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Why did anthropoids like us evolve?



Why did anthropoids like us evolve? Animal life existed on Earth for more than half a billion years before the appearance of human beings. But what factors caused the emergence of us and our ancestors?

Why did anthropoids like us evolve?

More than half a billion years of life on Earth have gone by without the appearance of a creature like the wise man: a branch of bipedal tailless apes with tiny teeth and big brains that enabled us to invent new tools and form large social networks. Let’s work together.

The emergence of humans is an important turning point in evolution, or at least it seems so to us. Not only do we want an explanation for our existence, but we want that explanation to be sufficiently prominent and legendary.

A new study reveals an unexpected topic about human evolution. In a word, competition between members of the human race seems to have given rise to new species. It’s weird and complicated, but it doesn’t negate some of the existing stories about our origins. In short, this is the story of how evolution works.

Drivers of evolution

The study cited was published in April in the journal Nature Ecology & Evolution by Laura van Holstein and Robert Foley of the University of Cambridge. They tried to find out why the new species of hominids evolved.

In other groups of animals, evolution usually follows recognizable patterns. One of these patterns is speciation dependent on negative diversity; It means that if there are many species in a group, the possibility of creating new species in that group is less.

Suppose there are many different species of sparrows living in an area. There are many ways to live as a sparrow, and the existing species go all of them. Therefore, new sparrow species rarely evolve. But if there are only one or two species, there are many opportunities so that they may become abundant new species.

The described rule is not absolute, a study from 2023 showed that the said rule is not true in many animal groups. But for some groups, such as birds, there is acceptable evidence to support it. So Van Holstein and Foley wondered if the same was true for hominins. If many anthropogenic species live in an area, does it become less likely that new species will emerge?

Southern reconstruction of the Afari copyReconstruction of Australopithecus afarensis.

The researchers focused on three genera (orders) of anthropoids. The first genus is Australopithecus, or Southern Copy, which includes a variety of hominids that lived in Africa about 4 million to 2 million years ago. Second, it was paranthropus or populous; A small-brained hominid that survived into the age of large-brained hominids and is the third human lineage, which includes our species as well as famous species such as Neanderthals and Flores. Four other hominin genera were excluded due to lack of data; Because there were not enough samples to ascertain the duration of existence or the number of species of each genus.

Van Holstein and Foley used two data sets to estimate how speciation changed. One was the family tree of the anthropoids, which showed how different species were related. Another thing was the fossils and their approximate age. Both datasets had shortcomings and large uncertainties but yielded the same results.

Competitive people

In Australopithecus and Paranthropus, greater species diversity means fewer new species evolved. According to Van Holstein, this is the classic pattern that exists. But in the human race, this process is reversed and we see speciation dependent on positive diversity.

It seems that the competition between the members of the human race has caused the emergence of new species

The higher the number of species, the higher the rate of speciation. In other words, when several species of the human race lived near each other, they were under pressure to evolve, and the possibility of new species becoming more likely.

The above pattern is unusual. Similar patterns have been confirmed in only a few species, such as cockroaches that live on islands. Therefore, it seems that the dynamics of evolution in the human genus is significantly different from the pattern of evolution of other anthropoid species and are generally unusual in the animal kingdom.

What is the reason for this? There are several possible explanations. One possibility is range expansion. As far as we know, the human race was the first human species to spread beyond Africa. This could have created many opportunities and helped form new species: think Luzonian Man in the Philippines and Floresian Man on the island of Flores in Indonesia.

Why did members of the human race manage to expand their range, while other hominids did not? Wasn’t it because they made more or better tools?

Technology can also be part of the explanation for the evolution of new species. Species that were able to develop new tools, for example by accessing food that others could not, were able to occupy new habitats.

“I don’t think dispersion explains everything,” Van Holstein says. Speciation is seen in places where other members of Homo are present.

The actions of one human species could also create a habitat for others. Think of water dogs that manipulate their environment by building dams and thus changing the flow of rivers, creating new habitats for insects and other creatures in the process.

If a species of the human race hunted large animals or cut down certain plants, it could create new spaces and opportunities for the evolution of anthropoids. “It changed the landscape and created new dimensions for other people’s lives,” says Van Holstein.

It is difficult to understand the role of each of these factors. But it is clear that the interactions between intelligent people were important not only for the fate of individual populations but also for the emergence of new human species, including ourselves.

Great Narrative

How can we fit interspecies competition in the human genus into the larger story of human evolution? We should also think about the other dominant explanations that have been offered for the fossil record of hominids.

Many of these explanations have to do with the environment: something in the environment changed and this forced hominids to adapt, which led to the evolution of diploidy or larger brains or other traits. One of the famous versions of these environmental narratives is the savannah hypothesis.

Technology can explain the evolution of new species

According to the Savannah hypothesis, the great apes that were our ancestors lived in forests and often climbed trees. But later the climate changed, forests shrank and grasslands spread, so our ancestors had to come down from the trees.

However, the savannah hypothesis has been challenged by the reconstruction of past ecosystems. The expansion of African savannas began before the existence of humans, and many habitats were a mixture of grasslands and forests.

