Free Biology NEET Video Lectures for Evolution

00:00:44 Dear students, I hope you’re enjoying the IIT Pal Biology series. Now, quickly, I want to sum up some really important points that have been taught to you, especially from an application perspective, to help you fully understand the concept. The first thing I’ll cover is Mendel’s principles of inheritance. I want to mention that when Mendel was working on genetics, there were no computers—every calculation was done by hand. So, it’s not easy for any of us today to truly appreciate what an incredible discovery that was.

00:01:27 Predicting what kind of flower color or plant type you can get, and how many of those particular colors you might get starting from one specific color, without actually knowing the molecular basis of the gene. So, the principles of heredity that you learn have several applications. One of the most interesting is figuring out how living things are related. Let me try to give you an example from real life. Say you have a friend, and let’s just call him Rahul. Let’s say Rahul...

00:02:07 He has a blood type O. Now, all of you know that blood types fall under A, B, AB, or O. That's one way to categorize them. Another way is whether the blood type is Rh positive or negative. So normally, a blood type has two traits that play a role. The first trait is whether it's A, B, AB, or O. The second trait is whether it’s plus or minus. So, let's just look at this first trait independently. Let's say Rahul has blood type O. Let's say Rahul's mother has blood type A. And let's also say Rahul's father has blood type B.

00:03:09 Now, if the fathers of both the mother and father—that is, Rahul’s grandfathers—were both AB, can you tell me what blood types the grandmothers can be? And can you tell me what blood types the grandmothers cannot be? So, you can actually figure out both problems by understanding the family pedigree in terms of blood types. Let’s try to answer the question, because it’s easier to start with: what blood types can Rahul’s grandmothers NOT have? How do you solve this? Alright.

00:04:17 Alright, let’s say blood type A is going to show up if you have an I with a superscript A. This is the dominant trait for A, so you'll get blood type A. If there’s a recessive trait, you can write it as a small i. So, any dominant trait is written as a capital I. If it’s A, we write I with a superscript A; if it’s B, we write I with a superscript B. If it’s a recessive state, we write a small i. Now in these two cases, the blood type would be A; in these two cases, the blood type would be B. Similarly, if you have two dominant alleles, I and I or I and B...

00:05:17 The blood type would be AB. So, to have blood type O, Rahul must have both recessive alleles. That means we can write for Rahul like this. Now, since Rahul has two eyes which are both recessive, that means one eye must have come randomly from the father and one from the mother. So let's say this one came from mom, and this one came from dad. Therefore, if the mother is A, then Rahul’s mother must be IAI because it can’t be this. Otherwise, Rahul would have had one dominant and one recessive phenotype. On the other hand, the father has blood type B, so the father must be this. Now, let’s go back.

00:06:14 To mothers, grandmothers, father's side comes first, then father's father first. Now, if the mother's father had blood type AB, and the mother's father was AB, that means the mother's father had this, and the mother got the A from the father. Similarly, the father's father must also be AB since the father has this; it must have come from there. Therefore, Rahul's grandmother from the mother's side must have an I, and Rahul's grandmother from the father's side must have an I. Is that right? So, if the grandmothers must have one recessive gene, what blood type can't they have? Well, where both of them are dominant. That means Rahul's grandmother...

00:07:38 Mothers can't have this blood type. So what you can do is definitely rule out whether Rahul’s grandmothers had the AB blood group or not. You can say with a lot of confidence that they did not have the AB blood group. This is an important application, and as you can see, you’ll find uses for this not just in forensics but also when you need to locate family members or actually look at how organisms are related based on traits like blood type. You can use these principles to figure that out.

00:08:24 Of heredity. So this is one important application that you must keep in mind. The next concept, which is considered one of the toughest based on feedback from students in 11th and 12th grades, is photosynthesis. It’s assumed that this is just a memorization-based topic that you have to learn. That’s not true. The way you’ve been taught very well in the IIT pilot biology lectures by your professor, you must realize that the key to understanding the concept of photosynthesis is as follows.

