Hello, friends!
Homo Habilis, Homo Erectus and Homo Neanderthals are the names of some species that were the closest ancestors of humans.
What has happened to them? Is any of these species still alive?
After them, how did the evolution of today's humans, i.e. Homo sapiens, happen? And perhaps the biggest question is,
has evolution stopped in humans or are humans still evolving?
Let's get to the bottom of these questions in this article which is the second part of my Theory of Evolution series. In the last article, in part 1, I told you how life was born on Earth. And how different types of animals and life forms developed. In that article, I told you the story till the dinosaurs' extinction. Now let's continue that story and know the history of humans. And in this article, as you listen to the story, I will tell you some arguments of those who say that evolution is not a fact. Come, let's start. Let's start our story with the closest living relatives of humans. The animals that are living today and are closest to humans. The Great Apes.
Chimpanzees, Gorillas, Orangutans, and Bonobos, along with humans, these great apes are part of a scientific category known as the Hominids. All of us Hominids have a lot of similarities. Like none of us have a tail. Or we share the common trait of bipedalism. Walking on two legs. Well, it is the most prominent in humans but the rest of the great apes like Gorillas and Orangutans can walk on two legs. But apart from this, or blood group types are the same. A, B, AB, O, RH positive or negative. The blood group types are the same in all of us hominids. These great apes, although they cannot speak like humans, but they can understand human sign language. They can be trained to understand thousands of signs. Research has found that they like to watch TV too. And when they are tickled, they make sounds like laughing too. These similarities are not a coincidence. This is why humans and chimpanzees share a 99% DNA match. And in the second position are the gorillas. 98% of DNA in humans and gorillas is the same. And our third cousins are our orangutans, with 97% DNA similarity. If we take a step back from this, we come to the category of Hominoids.
In this category, in addition to great apes and humans, we include the lesser apes too. Like 20 species of gibbons. If you don't know gibbons, they look like this
and 96% of their DNA matches with human DNA. In the category of hominoids, no one has a tail and everyone has a trichromatic colour vision. The things we can see with our eyes, all the hominoids can see those. The sight remains the same. Now, one step further back is the category of Anthropoids.
In this, we include monkeys along with apes. There are 130 species of old-world monkeys and 120 species of new-world monkeys which are still alive today. The word Anthropoids comes from the words Anthropos + Oid which means Resembling Humans. If we take a step back,
we come to the Primates category in which we include the Tarsiers and Lemurs too. These two species of animals are called Prosimians which means pre-monkey. Tarsiers are cute little monkeys found in Southeast Asia.
When they cry, their voice goes into the ultrasound category, like a bat's voice. When they jump, they can jump up to 16 feet. But you will never see them during the day, because they are shy and nervous. They are sensitive to daylight On the other hand, lemurs have more than 100 species. But they are found in Madagascar only.
They are the oldest living primate in the world. Every category that I have told you so far, has some similarities. The best way to visualize it is, as I told you in the last article, to imagine a tree. An evolution tree,
with numerous branches. At the endpoint of all these branches are the animals that are still alive today. And as you start walking backwards from these endpoints, you will see that two branches join into one. Then two big branches join into one again. So, at the point here these branches are joined you get to know the common ancestors of the different endpoints. And the endpoints of the branches that are closest to humans, those animals are most closely related to humans. Like in the human branch and the branches of great apes, There is a common point that you can circle and say that it is a category of Hominids.
Then, by including the common point with the gibbons in the circle, you can make a bigger circle and say that it is a category of Hominoids.
Similarly, a bigger circle can be drawn for the category of Anthropoids.
And then a bigger circle for the category of Primates.
The smallest circle has the most common things with humans. And as the circles get bigger and farther, similarities keep decreasing. But all primates have a lot of similarities. Like all primates have Prehensile hands.
That is, we can use our hands to hold things. Our hands are designed in such a way. Apart from humans, other primates have grasping feet as well.
They can hold things even with their feet. It becomes a little difficult for humans. Except for three monkeys, all the other primates have five fingers on their hands and feet. And all primates have a large brain size as a proportion of body size. So they are intelligent. Human brains are thrice the size of chimpanzee brains, our closest living relative. So human intelligence could reach the next level. This is why humans could achieve unprecedented technological progress. All primates live in groups. They display complex social behaviour. And the sense of smell in all primates is not very good. The sense of smell of other mammals is much better than that of primates. Like, if you compare dogs to humans. Now, if we look at this evolution tree again, friends, I have only talked about the endpoints. The animals that are still alive. But, perhaps, the most interesting thing are the middle points of these branches. The animals that are no longer alive. There were many middle points between great apes and humans. If you talk about these branches, you will see many more species that were more closely related to humans.
