01
Since ancient times, humans have wondered what their "original" ancestors looked like. Based on this, many fantastic ancient human beings have been conceived, and almost every nation in the world has its own legend of "gods and immortals creating people".
However, no matter what era human society is, there will be some wise people who can see through the truth.
Plato and Aristotle
As early as the 5th century BC, two ancient Greek philosophers, Plato and Aristotle, proposed the earliest ideas about the origin of mankind:
The whole of nature, including humans, is a complete system. This means that humans and other animals must have originated in the same pattern.
Lucretius
In the 1st century BC, the Roman philosopher Lucretius pointed out in his book On The Nature of Matter:
The earliest humans, unlike the Romans, lived a burrowing life like animals, neither making tools nor using language.
Darwin
Of course, these "niche theories" are usually unpopular and have long been suppressed by religious theocracy. It was not until 1871 that the British biologist Charles Robert Darwin published The Origin of Man and Sexual Choice. In this book, his theory of species evolution completely overturns all myths and legends about the birth of man:
Darwin believed that with the vast amount of evidence he had gathered, it could be deduced that human beings were also governed by the principle of evolution — natural selection.
However, when Darwin had just proposed the theory of evolution (the origin of species) in 1859, he attracted severe criticism: because according to the "hybrid theory" of genetics at that time, the traits of living things black plus white got offspring gray, ash and gray appeared offspring less ash, and so on, the traits became more and more monotonous, there could not be many traits to choose from, so natural selection did not exist.
Mendel
Just when Darwin was struggling to further explain the theory of evolution, in 1865, the Austrian biologist Gregor Mendel used the pea hybridization experiment to reveal the basic laws of the mysteries of biological genetics:
After testing nearly 30,000 pea plants before and after, Mendel finally concluded that the hybridization trait of peas in the offspring series had a separation ratio of 3:1.
Mendel believed that if the offspring were simply synthesized of the traits of the parents, then the traits that all organisms would repeat would tend to be the same, which is obviously inconsistent with the diverse and colorful nature of the species.
Based on this idea, Mendel discovered two major laws in the theory of biological genetics:
One is the law of separation: the pairs of genetic factors that determine the same trait are separated from each other and independently passed on to future generations;
The second is the law of free combination: genetic factors that determine different genetic traits can be freely combined.
"Mathematics is like a razor in a carpenter's shop."
Darwin and Mendel
Darwin did not have mendel's solid mathematical skills, he was a biologist who grew up as a naturalist and had always had a disdain for mathematics.
However, Mendel used mathematics, an important tool, to look at the problem in a simple and simple way, and to extract the cocoon from the complexity and diversity of nature to derive the great laws of biological inheritance.
Not only that, but Mendel also made a large number of annotations in the German translation of Darwin's "Origin of Species", hoping to provide a genetic theoretical basis for Darwin's theory of evolution, and Mendel deduced from his own discovery of the law of free combination of multiple traits:
If there are 7 pairs of pollinating between two plants with different traits, many different combinations can be produced. Simply put, the larger the population of a species, the greater its genetic diversity, that is, all living things have diversity.
Well, this conclusion can complement Darwin's theory of natural selection and survival of the fittest.
The discovery of truth often subverts people's previous understanding, and even breaks the confinement of religious forces.
The combination of genetics and evolution gave rise to molecular biology and recombinant DNA technology, which in turn gave rise to a new discipline that could reveal the essence of life, the life sciences.
The development of life sciences to this day, has been able to use fossils to determine the evolutionary process of human beings, with DNA as a carrier to establish human evolutionary lineage. But few people know how scientists found the earliest fossil of the human ancestor.
02
In fact, fossil formation requires extremely stringent environmental requirements, so where can paleoanthropologists find these fossils?
First, it takes long enough to form a fossil. The current known evolutionary history of humans is about 6 million years, which is only enough time for the skeletons of early humans to form fossils.
Second, the bones need to be kept in a place covered with sediment, or washed into such an area by a river.
More importantly, the movement of continental plates also coincidentally allows these strata of preserved bones to be lifted, so that they are exposed to the land.
chimpanzee
As early as the 19th century, Darwin deduced that chimpanzees and gorillas closest to human kin lived mainly in Africa, and that human ancestors might have lived there as well. And it is true that to this day, Africa is also the best place to search for human origins.
Of course, researchers can't search all parts of Africa for human fossils. So are there any specific areas where there are shortcuts?