00:09:07 The electron— as long as you keep track of the electron moving from one spot to another in the photosystems, you’ll be fine. That’s the main idea you need to get. The important thing to think about before following the electron is: where is the electron coming from? So, like you were told, in photosystems, photons hit, and that starts the energy transfer process. The wavelength of a photon, let’s say it’s lambda, is connected to the energy carried by that photon.

00:09:50 The de Broglie equation is e = HC / lambda. So, the main concept to keep in mind is following the electron. You also have to remember that in a photo system, if the wavelength of light hitting it is shorter, it provides higher energy, and if the wavelength is longer, it provides lower energy. As long as you keep these analytical concepts in mind, you'll be comfortable understanding photosynthesis conceptually without needing to memorize. Finally, you will now start learning a very...

00:10:36 The fascinating part of biology is called evolution, and we'll cover it in the next few lectures. There are a couple of things I want you to really understand when you're learning about evolution. First, make sure you get that evolution doesn’t happen because someone wants it to. It just happens by chance. For example, if you want to become resistant to fire right now by walking through it, it’s not going to happen because your skin will burn. We’re all made of the same stuff. However, in some groups of...

00:11:20 If there’s one organism that happens to develop scales by chance, and then there’s a big fire, all the other organisms will die. Only the one with scales that can resist heat will survive. Now, when this organism survives, it will multiply, so the species or group of organisms you see left are only the ones with scales. This is random evolution, right? This is how evolution actually happens. There’s no knowing where it will go. So, in the end, that’s how I understand the concept of evolution.

00:11:57 I want you to think about this. There are two groups of people and humans that you see. The first group has webbed feet. This is a trait where instead of having feet with five toes, you actually have feet that look like this. There is one tribe in the world that looks like this. So that means the feet of these humans actually look like this rather than like this. The second group of people are those who can walk on fire. You must have seen, we have lots of places in India where there are people who can sleep on beds of nails. They can walk on fire too.

00:12:48 Coal and things like that. So, I want you to think about which would be an example of evolution? If you join this group, do you think an organism would be born with the ability to work with fire? Or do you think an organism would be born to work on web feed? I hope you'll be able to answer such an analytical question based on the evolution lectures you'll get in the upcoming series. Thank you. Hello friends, welcome back to the IIT Pal series of Biology. This is your learning partner, Rikisha Bhaumik, PGT.

00:13:34 Biology from Kendriya Vidyalaya Sector 2, RK Puram. Hey friends, life is always changing, and so is the Earth along with all the living things on it. Did you know there’s a huge variety of life out there, with so many species unknown to us? Do you think the living things we see today have stayed the same since life began on Earth? No, like I’ve already told you, life is dynamic. The word dynamic means always changing. The plants and animals we see on Earth have been changing over millions of years.

00:14:25 I'm here to help you with this change. As you might have guessed, today in this session we'll be covering the topic of Evolution from your Class 12 NCERT Biology. So, what will you learn in this session? You'll learn about the process of evolution, the beginning of the universe, how life originated, various theories about the origin of life, the theories proposed for the origin of life, the theory of use and disuse of organs, and then Charles Darwin's theory of natural selection. So, before we start...

00:15:09 Let me give you a flowchart showing the steps starting from the origin point of perspective. As you can see, here’s how the universe began. Let me tell you one thing right off the bat: even the universe had a beginning. Before the universe, there was nothing. Was there space? Just an infinitely large, empty void. The universe had a definite beginning, about 20 billion years ago. There might be some variations, maybe between 15 to 20 billion years ago. So, the universe started around 20 billion years ago. Then the next steps we arrow to...

00:16:00 It was about the origin of the Earth, the galaxy, the solar system, and the Earth itself, which happened around 4.5 billion years ago. The earliest life-like structures and the first organic molecules were formed about 4 billion years ago. Then, slowly, atmospheric oxygen started building up in the Earth's environment, and this happened around 2 billion years ago. After that, the earliest eukaryotic cells appeared about 1.5 billion years ago. So, you can see this is the sequence of events that happened after the universe.