A 2014 paper in its title questioned whether the Savannah hypothesis is a dead concept. However, he concluded that the answer is no, provided you accept that the savanna was not an absolute grassland, but rather a combination of habitats.

In the 1980s, Yale University paleontologist Elizabeth Verba proposed the idea that extreme environmental changes could cause waves of extinction. He suggests that the cold climate two to three million years ago caused the rapid extinction of African mammals and led to the evolution of new species, including hominins. Again, the reconstruction data of past environments contradicts this hypothesis.

In the 1990s, Richard Potts of the National Museum of Natural History in Washington put forward an argument in support of the above hypothesis. The idea here is that Africa’s climate became more unpredictable, so hominins had to adapt to this variability. The best way to do this is to become more adaptable, for example by becoming smarter and more innovative.

If all of the above ideas sound reasonable, that might be because they really are. A 2015 review suggested that multiple evolutionary mechanisms operated on hominins.

This is where Van Holstein and Foley’s study comes in. If hominids faced evolutionary pressures ranging from savanna expansion to unpredictable climates, then interspecies competition must be added to the mix.

The story of human evolution is more like the novel “A Song of Ice and Fire”.

Van Holstein says he is not trying to prove that climatic and environmental factors are unimportant in human evolution. Rather, it says that the environment clearly determines what knames are available. If there is a major climate change and old clades are removed and new clades are established, this changes biological interactions. Importantly, from Van Holstein’s point of view, interactions between human species may be just as important.

So, here we are with a story about the evolution of humanity that has several aspects. Old ideas like the Savannah Hypothesis have the simplicity of a classic myth, which is fascinating and incomplete at best. But the story we are telling is more like the novel “A Song of Ice and Fire” by George R. R. Martin is: too long, too many characters, too many subplots, and so far painfully unfinished.


Who were the anthropomorphs of Denisova?




Who were the anthropomorphs of Denisova? Denisovans are a species of extinct ancient hominids that lived in Siberia, Tibet, and even the Pacific Islands around 200,000 years ago.

Who were the anthropomorphs of Denisova?

Neanderthals disappeared from the world scene around 40,000 years ago. But we, modern humans, are no strangers to these ancient cousins. The stout skeletons of our Neanderthal relatives can be seen in museums around the world. We see their fictional characters in the media and we are somewhat familiar with their habits, lifestyle, and culture. These cousins ​​are very similar to us, and in the distant past, they also mixed with wise humans who spread through Africa in the world.

But we don’t know Denisovans ( deh-NEESE’-so-vans ) as well as their Neanderthal cousins, and that’s probably because the Denisovans didn’t leave many bones. The Denisovans were a group of humans that once separated from the Neanderthals and lived on Earth for hundreds of thousands of years before extinction. Despite very little evidence, many scientists are increasingly fascinated by the Denisovans. But who were the Denisovans?

Table of Contents
  • Discovery of the Denisovans
  • The evolution of the Denisovans
  • Fossil specimens of Denisovans
  • Interbreeding
  • Where did the Denisovans live?
  • When did the Denisovans live?
  • What were the Denisovans like?
  • Culture of the Denisovans
  • Controversies surrounding the Denisovans
  • Why did the Denisovans become extinct?

Denisovans, like Neanderthals, are a group of the closest extinct relatives of intelligent humans. It wasn’t until 2010 that scientists first announced that Denisovans existed and once lived on Earth, so much about these relatives remains unknown to this day. However, fossil and genetic evidence suggests that Denisovans lived in a wide range of regions and conditions; From the cold mountains of Siberia and the highlands of Tibet to the forests of Southeast Asia and even the islands of the Pacific Ocean.

The sculpture of the head and face of a 13-year-old girl from the Denisova prehistoric anthropoid species
The sculpture of the head and face of a 13-year-old girl from Denisova’s prehistoric anthropoid species.

Discovery of the Denisovans

According to Nature magazine, Russian scientists discovered the first fossils related to Denisova in the summer of 2008, in the excavation of a place called Denisova Cave in the Altai mountain range in southern Siberia. In the 1700s, this cave was the residence of a hermit named Denis. For this reason, it is known as “Dennis Cave” in Russian. Denisova also got their name from this cave, because it was the place where the first fossils of Denisova were discovered.

The first fossils of Denisova were discovered in 2008, in the excavation of Denisova cave in Siberia

According to Nature, scientists had discovered a number of stone artifacts in the previous excavations of the Denisova Cave, and based on decades of previous study, they had attributed the origin of these artifacts to Neanderthals. Therefore, when scientists first discovered Denisovan fossils in this cave, they thought that these remains were the same as Neanderthal artifacts.

However, subsequent analysis of ancient DNA extracted from these fossils suggested otherwise. In 2008, researchers sequenced the first complete genome of a Neanderthal, but one of the fossils discovered in the cave was a small piece of finger bone, 30,000 to 50,000 years old, belonging to a completely different and unknown human lineage. In 2010, scientists in a study published in the journal Nature officially announced the details of the discovery in a study published

Chris Stringer, a paleontologist at London’s Natural History Museum, told LiveScience: “Discovering a new species from a tiny piece of finger bone was a remarkable technical achievement.”