The main goal of paleoanthropologists is to look for rock formations exposed by natural erosion.
This type of rock formation, called tuff, is exposed by a combination of continental plate tectonic movements, volcanic activity, and weathering and erosion within rift valleys.
The Oldaway Gorge in Tanzania, Africa, is a well-known rift-grain topography, where tectonic movements and erosion expose layers of tuff containing human fossils.
While many people can understand terrains such as the orogenic uplift caused by plate collisions to form Similar to the Himalayas, and the subduction of plates that lead to the formation of unfathomable Mariana Trenches, there is a lack of understanding of other vertical crustal activity, "settlement".
This is because the Earth's surface is always in a dynamic equilibrium of weathering → accumulation. In areas where subsidence occurs, the surface slowly sinks, forming a depression on the landform, which then merges into a lake. Then the remains are easy to form fossils here.
In other words, those living in non-geological sedimentation zones are equivalent to living in weathering and erosion zones of strata that are difficult to preserve, and are difficult to preserve as fossils on large time scales. Even if the fossils are buried in the ground in a relatively short period of time, they are easily damaged due to long-term weathering and erosion.
The Ethiopian section of Africa's Great Rift Valley is one of the youngest geological sedimentation zones on Earth. The Altwi Gorge mentioned above is an east-west canyon located in the Great Rift Valley of East Africa, which is about 50 kilometers long and about 900 meters deep.
The formation of the Great Rift Valley is quite complex, 30 million years ago, when the junction of the African Plate and the Indian Ocean Plate stretched and drifted in the opposite direction, the crust would bend and rupture to form a fissure, the area between the fissures would sink downwards, and the crust on the periphery of the main fault would rise upwards, forming the bottom and wall of the rift valley.
The bottom faults of the rift valley are usually so deep that liquid material from the Earth's core gushes out through these faults. Under very high pressure, the Earth's molten core will erupt like a volcano or slowly overflow in the form of lava flows. Eruptions are usually composed of volcanic ash and are rich in chemicals such as potassium and argon, and the rock formed by volcanic ash is tuff.
Tuff has a unique chemical form and is therefore an important reference factor for dating paleoanthropological sites.
03
In fact, paleoanthropologists do not directly measure the age of human bone fossils, because this is inaccurate. Generally speaking, the carbon-14 method, also known as the radiocarbon dating method, is a commonly used technical means. However, this method is less used in the field of paleoanthropological fossil research. The main reason is that the carbon 14 dating method can only measure tens of thousands of years at most, and the formation time of human bone fossils is much greater than the limit of this method.
In fact, most of the time, paleoanthropologists will directly refer to the stratigraphic dating method in geology, which can easily solve the problem of human bone fossil ageing.
According to the basic laws of geology. In the sequence of layered rock formations, the first formed layer is located below, and the later formed rock layer is located above. According to the superposition relationship between the position of the rock layer, the formation time of the formation of the formation can be roughly determined.
The time of the rock formation is determined on the basis that if some paleontological fossil combinations are found in a certain rock formation, the age of the rock formation can be determined.
In addition to the paleontological fossil dating method, it is also possible to measure the age of rock formations using the isotopic method (not the C14 method).
When it comes to isotopes, it actually refers to the same element with the same number of protons and different neutron numbers. For example, carbon-12, carbon-14, or uranium-235, uranium-238 and so on.
Taking carbon atoms as an example, it can contain 6 or 8 neutrons, which corresponds to carbon-12 and carbon-14.
Carbon-12 is very stable, and carbon-14 loses neutrons at a fixed rate (5730) and decays into nitrogen-14 until it stabilizes, a process called decay.
The decay process is completely unaffected by the outside world, and this characteristic is very suitable for measuring the time of rocks. Thus a variety of isotopic dating methods were born.
The isotope measurement time span is very large, often hundreds of millions of years using uranium-lead dating, uranium-238 decay to lead-206 half-life is 4.47 billion years. Slightly shorter, potassium argon dating is used, and the decay of potassium-40 to argon-40 has a half-life of 1.3 billion years.
Usually, when scientists measure the dating of volcanic rocks, the potassium argon dating method is more commonly used.
This is because when the volcano erupts, the magma contains a certain amount of potassium-40, and the boiling point of argon is particularly low, and it will completely volatilize at high temperatures.