The closest ancestor of humans, who do not exist anymore. Let's go back in time to talk about them, about 60 million years ago. Scientists believe that this was the time when primates evolved.
In 2012, some fossils were found in Montana, which showed that a creature resembling a mouse existed around 65 million years ago. It is named Purgatorius. It is considered the oldest primate in the world. This animal could climb trees. Well, all primates can climb trees, that is why primates are called Arboreal. The word Arboreal means tree dwellers. Paleontologist Jonathan Block
believes that there must have been some connection between the evolution of primates and plants. Primates were attracted to climb up the trees because of the fruits. Evolution ensued due to which grasping limbs were developed. We were able to hold on to the branches. Flexible rotating shoulder joints were developed. Because of this, we can swing from one branch to another. By 'we', I mean all the primates. The next interesting point in evolution comes about 25 million years ago, when the Hominoids were born, and the tail of some primates disappears. The oldest ancestor of humans who did not have a tail was a primate named Proconsul.
The question here is why did the tail disappear? New York University researcher Bo Xia found that a gene is responsible for the tail. Gene TBXT. Only two years ago, Bo Xia found that there was a mutation in the TBXT gene which caused the tail to disappear in the Hominoids. The possible reason behind this is said to be that the primates started walking on two legs. While tails are useful for hanging on trees, but they become very annoying when walking on two legs. This trait of walking on two legs is called Bipedalism. The first ancestor of humans to see bipedalism was Ardipithecus Ramidus.
They lived about 4.4 million years ago in East Africa. It was the first Hominin that walked on two legs. Now, friends, here comes a category of Hominin I have not talked about it yet.
This circle is even smaller than that for the Hominids. Hominins are categorized as Homo sapiens and other species like humans which are no longer alive. this species that I am talking about could walk on two legs but it did so only sometimes, not always. We found out this by studying the hip bones of Ardipithecus.
When scientists excavated the area, they found the skeletons. They looked at the bone structure and how they differ from humans and concluded that they didn't walk on two legs always.
Because their arms reached their knees.
Then comes the Australopithecus Afarensis species which existed around 3.7 to 3 million years ago. These were properly committed bipeds. They always walked on two legs. This is because the shape of their knees is very similar to ours. In Ethiopia, in 1974, a very popular fossil of Australopithecus was discovered which is now known as Lucy.
The most special thing about this fossil was that a large collect of skeletons were found here, which gave us a lot of information. Lucy has been referenced in a science fiction movie, Lucy, where a girl named Lucy travels through time using her brain. And when she goes back in time, she meets Australopithecus Lucy. Watch the image from this movie.
In comparison to today's humans, Australopithecus' hands were still quite long and strong. The oldest stone tools used by our ancestors were found in Kenya.
Dating them, we found out that they are 3.3 million years old. In 2010, where many fossils of Australopithecus were found, some animal bones were also found, which were 3.4 million years old. The bones clearly showed the marks of the use of stone tools. This tells us that Lucy was already using stone tools. But scientists believe that they did not make the tools themselves, but used sharp stones, which were naturally found. This species was omnivorous, meaning it ate meat as well as fruits and plants. The first species that started using tools was Homo Habilis.
We come to the circle of Homo from Hominin. Homo Habilis were alive from 2.5 million years ago to 1.5 million years ago. Their fossils were found in Tanzania and Kenya.
Their height was quite short. They were only 3 to 4 feet tall. During their time, they faced some food scarcities. So, meat was a major component of their diet. But it is still believed that they were not hunters. Mostly, they killed and ate small animals. Mostly, they were scavengers. The meat that was hunted by a carnivorous animal like if a lion killed a deer, the leftover meat after the lions had eaten, the Homo Habilis ate that. They used stone tools to cut the meat and to scrape off the meat from the bones of the dead animals. We can also find out from the marks found on the bones that they actually used to break the bones and eat the bone marrow inside.
Bone marrow is a very nutritious and energy-dense substance. Because of this, their stomachs became smaller. And because of the extra energy they received, their brain size started to grow. Around this time, another species was alive, the Paranthropus, which mostly ate plants. They were more or less vegetarian, but because of a lack of food, this species became extinct. Then we see an evolution from Homo Habilis to Homo Erectus.