00:16:52 The universe was formed. The universe began it all. Let’s go over the origin of the universe again—about 20 billion years ago. You have to go way back on the timeline and imagine how evolution took place. The universe started 20 billion years ago. Then, after the universe came into being, there was nothing for a long time. The Earth formed about 4.5 billion years ago. The earliest life-like molecules, which could give rise to life, appeared around 4 billion years ago. Atmospheric oxygen started to build up about 2 billion years ago.

00:17:33 The first eukaryotic cells were found about 1.5 billion years ago. So, let’s start by looking at how the universe began, how the Earth came to be, and what processes were involved. Like I said, the universe started around 15 to 20 billion years ago. The most likely theory about how the universe began is the Big Bang theory, which tries to explain the origin of everything. The Big Bang theory is the most accepted one because, even though there have been many theories, this one makes the most sense.

00:18:15 The most logical and straightforward theory that helps us make sense of things is the Big Bang theory. Obviously, since there was nothing around back then, we don’t have any experimental proof. But just so you know, there are some experiments you’ve probably heard about, like the Large Hadron Collider, which is being used to check if the Big Bang theory is the right explanation for how the universe began. So, what exactly is this Big Bang theory? According to it, there was a single explosion. A single explosion.

00:18:55 Which was unimaginable in physical terms. This singular term implies that there was a singularity. This singularity is the infinitely dense condensation of whatever was present in that space, and when it exploded, there was a kind of formation—and this formation was the formation of the universe. We can't describe it in terms of matter or energy because the concepts of matter and energy only came about after the universe was formed. Before that, there was no matter, no energy. So what happened after the Big Bang? After the Big Bang, the universe...

00:19:36 It started expanding, and we can still see that expansion even now. Right after the huge explosion, the universe began to expand and the temperature dropped. Because of that, certain gases formed, mainly hydrogen and helium. You should know that hydrogen and helium are the building blocks of most stars. In fact, all these stars, including our sun, are made up of hydrogen and helium. This led to the formation of galaxies. These gases clumped together under gravity and formed different galaxies. One of those galaxies was our galaxy, the...

00:20:16 The Milky Way galaxy is where our solar system is located. Our solar system includes the Earth. Earth is the planet we live on and call home. Earth was also formed through this process. This idea is known as the Nebular Hypothesis. There are many theories that explain how Earth came to be, but the most likely and logical one is the Nebular Hypothesis. According to this, hydrogen and helium gases, which were formed earlier, condensed under gravity, and from this process...

00:20:55 Condensation started forming galaxies, and one of those galaxies was the Milky Way. Now that you know how the universe began—the universe started with the Big Bang. Then I told you that gases began to condense. Hydrogen and helium were formed, and galaxies came into being. Earth was created. But do you think the Earth that was formed is the same as the Earth we live on today? Definitely not. The conditions on the early Earth were very different from what we see now. Here, you can see a picture of Earth. It...

00:21:40 It looks green, it looks blue—actually, it’s a mix of different colors. This picture was taken from space. But this wasn’t the real Earth as it actually was. So, what was Earth like? When Earth first formed, it wasn’t habitable at all. Why? What were the conditions that made it unlivable and then eventually livable? Number one, there was no atmosphere like we have today. There was no free oxygen. The environment was reducing because of gases like water vapor, methane, carbon dioxide, and ammonia. Can you imagine living in conditions like that? Can you?

00:22:24 Imagine living under these kinds of conditions? No way, life just can’t survive like that. Plus, ultraviolet rays could easily penetrate the Earth’s surface. We know UV rays are super harmful to us. They’re the sun’s radiation that can cause skin cancer and damage aquatic life and plants. So these UV rays could easily get through to the Earth’s surface. On top of that, the temperature was really high and there were volcanic eruptions, lightning, and electrical discharges. All these conditions were pretty much common back in the early days.

00:23:03 Meaning: It’s impossible for us to think that the Earth could support any kind of life form back then. So, how did life start? The big question is, how did life begin? Well, many people have tried to explain theories about the origin of life. That’s why there are these guessed theories about how life began. Guessed theories are those that don’t have any logical explanation and aren’t backed by any experiments. So, we’ll quickly look at what these theories about the origin of life are. The theory of special creation. This was the...