That is, the cooled rock is initially argon-free, but as potassium-40 decays into argon-40, these argon-40s are actually trapped in the rock, so just knowing the ratio of potassium-40 and argon-40 in the rock can calculate the age of the volcanic rock.
04
8 million years ago, much of Africa was covered with dense forests, dotted with rivers and lakes, and most primates lived in trees, where the common ancestors of humans and chimpanzees were. For the next 3 million years, the Earth experienced a long period of cold climate.
As the climate gets colder and drier, Africa's dense forests are gradually replaced by open woodlands, and grasslands appear between them. It was during this period of climate change that human ancestors began their evolution in Africa.
Bipedal upright walking is an important feature of the differentiation between humans and chimpanzees.
Dhikika region of Ethiopia
On December 10, 2000, in a remote area of East Africa, Ethiopia, In Dikika, a team led by Zerasena Alem Sergid of the American Institute of Human Origins discovered a skeleton fossil of Australopithecus (Alpha species), 4 kilometers away from the fossil of Lushin ape, known as the "mother of mankind".
A 3.2 million-year-old human fossil, Australopithecus Alpha species – Lucy
Through the dating of the tuff around the fossils, and according to the relative position of the fossils between the two layers of tuff, it is calculated that this Australopithecus lived between 3.31 million and 3.35 million years ago, more than 100,000 years before Lucy, which is the earliest human ancestor fossil found so far.
After a comparison of the fossilized crown of permanent teeth, the human bone fossil belonged to a 3-year-old girl, including a complete skull, a whole trunk bone, and incomplete limb bones, many of which still maintained their original connections and did not spread out. Such complete human ancestor fossils are rare, and children's fossils are even rarer, because children's bones are much more fragile and difficult to preserve.
The child was named "Selam," which means "peace" in the Ethiopian language, in the hope that several African tribes at war in the Afar region would move towards peace.
At that time, most of Seram's was buried in sandstone (sedimentary rock), and only a part of the small face was exposed to the ground, but these paleoanthropologists could see at a glance that it was a human fossil because of its smooth brow bone and small canine teeth. It is very different from the skull of an orangutan.
Removing fossils from rocks is very difficult, and care must be taken to remove the concrete-like stone around the fossils bit by bit with dentist tools.
2.5 million years ago Australopithecus African species - Towne toddler
Although Serram was only 3 years old at the time of her death, she already possessed the characteristics of Afa Southern Ape, such as her protruding nose and mouth, and narrow nose bone, which was very different from the 2.5 million-year-old Australopithecus African australopithecus (Australopithecus African species) - "Towne Toddler", unearthed in South Africa. And her jaw is very similar to Lucy the Australopithecus.
Most of Selam's skull was not found, but a rock model naturally formed in her cranial cavity had imprints on the inner wall of her skull, and from this cranial cavity model it can be inferred that Serram's brain volume is slower than that of chimpanzees, which is also in line with human characteristics. Because Selam's brain volume is only 65% to 88% of that of adults, chimpanzees can reach more than 90% of adult individuals by the age of 3. More importantly, Serram's "moon-like groove" (a curved depression on the surface of her brain) shows that her cerebral cortex is more like a human's than a chimpanzee or gorillas.
Like other Arphalian apes, Serram has many features of her leg and foot bones that indicate that she can walk on the ground on two legs, and that her heel width is closer to that of humans.
But part of her upper body is associated with adapting to life on the tree, her phalanges are long and curved to facilitate grasping branches, and her shoulder blades resemble apes (facing upwards) rather than humans (facing sides).
However, the ratio of the back of the Salaam scapula to the attachment area of the vertebrae muscles is quite similar to that of humans. Humans have a larger area on the lower side, while apes have a larger upper side.
Like other Arphalian apes, Serram has legs that are suitable for walking and fingers for climbing. A real-life example of "mosaic evolution" (the phenomenon of uneven rates of evolution in different parts of an organism) shows that evolution cannot be like magic, turning a four-legged animal into a person who stands up straight and walks on two legs.
In natural selection, the evolutionary pattern of bipedal walking animals must be that the lower limbs and pelvis evolved first, and the upper limbs and shoulders gradually evolved later.
Therefore, scientists unanimously believe that australopithecus alpha species is the direct ancestor of the genus Man, and a total of 17 species of the genus Have been found, of which 16 species are extinct, and only our Homo sapiens is the "lucky one".
epilogue
Many people, though well-educated, still don't believe that humans evolved from apes and hope this article will help them.