Theory of Evolution

Is evolution merely a theory or a fact? Where were our ancestors from? Hello friends! Approximately 4 billion years ago, life began on Earth. After billions of years of evolution, numerous species of plants and animals evolved. All these trees, plants, animals and creatures that you see today, all of them exist due to evolution. One of these species is Homo Sapiens, that is, humans. But the question arises, if humans came from apes, then why do apes still exist? Why didn't all these monkeys, chimpanzees and gorillas evolve into humans? Such questions are often asked by people. Some people deny evolution. They say it's a lie. How true is this evolution theory? Is it merely a theory or a fact? And how did these different types of animals evolve? Let's find out in this article. Let's begin with clearing the biggest misconception. Evolution theory doesn't claim that monkeys became humans. Instead, it claims that all chimpanzees, gorillas, monkeys and humans have the same ancestor. And that ancestor is not alive today. If you want to visualize evolution, imagine a tree. A tree starts with just one stem. Then it grows branches. Then it grows smaller branches. If it keeps growing such, you see the tips of the tree. Those endpoints are all the living creatures that exist today. But one question that will still linger in your mind is, why did some of our ancestors evolve into humans and some into chimpanzees and some monkeys? Why? You will get the answer later in this article. In the year 1859, Charles Darwin wrote the historic book ‘On the Origin of Species’. In this book, he talked about the theory of natural selection. Now, when you hear the term ‘theory of natural selection’, you might feel that it is a mystical thing. There must be some complicated inner engineering in all living beings. But, no. It’s actually very simple. Whenever there is reproduction, whether it is in humans, animals, trees or plants, genes pass on from one generation to another. Our genes pass on to our children. But the genes pass on with certain mutations. There are slight changes in the genes. You can see some variations. And these variations are often inherited by future generations. For example, if you have brown eyes and your children have green eyes, it means that a mutation has occurred in their genes. The genes that decide the colour of the eyes mutated. It is possible that the next generation of their children will also have green eyes. Often, these variations are beneficial and harmful, depending on the environment. Some survive and some die out. This process is called natural selection. For example, let's say a frog, which is brown in colour, lives in a jungle. It has 5 children. 4 of the 5 are brown in colour and the one is green. The green frog can disguise itself well and can camouflage itself among the green trees. This gives it an advantage. One day, a predator comes and eats the brown frogs because they are easily visible. But this green frog is not spotted, it is safe and so its descendants are also green in colour. In a similar way, broadly speaking, the theory of natural selection works. Here, a term is used, ‘Survival Of The Fittest.’ Many motivational speakers misuse this term by saying that only physically fit people will be able to survive. People imagine that only those who have big biceps, triceps, and six-pack abs, will be able to survive according to the Theory Of Natural Selection. But this statement is wrong. Fit doesn't mean the biggest, the most powerful person. According to Charles Darwin, fit means the one who fits best in the environment around him. Here, the environment doesn't mean just the climate and temperature around you. It also includes the plants and animals around you. Who fits the situation the best? So, whether you are fit or not, can change with time. During the era of dinosaurs, due to natural selection, some evolved to be huge. Because a bigger size could easily protect them from their predators. But on the other hand, when there was a lack of food, being fit meant downsizing. So that the food requirement could be reduced as well. So, some evolved to be smaller in size. Similarly, some animals evolved to have more hair on their body so that they could get more insulation in the cold. Like polar bears. With their thick fur, it is easier to stay warm in cold weather. But on the other hand, some animals like humans evolved to have less body hair. So that it's easier to regulate their body temperature in summer. Now that you have understood the basics, let's understand how evolution happened. On the tree of evolution, if you go back in time you will find common ancestors with every species. Humans and monkeys have a common ancestor. Humans and cows and buffaloes have a common ancestor. All animals and trees and plants have a common ancestor. If we go back in time, it began approximately 4 billion years ago. The earth was vastly different at that time. There were no continents on Earth. Earth was covered with only water. And this water is where life began. What was the first organism? Scientists have given a very simple name to this first organism. They have called it the First Universal Common Ancestor. In short, it became FUCA. At that time, there were no genes, no DNA. There were just some free-floating nucleotides which assembled into an RNA. This RNA made a molecule called PTC and self-organised to form FUCA. The first ancestor for all of us was not even a cell. Today, we call cells the building blocks of life. But since FUCA was not even a cell, was it even a living thing? Was it living or non-living? It's difficult to imagine. But imagine a virus. A virus is neither called living nor non-living. A virus cannot grow or reproduce on its own unless it is in a host's body. Imagine something like this. I won't go into the technical details here because that would need a separate article. How, in the beginning, there were only a few elements which became nucleotides and then RNAs. If you want me to make a separate article on this, let me know in the comments. But for now, let's move ahead. 