00:23:46 This was the oldest theory used to explain the origin of life. According to this theory, life and the Earth were created together, and the Earth and the life on it were created intact in just six days. It also says the Earth is only about 4000 years old. All the life forms we see today were also present back then. The next theory is the theory of panspermia. This theory says that certain living spores were present in space, and these spores existed in space and on other planets too.

00:24:27 Accidentally, it came to Earth, found a suitable environment, and that's how life started here. But again, there's no solid evidence for this. Then, there was the theory of spontaneous generation and abiogenesis. According to this theory, life gradually arose from non-living matter. I repeat, this theory is also known as the theory of abiogenesis. Abiogenesis means the origin of life from non-living matter. Why did it come into existence in the first place? It just came into existence.

00:25:08 Because we can see that dead and decayed matter gives rise to life. You can see that whenever there’s some dead and decaying matter, certain maggots and flies tend to show up on it. So people thought that these flies and maggots came from the non-living dead and decaying matter. But that wasn’t the case, and what the real truth was, was proven by Louis Pasteur. Here you can see Louis Pasteur’s experiment. So what did he do? He kept a mixture of sugar and yeast, which he called broth, in a flask. He pulled out the neck of the flask.

00:25:58 He bent the neck into an S shape. He molded the neck into an S-shaped structure. So, this experiment is also popularly known as the Swan Neck Flask experiment. Then what did he do? He boiled the contents until steam rushed out and then cooled it down. The contents of the flask were observed for many days, and he saw that no living organisms could come out from this setup. Then he repeated his experiment, but this time with a modification: the curved neck that was present in his earlier experiment was broken off and removed. Then he observed it again for some days, and this time he could...

00:26:42 Observing the growth of certain microbes. So, what can you conclude from this experiment? Yes, you’re right in your thinking. In the first experiment, since the neck was swan-shaped, the microorganisms couldn’t get in, and it was also sterilized. Secondly, in the second experiment, since the neck was cut off, the microbes could easily grow on the dead and decayed matter that was inside the broth. This led to the appearance of spores and the formation of certain maggots and flies. So, that’s the theory, Louis.

00:27:30 Pasteur's theory, also called the theory of biogenesis, says that life can only come from existing life. So, this theory basically disproves the idea of abiogenesis, which is the theory that life can come from non-living stuff, and also goes against spontaneous generation. Before Louis Pasteur's experiment, some other scientists like Francesco Redi and Spallanzani also tried to disprove this idea with similar experiments, but Pasteur's was the most convincing.

00:28:21 The experiment was done by Louis Pasteur. So, I think these theories are pretty clear to you. The conjecture theories we covered—the first one was the theory of special creation, which believes in some super powerful supernatural force under which all life was created on Earth in six days. Then we had the theory of spontaneous generation and the theory of transpermia. Now, we agree on the fact that once life originated, all life forms came from pre-existing life forms. But what about the very first life form? How did it come about?

00:29:01 Originated? Well, we’ve got a theory and a hypothesis for that, and this theory was proposed by Oparin and Haldane. It’s also known as the theory of chemical evolution. This theory explains that life began through chemical evolution. Oparin and Haldane from England suggested that the first form of life might have come from pre-existing non-living organic molecules like RNA, proteins, etc. Oh dear friends, you know very well that there are certain molecules, biomolecules, which are present inside our cells and it is the...

00:29:43 Interaction is basically the movement of these molecules, which gives us a key feature. So, the most logical explanation is that these non-living organic molecules formed first, and from these non-living organic molecules, life might have first arisen. So, this condition that was present on Earth at that time could support the theory of chemical evolution and the chemical origin of life. This is also described by Haldane as the "hot dilute soup." This suggests that the conditions on primitive Earth were suitable.

00:30:26 For making carbohydrates, fats, amino acids, and other complex organic stuff. These carbohydrates, fats, and amino acids are the building blocks of the biomolecules found in our cells. And this making process probably happened in the sea. We know the first life appeared in water. Simple organic molecules then joined together to form complex organic molecules. So, to put it simply, the first simple biomolecules formed were carbohydrates, RNA, and proteins because...