A large molar tooth belonging to a DenisovanDenisova’s molars
Photographer: David Reich / Nature

In addition to announcing the existence of Denisovans for the first time, a 2010 Nature study also found the species to be closely related to Neanderthals. A subsequent study published in Nature in 2013 estimated that the lineage that gave rise to Neanderthals and Denisovans diverged from the ancestors of intelligent humans between 550,000 and 765,000 years ago. Later, the ancestors of Neanderthals and Denisovans separated from each other between 381,000 and 473,000 years ago. This means that Denisovans and Neanderthals are the closest relatives of modern humans.

Denisovans and Neanderthals are our closest relatives

A study published in 2018 in the journal Tuberculosis showed that the species of Denisovans consists of multiple relatives. One of these lineages had a close relationship with the Siberian Denisovans. The genetic heritage of this group is found mainly in East Asian people today. The other one was more distantly related to the Denisovans of Siberia, and nowadays it is mostly seen in the natives of Papua and the people of South Asia.

The two Denisovan lineages diverged about 283,000 years ago. Although Denisovans shared a common origin with Neanderthals, they were genetically very different from Neanderthals, almost as much as Neanderthals are from Homo Sapiens . differed

A subsequent study, published in 2019 in the journal Tuberculosis, unveiled a third Denisovan lineage. Based on the level of genetic differences between all three Denisovan lineages, the study showed that this third lineage separated from the other two groups about 363,000 years ago and was almost as different from other Denisovans as it was from Neanderthals. DNA of the third lineage is mainly found in the present-day natives of the island of New Guinea and its surroundings.

Denisova cave in the Altai mountain range in southern Siberia
Denisova cave in the Altai mountain range in southern Siberia.
Photographer: Demin Alexey Barnwell / Wikimedia

Fossil specimens of Denisovans

By 2022, researchers had attributed eight small, highly fragmented fossils to Denisovans based on identified DNA. All eight fossils have been discovered from Denisova cave excavations. The fossils included three molars, a fragment of a hand or foot bone, three small bone fragments, and a fragment of a finger bone; These fossils alone were sufficient to produce the DNA necessary to sequence the entire genome.

Scientists also discovered other fossils in China and Laos that contained specific proteins that they knew belonged to Denisovans based on previous DNA studies of the extinct lineage. The fossils include a piece of jawbone from a sacred site in China and a molar from a cave in Laos.

The remains of Denisovans discovered to date, based on their DNA or proteins, provide few clues as to how fossil Denisovans can be identified morphologically or in appearance. In this way, previous research may have discovered countless Denisovan fossils that remain unknown; Because they have morphological differences compared to other anthropoids that scientists still cannot identify.

The researchers say that the more evidence of Denisovans that is obtained, especially those that cover both DNA and morphological evidence, the more likely it is that other known fossils will be placed in this group.

Ancient molars discovered in Laos
An ancient molar discovered in Laos may have belonged to a three-year-old Denisova girl who lived 164,000 years ago.
Photographer: Dimitar F / Nature

A 2010 Nature study showed that the Denisovans interbred with the ancestors of modern humans , so that about four to six percent of the genome of the natives of New Guinea and Bougainville Island, or the modern genome of Melanesians, is made up of their DNA. Melanesia is a region in Oceania that includes New Guinea, Solomon Islands, Vanuatu, New Caledonia, and Fiji. In contrast, a 2013 Nature study found that only about 0.2 percent of the DNA of mainland Asians and Native Americans is of Denisovan origin.

Denisova’s DNA may have many benefits for intelligent humans. For example, a 2014 study found that a genetic mutation from the Denisovans may have helped Tibetans and Everest natives live at high altitudes. Another study in 2016 found that Denisova’s DNA may have influenced the modern human immune system, as well as our blood fat and sugar levels. Of course, heredity has not come without a cost, heritable DNA may even have increased our susceptibility to schizophrenia and other mental disorders.

Also, by examining the Denisovan DNA that has been inherited by living humans today, the researchers say that the pattern of recorded mutations suggests that several distinct genetic groups of Denisovans intermingled with our ancestors. Furthermore, none of these Denisova groups were closely related to the Denisova Cave-dwelling group.

Several genetically distinct groups of Denisovans interbred with our ancestors

Researchers say that the most interesting results in this field have been obtained from the studies of the people of New Guinea and the Philippines. Signs of frequent admixture of the wise man’s ancestors with the Denisovans can be seen in the people of New Guinea and the Philippines, which differed from the samples from mainland Asia. Experts suspect that when sea levels dropped during the last Ice Age, the Denisovans probably migrated on foot to New Guinea and the Philippines. This means that the Denisovans lived in this place for thousands of years before the arrival of wise men in the region.

Previous studies show that Neanderthals also had intercourse with intelligent humans. A 2013 study estimated that the genomes of all non-African humans contain 1.5 to 2 percent Neanderthal DNA. Additionally, another study in 2018 found that Denisovans and Neanderthals also interbred.

The 2018 study examined a 2.5-centimeter bone fragment unearthed in 2012 from an excavation of Denisova Cave. This small piece was removed from a long bone, such as a tibia or femur. The thickness of the outer part indicates that the bone belonged to a girl who was at least 13 years old at the time of death. Radiocarbon dating shows that this fossil is more than 50,000 years old.