3.8 billion years ago, FUCA evolved into a unicellular organism. We call it LUCA, Last Universal Common Ancestor. All the living things on earth, trees, plants, animals, bacteria, and fungi, all of us have a common ancestor, LUCA. Scientists believe that it must have been a prokaryotic microbe with a cell membrane. You must've studied the difference between prokaryotes and eukaryotes in school. Eukaryotes have a proper nucleus in the cell. Whereas, Prokaryotes don't have a proper nucleus. Scientists have estimated that there were about 355 genes in LUCA. These 355 genes are found in every organism living on Earth to date. But this is a very new discovery. Scientists discovered this in July 2016. William Martin of the University of Dusseldorf made this discovery. Four months before this discovery, scientists created the smallest synthetic cell that can survive and reproduce on its own in a laboratory. There are 473 genes in the synthetic cell. But in LUCA, there were 355, fewer than in the synthetic cell. That's why LUCA is classified as half-alive. It wasn't properly living. Scientists believe that the viruses we see today, must have started evolving either before LUCA or the viruses must have started co-evolving with LUCA. Because from the very beginning, viruses have played a crucial role in evolution. Even though the COVID-19 virus was the black sheep of the virus family, but, for our survival today, everything needs some virus or other. With LUCA, we saw it reproducing through cell division. And evolution took place after millions of years when LUCA branched out into two. Bacteria and Archaea. These two microorganisms are very similar to each other. They differ slightly in terms of the cell wall and plasma membrane. Many billions of years later, a very special type of bacteria emerged due to evolution. Cyanobacteria. This was the first bacteria to be able to do photosynthesis. Using sunlight to generate energy. Water was used as fuel and the end product was oxygen. When a lot of cyanobacteria in the ocean used photosynthesis, a large amount of oxygen was released into the air. This event is called the Great Oxygenation Event. This led to high levels of oxygen in the atmosphere. This event took place 2.2 billion years ago. But evolution had to step in here to make the DNA stronger and more protected. This led to the formation of the nucleus in the cell. DNA was kept safe inside the cell so that it could be protected. Secondly, after millions of years, we can see evolution outside the nucleus, in the cytoplasm. Some types of cyanobacteria turn into chloroplasts. This is why all plants and trees are able to photosynthesise today. This was the birth of the plant kingdom. On the other hand, since there was an abundance of oxygen in the atmosphere, an ancient bacteria decided to use this available oxygen. To use oxygen to generate energy. This was the beginning of Aerobic Respiration. This bacteria evolved further inside another Archaea to form Mitochondria, which is now known as the powerhouse of a cell. An important element in all eukaryotes. Later on, these eukaryotes split into three sub-branches. The animal kingdom, fungi kingdom and algae kingdom. The Algae Kingdom is also called Protista. Here you can visualize the Tree of Life being born. Initially, there are three branches, bacteria, eukarya and archaea. And then eukarya branched out 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. By now you must be thinking about when will we get to monkeys evolving into humans. Here we are still talking about bacteria and microorganisms. Some people are ashamed that humans are related to monkeys and here we are talking about bacteria. *How insulting!* But this is the truth, friends. In each of our bodies. Only 43% of the cells in our body are human cells. The rest are bacteria, viruses, fungi, and RKI cells. If we go back to the story, about 900 million years ago multicellular life was born. Why? Because of evolution. It was easier to survive if the cells were in a group. Instead of being unicellular and alone, multicellular organisms had increased chances of survival. That is why we see multicellular organisms. About 555 million years ago, we see a common ancestor of all animals. The Ikaria Wariootia. It was smaller than a grain of rice. It was a bilateral worm which had a front and a back end. Bilateral refers to the symmetry. The organism would be vertically or horizontally symmetric. It means that all organisms would have a right side and a left side. And both sides are similar to each other. There are very few exceptions to this. Such as a starfish, that has radial symmetry instead of bilateral symmetry. In fact, all animals are bilateral. Be it a human, a pig, a spider or a butterfly. So, the scientists found these fossils in South Australia and when the fossils were carbon-dated, they were found to be from a creature that lived 555 million years ago. It was also a bilateral creature. It is considered to be the oldest organism ever discovered. This is why it is known as the ancestor of all animals. Then the vertebrates, or the spine, started to develop. All fishes, reptiles, birds and mammals are called vertebrates because they have a spine. The first spine was developed 480 million years ago. It was a fish called Arandaspis. After this, organisms started evolving to have four legs. The animals that have four legs are called tetrapods. And this development happened in water. We haven't come up on land in this story yet. 375 million years ago, this fish lived, which is called Eusthenopteron. It is a 6 feet long fish, with a very strong jaw and sharp teeth. It is said to be the connection between all the fish and land vertebrates. Perhaps one day, the fish said, fear is the way to victory, and it moved from water to the ground. I'm kidding, evolution does not work like that. Look at this animal. The Tiktaalik Roseae discovered in 2004. Its big fore fins were able to support it to be able to live on the ground. Realistically, this animal must have been living in a shallow ocean. Many times, due to climate