00:31:05 Of the sequence of chemical reactions that took place due to the conditions present on primitive Earth. Then, from these biomolecules, simple molecules could come together and further polymerize and condense to form complex organic molecules. Now, this is the experimental evidence for the chemical theory of evolution. So, this hypothesis by Oparin and Haldane appears quite logical in explaining the sequence of events that might have happened on primitive Earth. And as we know, the Earth was very different back then.

00:31:49 From what we know today, the conditions were pretty much right for the chemical evolution of life to happen. This was backed up by an experiment done by Miller and Urey. In 1953, Stanley Miller and Harold Urey recreated conditions similar to those on early Earth in a lab. Check out this figure—inside it, you can see the setup with different parts, including a conical flask holding all the key ingredients that were present on primitive Earth. The gases they used were methane, ammonia, and water vapor.

00:32:35 Hydrogen and the setup were arranged to condense the water vapor so water could form. They used a vacuum pump to collect certain substances, and electrodes were there for the electrical discharges. So when they did this experiment, they recreated conditions similar to early Earth on a small, lab scale, providing electrical discharges and maintaining a high temperature. They were actually able to observe the formation of amino acids. You probably know very well that amino acids are the building blocks...

00:33:15 Building blocks of proteins. So, this theory seemed like a possible way to explain how life began. The origin of life is supported by the theory of chemical evolution, which suggests that the first life forms could have come about because of chemical evolution. Similar experiments were later done by many scientists, and they were also able to create other types of molecules like sugars, nitrogenous bases, pigments, and fats. So, with this understanding, we’ll move on to the next topic, which is the origin of cellular forms. So, we’re making progress.

00:34:00 From right at the very beginning of the universe, to the formation of Earth, then the conditions on the early Earth, and how life actually started in the first place—it was those primitive conditions that led to a kind of chemical reaction, which then caused simpler biomolecules to form. Those simpler biomolecules could then come together and combine to make more complex biomolecules. But what about the very first cell? We're still basically just focusing on how biomolecules formed. How was the cell itself created—the cell that’s the basic unit of life?

00:34:40 Life is the basic structural and functional unit of living things. So, to understand cellular forms and their origins, we need to know some key terms: coacervates. Coacervates are large colloidal particles. These are the names given to big colloidal particles formed because organic macromolecules tend to clump together. So, what are coacervates? Coacervates are basically clusters formed by the aggregation of organic macromolecules. These coacervates formed once biomolecules came into existence.

00:35:21 Because of their tendency to clump together, they formed coacervates. Then Sidney Fox was the scientist who could make proteinoids. Proteinoids were like primitive protein structures, and Sidney Fox also noticed that these proteinoids could arrange themselves into membrane-bound spheres that looked like cells. They could also undergo fission and budding, kind of like prokaryotes. So, we see how macromolecules were formed, then these macromolecules grouped together to form coacervates, and then they formed membrane-bound spheres.

00:36:05 Which was known as microsphere, the first membrane-bound cell formed because of the spontaneous assembly of phospholipid molecules, which were created through the process of chemical evolution. So, this first membrane-bound cell that formed was a rare event in the course of evolution. The formation of a membrane was, I want to emphasize, the real starting point of life on Earth when cells first came into existence. So, the first cellular form originated...

00:36:49 About 2 billion years ago, it was probably a single cell, and the environment was water. The first cell formed in water. So, to sum up what we've studied so far, what can you conclude about the origin and evolution of life on Earth? One thing we're very clear about from this discussion is that the first form of life that arose came from non-living molecules. These molecules are biomolecules, and this idea is called the theory of chemical evolution. But after this process of chemical evolution was complete...

00:37:32 Life came from other life forms. Since then, no chemical evolution has happened because Earth’s conditions changed gradually. The atmosphere went from being reducing to oxidizing because of these coacervates and microspheres. Oxygen started becoming abundant in the atmosphere. The ozone layer began to form, and many changes took place. The temperature dropped. Water was present on Earth. Water vapor, which could easily evaporate due to the high temperature, then condensed back as water. This cycle kept going on for a long time.