DNA from the fossil discovered the first known Denisovan-Neanderthal hybrid and also showed that Denisovan’s father probably had at least one Neanderthal ancestor between 300 and 600 generations before him. Overall, this discovery revealed several instances of interaction between Neanderthals and Denisovans.

A small bone fragment of a 13-year-old Denisova woman was discovered in the Denisova cave
A small bone fragment discovered in Denisova Cave provides new evidence of interbreeding between Denisovans and Neanderthals.
Photographer: Thomas Heim / University of Oxford

In addition, the scientists found that the teenage girl’s Neanderthal mother was genetically more similar to Western European Neanderthals than to other Neanderthals who lived in Denisova Cave. This finding shows that Neanderthals were migrating between West and East Eurasia for tens of thousands of years.

So far, scientists have sequenced the genomes of six Denisova cavemen. According to the researchers, the findings based on the fact that one of these six people had a Neanderthal parent and a Denisovan parent, from a statistical point of view, show that admixture was very common when these two groups interacted with each other.

Where did the Denisovans live?

The evidence found paints a fascinating picture of humans who could have thrived and expanded in diverse environmental conditions, from cold Siberia to the highlands of Tibet, the jungles of Laos, and perhaps even the islands of the Pacific Ocean. The Denisovans were in competition with us in terms of adaptability and adaptability.

Modern humans left Africa about 60,000 years ago, at that time the Denisovans were probably on their way, and they may have donated some of their genes to us through interbreeding. But in 2019, scientists found the first Denisovan fossil in a place beyond Siberia, in a cave in the highlands of Tibet.

Denisovans were similar to us in terms of adaptability and adaptability to environmental conditions

Researchers discovered part of a jaw more than 160,000 years old and teeth similar to Denisovans in a cave in Tibet. The fossil contained proteins with a molecular structure similar to the genes of Denisovans. The following year, researchers reported that the cave floor sediments also contained Denisova’s DNA.

By 2022, scientists had discovered Denisovan remains at archaeological sites in Siberia, China, and Laos. The discovered fossil data matched the genetic evidence of Denisovans found in modern Melanesian humans. Also, fossil evidence of Denisovan jawbones discovered in the Tibetan Plateau also shows that a group of Denisovans were adapted to living in high altitudes and cold climates.

Overall, the findings show that the Denisovans lived in very different environments. They endured the harsh winters of Siberia and the thin air of the Tibetan Plateau. In Laos, they lived and hunted in open forests with herds of pygmy elephants and other mammals. Based on DNA evidence, they may have also lived in the rainforests of New Guinea and the Philippines.

Digital reconstruction of Denisova fossil mandible discovered in TibetDigital reconstruction of Denisova fossil mandible discovered in Tibet.
Photographer: Jean-Jacques Hublin / MPI-EVA

When did the Denisovans live?

According to the 2010 Nature study that first discovered the existence of the Denisovans, the Denisovans lived in the Denisova Cave between 30,000 and 50,000 years ago.

But in another study published in 2021, scientists claimed that the oldest Denisovan fossils discovered so far are about 200,000 years old. These 200,000-year-old bones were also discovered in Denisova Cave.

Overall, the findings show that the Denisovans lived on Earth at the same time as Homo sapiens and Neanderthals and were their closest relatives.

What were the Denisovans like?

A study in 2019, examining Denisova’s finger bone discovered in Denisova Cave, described her appearance and showed that this bone belonged to a teenage girl aged about 13.5 years. Another study also showed that this Denisova girl had dark skin, brown hair, and brown eyes.

Like Neanderthals, Denisova’s daughter may have a short forehead, a protruding jaw, and a very small chin. However, the dental arch of Denisovans may have been much higher than that of us and Neanderthals. That is, the rows of their upper and lower teeth are more prominent, and the upper part of their skulls is also significantly wider.

The first portrait of a 13-year-old Denisova woman reconstructed from ancient DNA
The first portrait of Denisova’s 13-year-old daughter was reconstructed based on an ancient DNA sample.
Photographer: Mayan Harel / Cel magazine

Denisovans were more like Neanderthals

Differences aside, it’s difficult to understand exactly what Denisovans looked like, as there is very little fossil evidence of Denisovans available to researchers. But in general, Denisovans are expected to be more like Neanderthals than us, researchers say, because the two groups were more closely related than we are.

For example, from the relatively close evolutionary relationship of the Denisovans with the Neanderthals, we can guess that they had a large body and a large brain. In addition, the researchers expect that societies living in regions with cold climates (although not all of them) have massive trunks and relatively short and broad bodies. The researchers add that by further examining the Denisovan genome, the prediction of their appearance will also be more advanced.

Culture of the Denisovans

In 2021, scientists discovered the first Denisovan stone tools in the Denisovan Cave in Siberia. According to a study published in the journal Nature, these works belong to the oldest Denisovan fossils discovered to date.

In that study, researchers examined 3,791 bone fragments discovered in Denisova Cave. Based on previous DNA studies of Denisovans, they looked for proteins they knew belonged to this extinct lineage. Later, scientists discovered three bones of Denisova in the cave. Based on the layer of earth in which the fossils were discovered, the team determined that the fossils were about 200,000 years old.

