetic Drift. For instance, if a particular animal species is only found on a specific island, and a volcano erupts on that island, that animal will be destroyed, and its subspecies may survive on a nearby island. After the volcanic disaster, the surviving subspecies will get a chance to thrive. In the future, this subspecies will be found everywhere, and this is the bottleneck effect.

North American Bison were once found everywhere in America, but humans hunted them to extinction. However, a subspecies of bison called Plains Bison survived in Yellowstone National Park. When conservation programs were started to save it, the bison population regrew. The population was entirely made up of this subspecies. This became a bottleneck event, leading to genetic drift, and all bison in America today belong to this subspecies.

Another type of genetic drift is the “Founder Effect.” A good example of this can be seen among humans, too. The Amish people are a small community living in America and Canada. Their population is around 250,000 people, and their ancestors came from Germany and Switzerland around 200 years ago. Interestingly, only around 200 people migrated to America and Canada, and they never married outsiders. The result is that for the population of these 250,000 Amish people, their ancestors were among those 200 emigrants.

However, Charles Darwin warned that reducing genetic diversity is not good for evolution. One of the original founders was a person with a recessive gene causing the Ellis-van Creveld syndrome. Since the community kept intermarrying within themselves, this recessive gene kept being passed on. Due to evolution, today, this disease is found more among Amish people than any other species globally. Therefore, according to theory of evolution, genetic diversity is always better. To avoid intermixing in different types of genes.

4. Gene Flow:

Gene Flow is similar to genetic drift, but in this case, a population migrates to another population, and there is a mixing between the two. For instance, the insecticide resistance gene found in African malaria mosquitoes was originally found in some other species of mosquito. However, when the population of that mosquito came into contact with the African mosquitoes, they passed on this insecticide resistance gene. You may be wondering about the timeline of evolution.

How fast or slow is evolution? There is no definitive answer to this question since it depends on the species. Evolution can take millions of years, as we saw in the case of mammals. However, it can also occur in a year or two, as demonstrated by the coronavirus. The SARS-CoV-2 virus has gone through numerous mutations since the COVID-19 pandemic began, including the Delta variant and the Omicron variant. What else could it be if not evolution? As a result, it is surprising that some individuals still do not believe in theory of evolution.

Conclusion:

Theory of Evolution: Evolution is not just a mere theory, it is a fact. When we talk about a scientific theory, it means that it is made only when there is ample evidence. Albert Einstein’s Theory of Special Relativity, the Theory of the Big Bang, and the Theory of Evolution are known as theories, but they are indeed facts.

In this article, you have read about the irrefutable evidence that proves theory of evolution. There is no evidence that counters it. It is estimated that 97% of scientists believe that evolution theory of evolution is true. We have explanations of what happened. It is a shame that some politicians in the government do not believe in it and want to remove it from the school syllabus. After learning about such irrefutable evidence, no sensible person will call evolution wrong.

The evolution of primates is the last part of our story. Research from 2021 found that the ancestors of all primates must have been alive 65.9 million years ago, co-existing with the dinosaurs. The evolution of primates was a big branch among mammals. We see gorillas, chimpanzees, monkeys, and humans evolve after this.

Lastly, I am reminded of a dialogue from Shaunak Sen’s documentary, ‘All That Breathes.’ It was said that life is a relationship. We are a community of air. Whatever breathes should not be discriminated against. This quote may sound spiritual, but if you think about it from the perspective of evolutionary history, it is a scientific statement too. All the species that exist today, such as trees, plants, and animals, exist in an equilibrium. An equilibrium where everyone fits harmoniously. Every species has its place in the ecosystem. Everyone is important in this ecosystem, whether a blood-sucking organism like a mosquito, a shark, or even a scavenger like a hyena. This is all about Theory of Evolution.