Their time was from 1.9 million years ago to 0.14 million years ago. They are also called Homo Ergaster, which means working man. Some scientists believe that Homo Ergaster were African and Homo Erectus were Asian. Why? Because Homo Erectus was the first species to actually migrate out of Africa. North Africa and the Middle East had a climate of deserts, which was very difficult to cross. But the Homo Erectus species did it and spread to different parts of Asia. The reason behind this is that their physical and mental capabilities were much better than their ancestors. These were our first ancestors who had small hands and long legs. Their body proportions were like ours and they could do long-distance running and jogging. If we talk about their diet, they were fruit gatherers as well as amazing hunters. They used spears with stones at the ends to hunt big animals like elephants and hippopotamuses. They also preserved meat by drying it. And the most amazing thing about them is that they get the credit for the first controlled use of fire. They learned to control fire when it was caught naturally. They used to take fire from there and keep it aflame. But later on, they learned to make fire on their own. How did we find out this? In the Wonder Work Cave of South Africa, traces of purposeful fire are found When scientists did carbon dating, they found that they were from more than 1 million years ago. About 0.5 million years ago, about 500,000 years ago, this species learned to cook meat. Because of eating cooked food, they had a constant supply of meat. They had excess energy in their body, which was used to increase the size of the brain. The size of his brain increased to 900 cubic centimetres. Because of this, his digestive tract also reduced and the teeth became smaller. Scientists believe that they lived in large groups. And that there was social interaction among them. Although there was no fully developed language with which they could communicate, but there was a proto-language. To communicate with each other, they used broken language. And after this, in our story finally enters the Homo Sapiens.
Homo Sapiens means Wise Man, which is the species of humans today. Our species appeared for the first time, 0.3 million years ago, about 300,000 years ago. But some scientists believe that the Homo Sapiens that existed then should be counted as a different species. So, scientists call them Archaic Homo Sapiens and the species that emerged 150,000 years ago are called Modern Homo Sapiens which are similar to the humans of today. Specifically, this date is said to be 160,000 years ago. The most special thing about Homo Sapiens was that its brain size had increased to 1,350 cc. Our ancient ancestors, Hominins had some power of reason. But with the help of such a big brain size, humans could make art for the first time. Evidence of abstract thinking in humans is seen since then. This is the creative thinking that is said to have helped Homo Sapiens to spread all over the world. And today, they are dominating the entire planet. The interesting thing here is that, as I told you in the last article, evolution is never in one direction. Evolution can take place in every possible direction. This means that there is no straight line here, from Homo Habilis to Homo Erectus, from Homo Erectus to Homo Sapiens. There must have been evolution in other branches as well. And this is the reason why we find many other species of Homo, which can be called cousins of Homo sapiens. There are many examples of this
The word Neanderthal basically means a person who came from the Neander Valley of Germany. They were named so because, in 1856, their first fossils were found in this area of Germany. What's special about them is that they lived in the higher latitudes of Europe and Asia, where it was very cold. In comparison to Homo Sapiens, they were a bit shorter in height, their noses were a bit bigger, and their hands and feet, lower legs and lower arms had smaller bones. All these adaptations happened due to evolution because they lived in the cold. Their front teeth were bigger, and their hips and shoulders were wider. The brow ridge above the eyebrows was more prominent. It was also found that they were actually quite intelligent. They used to paint in caves. They used to decorate themselves with feather jewellery. They had social relationships among themselves. They used to show compassion. They had the ability to listen and speak and they used to bury their dead in the ground. But around 40,000 years ago in Europe something happened which is said to be the reason for their extinction. Some stalagmite stones were found in the caves of Romania. When those stones were analyzed, it was found that between 44,000 years ago and 40,000 years ago the climate of Europe had become much colder Neanderthals mostly ate meat and could not survive this climate change. By comparison, Homo Sapiens like us had a very varied diet. They ate not only meat but also fish and plants. They had long trade networks which helped in building up a buffer during famines. Another reason is said to be that Neanderthals had bigger eyes than us. Because in Europe, in winter, the nights are longer, so they were adapted to see more at night. Their visual processing area in their braines was bigger than ours. And because of this, the high-level processing and complex social relationships forming areas were smaller. They could not collaborate with each other like Homo Sapiens. And a final reason is that their overall population was only around 5,000. When two different genomes were studied, after their bones were discovered, it was found that their DNA was almost completely identical to each other. The DNAs of the parents of two different individuals were shared. There was very little gene diversity among them, which was another major factor for their extinction. The most amazing thing is that around 45,000 years ago, Homo Sapiens had actually reached Europe and Western Asia. So, there is an overlap of about 5,000 years, where Homo Sapiens and Homo Neanderthals existed together. At the beginning of the article, I raised a question.