The soil layer also contained a treasure trove of stone artifacts and animal remains that may serve as vital archaeological clues about the life and customs of the Denisovans. Previously, Denisova fossils had only been found in layers that did not contain any archaeological material, or in layers that also contained material associated with Neanderthals.

Denisova's bones discovered in the Denisova cave in SiberiaBones of the Denisovans were discovered in the Denisova Cave in southern Siberia.
Photographer: Katrina Duka / Nature

The findings showed that the bones of these Denisovans belong to the time when the climate of the region was warm and similar to today. At that time, the region was suitable for human life with broad-leaved forests and open steppes, grasslands, savannahs, and temperate shrubs. The remains of butchered and burned animals found in the cave also indicate that the Denisovans probably fed on deer, deer, horses, bison, and woolly rhinoceros.

The stone artifacts found in the same layer of Denisova fossils are special tools for shaving and maybe they were used for tanning animal skins. The raw materials for making these items probably came from the sediments of the river, which is located just outside the entrance of the cave. The river also served as a source of water and also drew prey to the cave.

No equivalents for these stone tools and associated fossil artifacts have been discovered in North or Central Asia. However, the study’s authors noted that the items bear similarities to items found in Israel, which date from 250,000 to 400,000 years ago; A period associated with major changes in human technology, such as the common use of fire.

Controversies surrounding the Denisovans

In 2021, three controversial studies published in the journal Invention claimed that a fossilized skull discovered in China nicknamed “Dragon Man” that is at least 146,000 years old belongs to a new species called Homo Longi . However, many scholars argue that the Dragon Man may actually be just a Denisova.

The 146,000-year-old fossil of Dragon Man is one of the largest extinct human skulls. The brain inside the skull could have been similar to that of a wise man, but the bony sockets of the eyeballs in this skull were larger and almost square than in modern humans, the brow ridges were very thick, the mouth was wider and the teeth were larger than normal.

The Dragon Man fossil may actually be Denisova

One of the authors of the 2021 study says that other ancient hominin fossils discovered at archaeological sites in China, such as Dali, Jinyushan, Xiahe, and Hualongdong, may belong to the same group.

All in all, scientists say the dragon man’s skull has a mix of ancient and modern human features that distinguish the species from other known members of the Homo family, a lineage from the human family. However, until scientists discover more fossil and genetic evidence of Dragon Man and Denisovans, it cannot be confirmed or denied that the two are the same.

Illustration of a 146 thousand year old dragon man
The illustration shows what Dragon Man looked like 146,000 years ago.
Photographer: Chuang Zhao / LiveScience

Were hobbits also Denisova?

In 2021, another study was published that claimed two lineages of extinct hominins with miniature bodies may have been Denisovans. One of these groups is called Homo Floresiensis and we often know them as “Hobbits”. Another group, which is smaller, is known as Homo Luzonensis.

Both groups of Floresians and Luzonians were alive until about 50,000 or 60,000 years ago and may have lived in the islands of Southeast Asia at the same time as the Wise Men.

Modern humans from Southeast Asian islands have relatively high levels of Denisovan DNA. At present, there is little information about the anatomy of Denisovans and the genetics of Floresian and Luzonian humans. For this reason, it is also possible that the extinct small humans were the same Denisovans who intermingled with modern humans in the islands of Southeast Asia.

However, other scientists do not agree with this conclusion. They note that, based on archaeological evidence, the two groups of Floresian and Luzonian humans lived in the islands of Southeast Asia at least 700,000 to 1 million years ago, long before the Denisovans first evolved. Hobbits and their cousins ​​may be too ancient to be Denisova.

Why did the Denisovans become extinct?

The Denisovans one day disappeared from the face of the earth, but their genetic legacy lives on in living humans. However, it is not yet known exactly why and how the Denisovans became extinct.

Scientists say that the Denisovan overlapped with the expansion of the intelligent human population sometime between 40,000 and 50,000 years ago and the subsequent competition for limited resources was probably one of the reasons for the Denisovan extinction.

Also, Denisovans may have drowned in our species’ gene pool. But in general, the researchers say that this issue remains “unanswered” until today.

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Why do most mammals have five fingers?




Why we humans and most other mammals have five fingers is a simple question that has baffled scientists from several disciplines, But there is still no clear answer.

Why do most mammals have five fingers?

If you look at the paws of a cat, dog, or even a kangaroo, you will notice that they have something in common with our hands. All these mammals have five toes, even if some of those toes are smaller or in different positions. Why do we share this trait with our furry friends, even though we evolved under different conditions?

To answer the question of why mammals have five toes, we must first understand why four-legged vertebrates have five toes. Mammals belong to the order of tetrapods, which includes reptiles, amphibians, and birds. Even members of this group that do not have traditional limbs have five toes in their skeletons, whales, seals, and sea lions have five toes in their flippers, even if they have four or fewer toes.

There are differences among tetrapods. Horses have only one toe and birds have a finger bone at the end of their wing. Scientists have discovered that these animals are formed with five fingers during the embryonic period, but before birth, the other fingers shrink and disappear.

The forelimbs of mammals, including the human arm, the forelimb of a lion, the forelimb of a whale, and the wing of a birdVertebrate forelimb, bird wing, human arm, lion forelimb, horse forelimb, frog hand, and whale forelimb.