changes, the ocean receded and it was forced to stay on land and it was able to survive there. Its skull was like a crocodile so it could bite and eat. But that doesn't mean that all the organisms moved from water to the ground. Evolution never has a linear progression. It doesn't move in one direction. Evolution can happen in all directions. This fish was a relative of this Tiktalik. Qikiqtania Wakei. It is believed that it came to the ground for a while, but couldn't adapt to the conditions, and went back to the sea. Similarly, some organisms came to the ground but went back to the sea to evolve. Some good examples of this are whales and dolphins. Whales and dolphins are mammals. They are more closely related to humans than fish. Unlike fish, they can't breathe underwater. They have to come up to the surface to breathe. This means that dolphins and humans must’ve had a common ancestor who lived on the ground. Some of the descendants of those ancestors stayed on the ground while some went back to the sea. If we move forward in the story, 368 million years ago, amphibians began evolving. Amphibians are animals like frogs and salamanders, which can live in water as well as on land. Then began the evolution of reptiles. Snakes, turtles, alligators, crocodiles, lizards. Dinosaurs later evolved from this branch. Dinosaurs started coming around 230 million years ago. And if you want to know the story of their evolution in detail, I discussed it in the article on dinosaurs. When did dinosaurs start evolving first and when did they die out? I will put the link to it in the description below in case you haven't seen the article. Moving forward, 225 million years ago, we see this 20 cm long animal that looks like a mouse. It is named Brasilodon Quadrangularis. It is now considered the oldest mammal in the world. It was discovered last year. Before this, scientists believed that the oldest mammal in the world was Morganucodon, which looked something like this. It existed 205 million years ago. The interesting thing is that it used to lay eggs. Mammals, as we all know, are such animals who are fed their mother's milk. Humans, monkeys, dogs, cats, tigers, lions, all these are mammals. Normally, mammals do not lay eggs. But exceptionally, the mammals that do lay eggs are called monotremes. Today, 5 species of monotremes are alive. One of them is the platypus. Platypus fossils have been found from as early as 120 million years ago. Those fossils were not much different from today's platypus. There were only a few changes. That is why platypus is considered one of the most primitive animals to be still alive. Apart from monotremes, there are two more branches in mammals. The placentals and the marsupials. Placental mammals are animals in which babies develop in the uterus of their mother, such as humans. But marsupials have a pouch for their babies to develop in, such as kangaroos and koalas. So basically, there are three different ways to nurture a child across these three branches of mammals. One is by laying eggs. The second is nurturing it in the womb. And the third is nurturing it in a pouch. They are all grouped together in the category of mammals because the babies drink their mother’s milk. Monotremes diverged from the rest of mammals 166 million years ago. Then, 125 million years ago, marsupials and placental mammals evolved in different directions. Till 40 million years ago, the continents of South America, Antarctica and Australia were connected. So when marsupials evolved, they spread over these 3 continents. At that time, there was no ice in Antarctica. Antarctica had a forest too. Today, when these continents have separated, we see marsupials only on these 3 continents. But most of the marsupials are found in Australia. In South America, they couldn't compete with the other mammals to fit in. But in Australia, they did not face competition from other mammals, that's why we see animals like kangaroos and koalas only in Australia. The oldest fossil of placental mammals was found in northeast China, dated to be from 125 million years ago. This animal's name is Eomaia. However, in a 2013 study, scientists countered this by saying that this animal did not have all the features that we see in the rest of the placental mammals today. Maureen O'Leary and her co-researchers countered this and said that the first placental mammal was actually found only 65 million years ago. And that animal looked like this. It looked even more like a rat. Now we are coming to the most interesting part of the timeline because, at this time, the dinosaurs had already been extinct. The asteroid had killed all the dinosaurs. But this meant that mammals had a chance to dominate. There were many empty spots in Earth's ecosystem where mammals could fit in. A study published in the Science Journal has shown that the boom in placental mammals began only after the dinosaurs went extinct. If this hadn't happened, we would never have seen diversity in placental mammals. Humans would never have existed. 40 million years ago, the Indian continental plate collided with Asia, which formed the Himalayan mountains. At the same time, placental mammals split into different branches. One such branch is that of the Ungulate, the mammals with hooves. Cows, buffaloes, pigs, goats, camels, deer, and hippopotamus, all belong to this category. This branch was later divided into even-toed and odd-toed ungulates. The animals with an even number of toes and the animals with an odd number of toes. Some of the odd-toed ungulates are donkeys, horses, zebras and rhinoceros. The rest of the examples were even-toed ungulates. Apart from these, another branch was formed of the Carnivora Order. Carnivorous placental mammals. Dogs, cats, lions, tigers, and hyenas all of them belong to this category. Interestingly, whales and dolphins are classified as Cetaceans and their closest ancestry is with Ungulates. You heard it right. It means that whales and dolphins are most closely related to cows and buffaloes. Then there was the category of Afrotheria. It includes elephants and this