Does any other human species still exist today?
The answer to this is, to some extent, yes, if you acknowledge intermixing. When modern human DNA was analyzed, it was found that there was some interbreeding between Homo Neanderthals and Homo Sapiens. Many people living today, were found to have about 2% Neanderthal DNA. So in a way, some part of the other species of our ancestors still survives. Another thing to note here is that as research progresses, more bones are discovered in excavations. New species of human ancestors are discovered. Like this 2-year-old article.
Paleoanthropologists discovered this new species, which they named Homo Bodonensis. The next question here is,
are humans still evolving? Are we seeing any evolution in Homo sapiens?
The answer is obvious, yes. Evolution is a continuous process that never ends. There is evidence of evolution in Homo sapiens in the last thousands of years.
Anthropologists Nina Jablonski and George Chaplin claim that a major example of evolution is our skin colour. This is also a variation caused by evolution. Thousands of years ago,
people who started living in northern areas far from the equator, their skin colour became lighter and more white. Because in those areas, the sun didn't shine as much. Ultraviolet levels were low.
This is the reason why there is a smooth gradient in human skin colour when you move form the equator to the poles. People who live in sunny areas, have the darkest skin colours, such as in Africa or the tribals in North Sentinel Island. Another recent example of evolution is the ability to digest milk. Lactose tolerance. In Scandinavian countries like Finland and Sweden, lactose tolerance is the highest there. Because dairy farming was the most prevalent there. Even in India, the areas where dairy farming is prevalent lactose tolerance is higher, like in the regions of Haryana and Punjab. As compared to regions of South India and East India, where people cannot digest milk as much. If we talk about the whole world, then in Japan, South Korea and Northeast China, the highest percentage of lactose intolerance is observed. Where people have a problem digesting milk because their stomachs cannot handle it. Their body has not evolved in that way. But on the other hand, those who live in the colder places went through evolution for adapting to the cold weather. Look at the eyes of the Siberians, Asians, and Eskimos. You can see fat padding around their eyeballs.
This is called an Epicanthic Fold. This keeps the eyes protected. When you go out into the snow, there is a lot of glare which can damage the eyes. And there are snowy winds too. This fat padding protects the eyes from these things. Apart from this, there are evolutionary variations in small things as well. For example, in South Korea, women have gained 8-inch height on average in the last century. This is because there was an improvement in their nutrition and women who are taller have fewer complications in childbirth. One thing to remember here is that evolution is a slow incremental process. These changes happen slowly and usually over a period of thousands of years. But despite this, all the humans that are alive today, belong to the same species, the Homo Sapiens. Now, the next time you see this famous photo of human evolution,
you will be able to know what is shown in this photo exactly. Here, only the evolution of Hominins is shown. Our close ancestors. In reality, we can go as far back as we want. You will see common ancestry everywhere. For example, if we go back from the primates, we reach the group of mammals. Every mammal has some similarities. As you know, the milk teeth in humans are replaced. The same thing happens with lions and tigers. Or the big whales, their hearts are like a four-chambered heart of a human. Or look at a baby horse.
It drinks its mother's milk just like a human. So people often start the story of human evolution with primates, but it can also be started with mammals. Or if we go further back, we have Tetrapods. Those animals that have four limbs. Like amphibians like frogs, reptiles like crocodiles, or birds like sparrows. All of them have 4 limbs. In 2010, when scientists completed the genome sequencing of an African Clawed Frog, they found that there are about 1,700 genes that are very similar to human genes, with regard to specific diseases, like cancer, asthma, or heart disease. This is the reason why many scientists experiment on frogs when they want to test some things. But the story can be started before this. With vertebrates. All those animals that have a spine. Zebrafish is one among 34,000 fish species, of the vertebrates living in the water. 73% of DNA of zebrafish and humans matches. In the last few years, Zebrafish has become one of the hottest animals in the field of scientific research. Scientists study zebrafish to understand things like metabolism, genetic birth defects, and cancer. And the results are often applicable to humans. So, they are also used for drug testing. But can we go further back than vertebrates? Of course, we can. Eukaryotes, which include all animals, plants, and fungi. Take the example of yeast. In 1996, yeast was the first eukaryote to have the entire genome sequenced.