Thomas Stewart , an evolutionary biologist at Pennsylvania State University, told LiveScience that the process of finger formation is mainly controlled by Hox genes. Hox genes encode proteins that help regulate the activity of other genes, turning them on or off. They help to ensure that body parts fit properly as the fetus develops in the animal’s body.

Hox genes also play a role in the skeletal pattern of quadrupeds, and they do this by helping to control proteins made by the sonic hedgehog gene to turn each other on and off while building tissue.

Read more: Octopuses and humans shared a common ancestor hundreds of millions of years ago

Through the process of gene control, finger buds grow. Depending on the animal, these buds can continue to grow or be reabsorbed. Then, the surrounding cells, where the fingers should be, die and form separate fingers. According to Stewart, the exact details of how this happens vary depending on which scientist you ask.

No one is sure when this five-finger design first evolved. Stewart said the first known animals to grow fingers evolved from fish about 360 million years ago and had eight fingers. However, the presence of the five-toed plan in most living tetrapods suggests that this feature is probably a “homology” or “homomorphology”; That is, a gene or a structure that is common between organisms because they are rooted in a common ancestor. The common ancestor of all living quadrupeds must have somehow evolved five toes and passed this pattern on to its descendants.

Three giraffes in the Maasai Mara National Reserve, Narok County, KenyaGiraffes and humans have seven neck vertebrae.

A common ancestor explains how mammals got five fingers, but doesn’t tell us why. One theory is channeling; It means that with the passage of time, a gene or trait becomes more stable and the probability of its mutation decreases. Stewart gave the example of cervical vertebrae: Mammals almost always have seven cervical vertebrae, even if this number does not seem to be particularly advantageous. According to this theory, if this number has worked for millions of years, there is no reason to change it.

Not all researchers agree with the channeling theory. ” Polydactyly,” or having more than five fingers, occurs as a mutation in many mammals, including humans, says Kimberly Cooper, an evolutionary geneticist at UC San Diego. There are many mutations that can cause polydactyly, but a study recently published in the journal Nature showed that polydactyly can be caused by a single nucleotide mutation in the hedgehog’s sonic gene.

“If the answer is that easy, why aren’t there any polydactyl species?” Cooper asked. He argues that the absence of these species is because polydactyly is an evolutionary disadvantage.

Some suspect that this may be related to gene linkage: as genes evolve over millions of years, some become linked, meaning that changing one gene (finger size) can lead to more serious health problems; But so far no one has given a specific reason.

“It might seem like the answer to the simple question of why we don’t have more than five fingers should be simple,” Stewart said. “But it’s a very deep issue that makes it really exciting to study.”

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Which ancient humans can be seen in our DNA?




Which ancient humans can be seen in our DNA?

Which ancient humans can be seen in our DNA? Our ancestors had sex with ancient humans including Neanderthals; But researchers have found DNA traces of previously unknown species in our genome.

Which ancient humans can be seen in our DNA?

In 2010, when the Neanderthal genome was first sequenced and compared to that of modern humans, scientists discovered that Neanderthal genes are also present in our DNA. The conclusion was very simple: our ancestors had intercourse with other humans who are now extinct, and now the genes of these humans remain in us.

In 2012, when Denisova’s human genome was also sequenced, it revealed another example of interspecies mating. Now we know that small populations of all three human families have interbred at different times; Thus, the DNA of our modern humans (homosapiens) today has something in common with groups of ancient hominids that once lived next to us; But they could not survive until today. However, the genes of Neanderthals and Denisovans have not remained in the DNA of all humans. For example, Africans have none of these genes; While Europeans have the genes of Neanderthals. However, these genetic echoes are not clear enough for scientists.

Which ancient humans can be seen in our DNA?

A copy of a finger bone fragment from a Denisovan in the Museum of the History of Science in Brussels, Belgium. This bone was discovered in 2008 in Denisova Cave, Siberia.

Neanderthals and Denisovans were the closest extinct relatives of our modern humans, who diverged more than 390,000 years ago. The Denisovans left Africa before the ancestors of modern humans and spread across the planet, living in Asia around 30,000 to 50,000 years ago. Recent findings show that all human populations outside of Africa have 1-2% Neanderthal DNA, and the DNA of Australian and Melanesian aborigines has 5% Denisovan DNA.
The presence of DNA from other human groups in us modern humans is not so surprising; Because today’s Homo sapiens are the result of millions of years of evolution. We can name several species of ancient anthropoids as our ancestors, But the participation of Neanderthals and Denisovans in our genetic makeup has just happened; That is, after homosapiens separated from other human groups.

These interbreedings, which are called introgression, did not create a new human species; Rather, it has only led to the enrichment of some traits that already existed. We still feel the presence of some of the traits that we have acquired in this way in our lives today.

Adam Seipel, a computational biologist at Cold Spring Harbor Laboratory (CSHL), says:

There is a lot of evidence of interspecies interbreeding between ancient humans and modern humans, especially modern humans outside of Africa; Therefore, there is no doubt about this. Some evidence shows that there may be genes from more than two other anthropoids in our DNA, which some researchers sometimes refer to as ghost lineages. Modern humans living in Africa probably interbred with several ancient human species, adding more genes to our current DNA.
A recent study on the people of Indonesia showed that what we call the Denisovans were actually three separate groups of anthropoids, each of which could be called a separate species. It goes without saying that the ancestors of Asians and Melanesians interbred with at least one of these groups and probably more.