00:38:13 This led to the formation of water and a drop in temperature. So, once chemical evolution happened, the conditions on Earth also changed. After the chemical evolution of macromolecules took place, life appeared—the first cell came after that. All life has come from pre-existing life forms. I hope this is clear so far. This theory is known as the theory of biogenesis. So, we can sum it up by saying that the first life that appeared came from non-living matter through chemical evolution, and the life that appeared afterward came from that.

00:38:58 Life comes from pre-existing life forms. This is the theory of biogenesis. So, what exactly is evolution? What is evolution? Is it the origin of the Earth or the origin of the universe? No. The origin of the Earth, the origin of life, is not evolution. But how these life forms have changed over a period of years, over time, is actually biological evolution. So, biological evolution is also known as descent with modification. Descent with modification means that life forms appear generation after generation.

00:39:42 So, in simple terms, with certain changes—and why these changes happen—these changes occur because of how organisms respond to their environment. The environment is constantly changing, and to keep up with it, organisms also change themselves. To be specific, biological evolution means passing traits down with some changes. We can say evolution is the gradual process where an organism changes over time in response to its environment. Evolutionary biology is the...

00:40:26 The study of the history of life forms on Earth. So, this is basically a branch of biology that deals with studying how life forms have changed over time. How life forms evolved over different periods is covered in evolutionary biology. Evolutionary theory explains how life has changed since it first appeared. These theories focus on the changes life has gone through since its origin. To be more specific, in evolution, we mainly look at the changes that have happened since life first began. The changes that have come about in the...

00:41:11 Life forms over time—or over a period of time—fall under this field called biological evolution. And you also know that certain species we see today weren’t around before, which means new species have come into existence. Similarly, some species that were around before aren’t present anymore; they’ve gone extinct. So, this is a process that’s very dynamic. It happens slowly and steadily, but yes, evolution is definitely happening. No matter how life started, it eventually branched out and diversified.

00:41:56 And big props to the biodiversity we see today. So, now moving on to the theories of evolution. Just to recap, earlier we were looking at the theories about the origin of life. Now, we’ll be focusing on the theories of evolution—how life forms have changed and evolved since then. The first theory, the first logical one that came about, was by Jean-Baptiste Lamarck in 1890. This theory is also known as the theory of use and disuse of organs, and the inheritance of acquired characteristics.

00:42:45 I guess you must know the difference between inherited traits and acquired traits. Inherited traits are those passed down from one generation to the next, while acquired traits are the ones we pick up from our environment. So, this theory is about the inheritance of acquired characteristics. It was proposed by Jean-Baptiste Lamarck in 1809. So, what does this theory say? It says that organisms have certain needs, and modifying an old organ or forming a new one happens as a result of those needs.

00:43:27 New need. If an organism has a new need, it can modify its old organs and form new ones to meet that need. This was the idea according to Lamarck. He also said that if an organ is used continuously, it will develop and become more advanced. But on the other hand, if it’s not used at all, the organ will waste away. He also added that these changes that happen during an individual’s life become hereditary, meaning they get passed on to the next generation.

00:44:13 So you’ve got to remember Lamarck’s main ideas: organisms have needs, and these needs lead to changes in their existing organs and the creation of new ones. If an organ is used a lot, it will develop, but if it’s not used at all, it will waste away. The changes that happen during an individual’s life get passed down to the next generation. One of the main reasons Lamarck came up with this idea is because he actually observed a lot of things, and the most famous example supporting his theory is that of the giraffe.

00:44:55 As you can see in this figure, giraffes are supposed to have had shorter necks in earlier times. There was plenty of grass, and they could feed on the grass. They were grazing animals. But over time, when the grasses became scarce, they had to stretch their necks to feed on the leaves of trees. Over a long period, because of the continuous use and stretching of their necks, according to Lamarck, giraffes’ necks got longer. Similar examples were also given by Lamarck, such as reduced eyes in moles.