What was the result?
The same headlines again. "You and yeast have more in common than you might think." There is a protein called alpha-synuclein. When you see its buildup in a human, the chances of Parkinson's disease are increased. This protein affects yeast too. At least 20% of human genes, which have a role in this disease, their functional equivalents were found in yeast. Edward Marcotte,
a biologist from the University of Texas, conducted a superb experiment. He identifies the 500 key genes required for a yeast to survive. And then he suggested that the identified genes be replaced with equivalent human genes. The same genes that manufacture cholesterol, and keep the cells in shape. And after 3 years of experimentation, we found that roughly half of these genes can be replaced with the human version. Many of the essential cellular processes that happen in yeast and humans are the same. Marcotte concluded that about 1 billion years ago, yeast and humans had a common ancestor. And this is where the story reaches LUCA, the Last Universal Common Ancestor, which I talked about in the last video. In the last video, I told you that there are about 355 genes that are found in all types of existing life forms. I want to clarify a small point here. Scientists have found only 30 common universal genes which are found in all types of genomes. But they were not sufficient to tell us where and how LUCA lived. So, the University of Dusseldorf's professor Bill Martin
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and his 6 associates adopted another tactic. They looked at the ancient genes of bacteria and archaea and found that there were actually 355 genes in common. And just like that, if we kept going backwards, we reach FUCA. The First Universal Common Ancestor. As I told you, life began in water when some free-floating nucleotides were assembled in RNA. But it's not as if these nucleotides had fallen from the sky. The Earth was formed about 4.5 billion years ago. And before that, our solar system was just a cloud of interstellar gas and dust. Think of a cloud known as a solar nebula. Probably a big star like a Supernova must have exploded near it. Releasing shockwaves. And then that cloud slowly settled into the Sun and the planets were formed. And that is why it is said that all of us are made of Stardust. All humans, animals, plants, the ground, the sky, everything is made of Stardust. This is the whole story of evolution. Stardust, FUCA, LUCA, Prokaryotes, Eukaryotes, Multicellular organisms, Bilateral worms, Vertebrates, Tetrapods, Mammals, Primates, Hominins, and finally Homo Sapiens. Some people don't accept this and I can understand why. Because it is so difficult to imagine that everything, all life must have originated from this small cell. And that cell must have been made of some nucleotide. But I can help you a little with your imagination. It is not as strange to imagine this thing as you might think. Think for yourself how a human is born. When some genetic material present in a man's sperm, mixes with the genetic material of a woman's egg. A zygote is formed; a fertilised egg. This zygote divides through mitosis, and two cells are formed, then four cells, then eight cells, then sixteen cells, then a small ball of cells is formed. By the sixth day, we see a Blastocyst, which is a hollow ball and has inner cells, outer cells, and some fluids. When the shell breaks, the blastocyst is released and gets implanted by attaching to the uterus. Later, the placenta starts developing which nurtures it. Then eventually we see the major organs and body system being formed. Brain, spinal cord, four-chambered heart, eyes, ears, lungs, liver, red blood cells, hair follicles, knees, toes, mouth, lips, intestines. By the 8th week, the embryo starts looking like a human. But it is still about an inch in size. We call it a Foetus. Moving forward, in the first week of the 10th month, a human child is born. Now think about it, all of it started with a zygote. A minute fertilized egg. And this small egg, how did it change to many different organs, hair, hands, legs? Obviously, evolution is not like this. Evolution is not a human pregnancy. But I am giving you this example so that you can understand the comparison. Because you might be thinking, how can humans evolve from fish? And bacteria? In the same way, exactly like this. When a small cell can transform into so many organs, then evolution can also work in the same way. I hope you are understanding things better. But if you still have any doubts, you can ask in the comments below. And if you want a part 3 of Evolution to clear your other doubts, you can let me know in the comments below. For now, if you liked this article, you can watch part 1 of Evolution, if you haven't already. you can click here https://latestaroundour.blogspot.com/2023/05/Theory-of-Evolution.html to read the article on Evolution.
Thank you very much!