Dark Ghost Hunt

Scientists try to reveal the complex past of us humans in various ways. Such a task would have been easier for species such as Neanderthals and Denisovans, whose DNA is still preserved in fossils. After sequencing the genomes of these ancient humans, archaeologists compared their genomes with those of us today. The great similarity of our DNA to some ancient species is proof that our ancestors had intercourse with these hominids.

However, these genes can originate from a more distant past; For example, maybe from the last common ancestors we had with Neanderthals and Denisovans. However, this split happened a long time ago; So most of the DNA regions we share with other human groups have experienced mutations that have caused the separation of these traits from each other in each group of humans. However, each of these genes is a strong indicator of inter-racial admixture.

Which ancient humans can be seen in our DNA?According to researchers’ modeling, about 2% of the African genomes that were sequenced originated from an unknown ancient human or the “dark ghost”.

With all this, we should know that scientists have bones or rather fossils for most of the ancient species that we know now, and it is rare that they can find evidence of the DNA of these ancient humans. The problem is that the molecules that make up the nucleic acid helices have been destroyed over time, especially in hot and humid environments; Environments where most of our ancestors lived. However, archaeologists have tried to fill this void of ancient human DNA through statistical modeling. Several studies have also shown that these mysterious ancestors were hidden in our genome; However, the error rate is also high in such simulated models.

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Several studies have shown that mysterious ancestors were hidden in our genome

The mathematical models used by scientists to find ghost families in genetic data are complex, But they are often enough to search for gene clusters in specific human groups today. Recently, a group of researchers did such work and examined a set of 161 genomes of the present-day residents of Indonesia. The researchers compared this genetic information with the genomes of Denisovans, Neanderthals, and other modern humans.

Which ancient humans can be seen in our DNA? Neanderthal skull that was discovered in 1908 in the ancient cemetery of Lachapel-Assins in France.

Researchers found signs of Denisovan DNA in Indonesian residents, which was not surprising; But the researchers found that these ancient humans were actually three separate groups. These three groups had common ancestors; But when they were scattered in different parts of Asia and the Pacific Ocean, they started to separate from each other. The group whose evidence was found in Siberia was as different from another group as a Denisovan is from a Neanderthal. For this reason, even some researchers declared that this group can be considered a separate species; But fossils of this group have not yet been found to officially prove this assumption.

Murray Cox, a population geneticist from Massey University in New Zealand and lead author of the study, said:

All in all, this new genus of Denisovans is so different from the Denisovans found in Denisovan Cave that if we are going to give different names to Neanderthals and Denisovans, this new group probably needs a new name as well. Therefore, the new findings may give us concrete evidence of this Denisova cousin; But for now, the only clue is a fragment of DNA that remains within the genome of some of us modern humans.
However, these ghostly Denisovans are not alone. Other researchers are also studying the DNA of African hunter-gatherer tribes to find evidence of our ancestors mixing with these tribes tens of thousands of years ago. Perhaps the biggest study of this kind is the research whose results were announced in 2011, in which researchers examined the DNA of 61 Africans from the Mandanka, Biaka, and San tribes. They compared these genomes with two human population models, one of which showed that African ancestors had interbred with human groups; But other comparisons did not show this. This model, which consisted of gene migration (Gene Migration) of ancient humans, obtained results that were more consistent with the real population of the inhabitants of the region.
The researchers announced that based on this modeling, about 2% of the African genomes they sequenced originated from an unknown ancient human. These two groups intermarried about 35 thousand years ago. In another study, researchers evaluated a gene called MUCL7. This gene secretes a protein in our saliva that keeps the mouth moist during chewing, talking, and swallowing and kills some harmful bacteria.

Thus, the researchers were able to find more evidence of the ghost race in Africa. The MUCL7 gene exists in humans today in several variants, and researchers say that it can be attributed to one of the unknown ancient ancestors of humans. Also, in a study in which the genomes of 15 people from the Hadza, Sandui, Baka, Bakula, and Bizen tribes in Africa were examined, evidence of interspecies intercourse was discovered. However, the researchers could not identify the target species.

The Heritage of Modern Humans

The genes that many of us inherited from other human species are still active in our bodies today. The genes of Neanderthals and Denisovans already affect the functioning of our immune system. It is thought that Neanderthal genes affect the body’s keratin, which makes up our hair and nails, and the way the body reacts to UV rays. We modern humans probably got these genes after migrating from Africa to Europe; Where interbreeding with our cousins, the Neanderthals, may have helped us quickly adapt to colder climates.

Which ancient humans can be seen in our DNA?

The entrance to the Denisova Cave in the Altai Mountains of Russia. The first remains of Denisovans and the bones of Neanderthals and modern humans were also discovered in this cave.