00:45:41 Because we don’t live in forests anymore, humans have smaller ears compared to other mammals. We don’t need to be alert all the time. For example, rabbits have long ears to catch sounds, but our ears have shrunk in size. Snakes don’t have limbs because they evolved from reptiles, which had limbs, but snakes lost them due to their crawling way of moving. Then there are flightless birds like kiwis and ostriches—they became flightless over time.

00:46:23 They evolved from birds that had wings. But they became flightless because they went to places like New Zealand, where there was no competition and plenty of food. So, they didn’t need to fly from one place to another to find food, which led to their wings shrinking and losing the ability to fly. These are clear examples supporting Lamarck’s theory. But does that sound convincing to you? No, it doesn’t sound convincing to us because, on the other hand, there are many...

00:47:06 Criticism tool Lammks theory. Number one said that new needs give rise to new organs. Ah now new needs give rise to new organs. But we know that man has desired to fly. And if this new need, this desire to fly, was so strong, we would have developed wings by now. But this is not the case with us. The second postulate said that the continuous use of organs makes them highly developed. But many times evolution shows exactly the opposite. For instance, we read, we use eyes for reading the voracious readers do throughout their life. But does this... but does this make their...

00:47:52 Is eyesight more powerful? No. We know that because of aging, eyesight decreases. Vision gets worse, and there’s no improvement or development of our eyesight if we keep using it continuously. Thirdly, the traits an organism acquires in response to the environment are temporary and can’t be inherited. How can acquired traits be inherited? Is that even possible? This idea was strongly rejected by a wise man who did some experiments. He kept cutting off the tails of mice generation after generation for at least 22 times.

00:48:32 Generation after generation, even the 23rd mouse born had a tail as long as its ancestor's. This shows that the characters aren’t inherited directly. The acquired character, like the cutting of the tail, wasn’t passed down from one generation to the next. The tail appears in every generation, even the 23rd. So, Lamarck’s theory was rejected, but it’s still really important because it was the first truly mechanistic theory of evolution. By mechanistic theory of evolution, we mean it was the first theory that tried...

00:49:19 To explain how evolution works, let's start with Lamarck, and now we'll move on to Charles Darwin. You probably already know a lot about Charles Darwin. He was a famous naturalist, scientist, the father of evolution, and a huge inspiration to everyone. He actually followed the scientific method, and here’s how he developed his theory. The interesting thing is, back in 1831, he went on a sea voyage on a ship called the HMS Beagle that went all around the world. During this five-year journey, he made some really interesting observations.

00:50:07 Observations. We'll go over these observations in detail when we cover the topic of UV radiation in our next session. But what he concluded in his speech was really important. He said that all existing life forms share similarities to varying degrees, not just among themselves but also with life forms that existed a million years ago. I repeat, I want to explain this further: all existing life forms share similarities to varying degrees, not only among themselves. All organisms share certain similarities among them.

00:50:50 Not just humans, but also all kinds of organisms and life forms that existed millions of years ago. Charles Darwin is a real inspiration for any science student. I want to mention here that Charles Darwin tried to explore and figure out how evolution works because of the scientific method he followed. It was his amazing observational skills. It was his ability to analyze things, record them, and then come to a logical conclusion that made him so famous. So,

00:51:38 Charles Darwin was also influenced by the work of other scientists. It wasn’t just his own work. He did great work, but he also paid attention to other research that could help his own. For example, Thomas Malthus’s work on population had a big impact on Darwin. What did he say? He said that theoretically, population would grow exponentially if everyone reproduced to the maximum. If there’s no competition, organisms tend to reproduce exponentially, and then the population would also grow exponentially.

00:52:19 Reproduce as much as possible and grow their population, but does that actually happen in real life? No, it doesn’t. Populations don’t grow exponentially in reality. Real populations have limits. That means there’s competition for resources because resources are limited. Since resources are limited, organisms compete with each other. Only some survive and grow, while others that can’t thrive don’t make it. So, Thomas Malthus’s idea about population influenced Darwin, who also talked about the struggle for existence.