small animal called Hyrax. Evolution never ceases to surprise you. How can a big animal like an elephant and this small animal belong to the same category? How can they have the same ancestor? This is possible because evolution does not happen in a linear fashion. It happens in every direction wherever it can fit. What are the reasons behind evolution? There are 4 main reasons. These 4 reasons are known as the Four Forces Of Evolution. I have already told you about two of the four. One is the genetic mutation. The mistakes while replicating the DNA causes mutations in the genes by chance during reproduction. It can be due to external factors as well. Such as ultraviolet light causing your skin cells to mutate and you get skin cancer. The second is natural selection. The traits of the genes that naturally fit the ecosystem the best evolution continues from there. But what are the third and fourth reasons? Let's talk about them now. The third reason is the Genetic Drifts. Basically, think of it as a big explosion in the environment, which changes everything. A big destructive event. Let's say there is a specific species of animal which is found on a specific island. And a volcano erupts on that island. Everything is destroyed. That animal will also be destroyed. But if a subspecies of that animal was present on a nearby island, then after a volcanic disaster, that subspecies will get a chance to continue flourishing. And in the future, that subspecies will be found everywhere. This type of event is called the bottleneck effect type of Genetic Drift. This happened in America hundreds of years ago. North American Bison were found everywhere in America. But humans hunted it to extinction. But a subspecies of it, called Plains Bison, survived in a national park in America. 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, which led to genetic drift. And all the bison in America today belong to this subspecies of Plains Bison. These bison came from merely about 100 individual ancestors. The 100 bison that survived in Yellowstone National Park by chance. Another type of genetic drift can be the founder effect. When a small population of an animal gets isolated and then goes to a place and reproduces. A good example of this can be seen among humans too. The Amish people. Amish people are a small community living in America and Canada. Their population is around 250,000 people. Their ancestors came from Germany and Switzerland around 200 years ago. Interestingly, only around 200 people came to America and Canada. But this community was so conservative that they never married any outsiders. They kept intermarrying within themselves. The result of this is that for the population of these 250,000 Amish people, their ancestors were among those 200 emigrants. To racists, this might seem like an excellent thing. Them getting married within themselves. But according to Charles Darwin, reducing genetic diversity is not a good thing. One of his 200 original founders was a person with a recessive gene which causes the Ellis-van Creveld syndrome. It's a disease that makes your hands and feet smaller and you have more fingers. Since they kept intermarrying among themselves, this recessive gene kept being passed on. And due to evolution, today, this disease is found proportionately more among Amish people than in any other species globally. So, from the perspective of evolution, genetic diversity is always better. To see intermixing in different types of genes. Now, let's come to the fourth reason, which is gene flow. This is similar to genetic drift, but here a population migrates towards another and there’s mixing between the two. An example of this is the insecticide resistance gene found in African malaria mosquitoes. This resistance gene was found in some other species of mosquito. But when the population of that mosquito came and interacted with these African mosquitoes, they passed on this insecticide resistance. Here, you might be wondering about the timeline of evolution. How fast or slow is evolution? There is no concrete answer to this. It depends on the species. Evolution can take millions of years, as we saw in the case of mammals. But on the other hand, it can take a year or two. A good example of this is the coronavirus. We have seen so many mutations in the SARS-CoV-2 virus since the COVID-19 pandemic started. The Delta variant, the Omicron variant. What else was it if not evolution? That's why it's surprising that some people still don't believe in evolution. Evolution is not just a theory, it is a fact. When we use the word theory, it means a scientific theory. A scientific theory 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. They are known as theories, but they are facts. In this article, you understand the irrefutable evidence proving evolution. But there is no evidence to counter this. To prove that evolution is not true. It is estimated that 97% of scientists believe that evolution is the truth. We have the explanations of what happened. It is a shame that there are some politicians in our government who don't 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. And so we come to the last part of our story. The evolution of primates. Research from 2021 found that the ancestor 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. It was only after this that we get to see gorillas, chimpanzees, monkeys and humans evolve. What happened next? When and how did actually humans evolve? Let’s discuss this in a future article. That deserves a separate article of its own. Finally, it bears mentioning, I am reminded of a dialogue from Shaunak Sen’s documentary, ‘All That Breathes’. In it, it was said that life is a relationship, we are a community of air. Whatever breaths 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, trees, plants, animals, all of them exist in an equilibrium. An equilibrium where everyone fits harmoniously. Every species has its place in the ecosystem. Whether it is a blood-sucking organism like a mosquito, a shark or even a scavenger like a hyena, everyone is important in this ecosystem