This issue is even more surprising in the sense that other populations adapted to life at high altitudes, including the natives of the Andes Mountains in South America and the highlands of Ethiopia in Africa, have achieved such adaptations by increasing hemoglobin. In fact, this adaptation has been done in a different way in Tibetan people. Instead of increasing the number of hemoglobin, Tibetans’ bodies have acquired other adaptations that allow them to use oxygen effectively. This adaptation to a relatively low hemoglobin count at high altitude has prevented the occurrence of the negative aspects of a high hemoglobin count. A high concentration of hemoglobin and as a result thickening of the blood increases the possibility of blood clotting, which, as a result, increases the risk of heart disease and stroke in a person.

There was much more diversity among ancient humans than we previously thought

However, other genetic factors have caused problems. Some Neanderthal genes have been implicated in the occurrence of depression, heart attack, and allergies. While some genes left over from ancient species helped our immune systems, others may have predisposed us, modern humans, to diseases such as systemic lupus erythematosus (an autoimmune disease), Crohn’s disease (an inflammatory bowel disease), and type 2 diabetes.

As with most family inheritances, further understanding of the genetic inheritance of Homo sapiens is more complex. Scientists need to do more research before they can understand the true implications of our multispecies past. In fact, even finding evidence of these ghostly clans can be problematic.

Distinguishing a ghost from an illusion

The dark evidence of the ghost is gradually forming; But when scientists rely solely on genetic evidence, it is clear that they will not be able to prove the existence of a species. There are several factors that can make what we have learned from the remaining genes of ancient humans look completely wrong. For example, what kind of evolutionary pressure the population is under, and things like genetic bottlenecks (an event where only a fraction of the population survives to reproduce) add to the skepticism about purely genetic studies. Thus, what sometimes appears to be a ghost may be nothing more than a curtain flapping in the wind!

A recently published research has clarified some of the shortcomings of this method. In this study, three researchers from Spain and Estonia announced that based on complex statistical analyses and machine learning algorithms, they found evidence of the ghost race in the DNA of Asian and Pacific people.

These researchers first simulated the artificial genome using a computer program and then compared it with population models of ancient humans. Oscar Lau, one of the team’s researchers and a population geneticist at the Center for Genome Regulation in Barcelona, says he and his colleagues ran these simulations millions of times. The researchers then looked at the evolutionary history of the artificial genome to find out what in this genome led to the formation of the gene cluster. On average, the results of more than a million simulations provided scientists with a model they called the equivalent of “a real genome.”

A man loads ice cubes into a truck in Yakutsk, Russia. Interbreeding with Neanderthals may have helped us adapt quickly to cold climates.

This information finally provided researchers with several different modes of interaction between different races of ancient humans. One of the best simulations, they said, was a model of a previously unknown ancient race that had interbred with modern humans. The researchers said that these humans were probably a hybrid race of Neanderthals and Denisovans. Also, this modeling could explain why present-day Asians have inherited more Neanderthal DNA than Europeans. In fact, according to the researchers, the ancestors of Asians have had intercourse not only with Neanderthals but also with another hybrid race. Lao said in this regard that this research once again shows us that human beings are different species and families. He added:

Our findings show that there is a lot of complexity in the genetic diversity of ancient anthropoids. Not only did Neanderthals interbreed with early modern humans; Rather, but other ancient humans have also interacted with modern humans, of which no evidence remains.

While this narrative is interesting in many ways and clearly supports the findings of hybrid humans that were discovered last year in Denisova Cave in Siberia; other researchers are not so convinced. Last August, researchers published the results of their investigations on the bone fragment. Their findings showed that what they had examined was actually the remains of an ancient female hybrid of a Neanderthal mother and a Denisovan father. Earlier in 2012, Russian archaeologists discovered this bone. In their analysis, the researchers found that this bone belongs to a 13-year-old girl who died almost 90,000 years ago. The Denisovan species itself had been discovered two years earlier in 2011 from unusual hominin DNA found in bones found in the Denisovan Cave in the Altai Mountains of Russia in Siberia.

These findings of his are at least generally consistent with the assumption that the Denisovans were more than a species. If so, Cox and Browning may have found evidence of the same specter that was distantly related to the Denisovans, or they may have each found different groups, making it clear that there was far more diversity among ancient humans than previously thought. We used to do it, there has been.

Future research

While scientists claim to have discovered evidence of previously unknown species that had something in common with us in the past, it is reasonable to ask how much such evidence we might find in the future, and what evidence of ghost races we have so far that could support their existence. ? In fact, we may have already passed the range of observable DNA from our ancestors. The DNA of Neanderthals and Denisovans make up only a fraction of the genomes of today’s modern populations. Any extrapolation present could be a small part of our DNA, Browning says. He continues to add that most of the DNA parts that seem to have come to us from other species have probably been found; therefore, there is not much left to work on.

Future archaeological findings can surprise us by providing definitive and reliable evidence; Especially to be able to extract the DNA of the discovered remains. For example, the evidence of Denisovan DNA in our genomes is likely to be too minute to sequence, Seipel says.

He says:

I’m sure if we just try to prove the existence of this species by assuming the existence of minor outbreeding in modern humans, we will enter into a very controversial discussion.
Future findings may turn today’s ghost races into tangible species that were once living, breathing humans; Humans who have left their genetic history in us. Their bodies may be gone, But their DNA is alive.

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