00:53:04 Exist in nature. Darwin said that variations which are inheritable and help use resources better will allow those organisms to reproduce more and have more offspring. So, here's how I’d explain it: Darwin said that inheritable variations—that is, traits passed from one generation to the next—that improve how an organism uses resources are beneficial. These beneficial variations help the organism make better use of resources, which in turn helps them reproduce more once they have those traits.

00:53:46 Reproductive ability, reproductive fitness, who will leave more offspring. And they will thrive. Alfred Russel Wallace’s work was also similar to Charles Darwin’s. Alfred Russel Wallace made observations similar to Darwin’s during his voyage to the Malay Archipelago. He was also a naturalist and visited different islands in the Malay Archipelago. He observed similar things as Charles Darwin did. In 1858, he formulated his theory in an essay and highlighted the main points of his essay.

00:54:33 All existing life forms share similarities and have a common ancestor. They’re similar to each other as well as to their ancestors, and they all come from those common ancestors. These ancestors lived at different times in Earth's history. We know that Earth has evolved. Life has evolved since the first life began, and those ancestors lived at different points in time, but they share common ancestors. The geological history of Earth closely matches the biological history.

00:55:15 The history of Earth means the changes that happened on Earth are linked to the changes that happened in living things. So, Alfred Russel Wallace supported Charles Darwin, which helped Darwin present his work confidently. The 19th century was a really remarkable time when all the traditional beliefs and popular theories were strongly challenged by the work of these scientists. Charles Darwin was able to successfully put forward his theory of natural selection. So, what is natural selection? According to Charles Darwin in his book...

00:55:59 The theory of natural selection was given by Charles Darwin. The book he published and shared his ideas in was "The Origin of Species by Natural Selection" in 1859. This became a widely accepted theory and actually became the foundation of modern evolutionary theory. According to this theory, life forms have evolved gradually. Life forms have been slowly and steadily changing over a long period of time. Any population has built-in variation in characteristics. The second point says that the population has built-in variation. There are certain variations in them.

00:56:42 Characteristics and these traits help organisms meet the fitness criteria. Survival of the fittest and natural selection. Certain features and variations that allow an organism to better adapt to changing environmental conditions will increase its fitness. Fitness here refers to reproductive fitness. If an organism can successfully reproduce, increase its offspring, and grow its population and thrive, then that's natural selection. Natural selection means that nature will...

00:57:20 Select the beneficial aspects. Nature will pick only two characteristics. Only those organisms with better adaptations and features will survive. So, let’s sum up what we’ve covered so far. Today, we learned about the origin of the universe, galaxies, and Earth. The conditions that were present on primitive Earth, theories about the origin of life, how life first began, then the theory of biogenesis, opinions and the held theory of chemical evolution, Miller and Urey’s experiment, and the meaning of biological evolution theories.

00:58:06 About evolution, which was explained by Lamarck and Charles Darwin. So, I think we’ve covered half of the chapter today, and we’ll go over the rest in the next session. The natural selection part, which we didn’t finish, will be discussed in detail next time. But before we finish, I want you to think about a few questions. First, do you think chemical evolution of life is possible under the current conditions on Earth? Can chemical evolution still happen today? Second, do you agree that the rate of...

00:58:57 The appearance of new forms is connected to the life cycle and lifespan of an organism. This means the rate at which new life forms show up depends on their life cycle and lifespan. For example, if an organism has a short lifespan, it will reproduce faster. If it has a long lifespan, it will reproduce more slowly. Is this related to evolution in any way? Then the next question is: does nature select for fitness, meaning traits that are inherited?

00:59:37 Characteristics. Nature selects for fitness. This fitness means the traits that help an organism survive in its environment and reproduce its offspring. Which fitness traits are inherited? These are inherited characteristics. Can you suggest how these traits are passed down? What are the ways these traits get inherited? What leads to the acquisition of traits, which traits are inherited, who is responsible for them, and lastly, I want you to think about this. 01:

00:15 That evolution is evolution—a process and the result of some process. So with these questions, I hope your curiosity has been sparked, and when we meet in the next session, we’ll continue from where we left off. Thank you very much. [Music]