In the deserts of Central Africa, the oldest known fossils of humans have been found.
It complicates the history of human evolution.
The wind carried the sand and blew endlessly. This desolate desert, located on the southern edge of the Sahara, is 2,500 kilometers away from the Great Rift Valley, which paleontologists are most enthusiastic about, and the environment is very different.
The fossil layer is only a few meters thick at most, far from the sedimentary beach, and difficult to detect. Michel Bryne of the University of Poitiers in France and his companions excavated tirelessly in the Dracula Desert in northern Chad. In paleoanthropology, Central Africa did not have a reputation for miracles before, but a skull can change that — and it also changes humanity's understanding of its own history, just as it did 77 years ago in the Australopithecus African fossil.
In 1925, Raymond Dart reported in the journal Nature that he had found the skull of a juvenile primate in a limestone mine in the Towne region of South Africa, a mixture of ape and human features. Dart believed that this "Towne toddler" fossil was a "missing ring" between apes and humans, and named it australopithecus African species.
Until then, knowledge of one's distant ancestors was limited to a few ancients who possessed full human characteristics—Neanderthals, Javan apes (Homo erectus), and Pertang (this was later found to be false). Although the status of evolution has been established, many people are not ready to accept a half-ape, half-human ancestor, nor are they willing to believe that human roots are not in Eurasia but in Africa. So the authorities said that what Dart found was only the skull of a monkey.
But Dart was finally proven right, and "Toddler" ushered in a new era of paleoanthropology. Later researchers, such as Robert Bloom and the Leakey family, dug up many famous bones in eastern and southern Africa. These ancestors crowded between 5 million and 2 million years ago, constantly bringing new clues and new puzzles to those trying to reconstruct the human evolutionary tree. Nature — still Nature — publishes the story of a newly discovered fossil, Tomai, in Chad. The lesser-known scientists, in the underappreciated fossil region, found a skull of great significance, which looked like The story of Dart was repeating itself. However, Bruynei's luck was better than That of Dart, and he didn't have to wait many years to get cheers from his peers.
It was suggested 150 years ago that humans are particularly closely related to chimpanzees than other primates.
Archaeological evidence and DNA analysis support this view. In recent years, we have also known that the genetic difference between humans and chimpanzees is only a little more than 1%. It is estimated that the distant ancestors shared by humans and chimpanzees lived 7 million to 5 million years ago. Darwin's belief that humans are deeply rooted in Africa, and that the ancient human fossils found outside Africa so far have not exceeded the 2 million-year-old limit shows that this view is more reliable. Roughly speaking, the independent evolution of the genus human beings began on the African land 5 million to 3 million years ago.
People are peeking into their own path from the four "windows" of Africa. The oldest window is South Africa, where the Australopithecus African species originate. The largest and busiest window is the Eastern Branch of the Great Rift Valley, stretching from northern Ethiopia near the Gulf of Aden in the north to northern Tanzania in the south, passing through Kenya in the middle. The other two windows, Malawi and Chad, produce a limited number of fossils and therefore do not resemble windows in comparison to two peepholes. The oldest human fossils found before Thomas, unearthed in Ethiopia and Kenya, are both newly reported. The East Of the Great Rift Valley has soiled so many and ancient fossils of primitive humans that some scientists believe that the Rift Valley served as a geographical isolation. The arid, open environment to the east of the Rift Valley forced the apes to walk down the trees and develop into humans; in the wet, densely forested west, the apes still lived in the trees. This claim is known as the "Story of the East Side". However, in 1995, Burine excavated a fossil of a more than 3 million-year-old jaw in Chad, which was identified as a australopithecus species, named australopithecus Gazare, which wrote a beginning for the "story of the west"; the excavation of Tomai made a heavy mark on the west.
Despite the harsh environment of the Dechara Desert, many of the vertebrate fossils are well preserved, and Tomai, the fossil numbered TM266-01-060-1, is unexpectedly intact. It contains a skull, jaw fragments and several teeth, unearthed in the desert in a place in the tolos Manara region designated TM266. Since no dust layer provides the required argon and potassium, there is no way to age formations with their isotopes. Magnetic dating also does not apply here. However, the TM266 region is rich in a variety of vertebrate fossils, and comparing them with similar fossils found in East Africa can indirectly determine the age of TM266 by the stratigraphic age of East Africa. The fossils best correspond to TM266 in two regions of Kenya, providing reliable inferences: 7 million to 6 million years ago.
This is a very critical time. 10 million years ago, the world was full of apes.
About 5 million years ago, the genus was already full of wings. We know almost nothing about the critical phase of the separation of humans and chimpanzees — all the fossils previously found belonging to this period are enough to fill a shoe box. You can imagine how excited and nervous Tomay would have made paleoanthropologists, not to mention how strange it looked. Simply put, it looks like a chimpanzee from the back and like a Australopithecus 1.75 million years ago. Its skull resembles that of an ape, but on closer inspection it has many features: smaller canine teeth, thicker enamel of teeth, prominent eyebrow ridge shapes peculiar to humans, and characteristics of the junction of the back of the skull with the neck muscles indicate that he or she is walking upright. From the brow ridge, scientists tend to think of Tomei as a "he."
Tomei's taxonomic official name is the "Chadian species of Sahel" (the Sahel is a region south of the Sahara Desert that has been heavily desertified in recent decades). The nickname comes from the local vernacular and means "a child born during a dangerous period when the dry season is about to begin." If it's not at the starting point of the human evolutionary tree, it should be fairly close. But this is not to say that Tomei can simply be considered a direct ancestor of modern man. For a long time, scientists thought that human evolution was cascading, that is, taxonomically unique hominids appeared only once, and then continued to develop into higher forms. The members of each period have a little more human characteristics and less ape characteristics than the previous period, and finally become Homo sapiens. This model is neat and clean, and it is easy to draw on textbooks, which is really beautiful. But the facts are not so neat for our analysis and understanding. More and more new bones were being discovered, and the evolutionary tree was also full of ideas, becoming like a troublesome bush.
Some scientists have proposed that the early evolution of humans went through a process of "adaptive radiation": a species produced multiple different offspring branches, each adapting to the new environment in its own way, taking a different evolutionary path. In the process, some important human traits such as upright walking, dexterous hands, and enlarged brains may have evolved along different paths many times. The human evolutionary tree may have multiple beginnings, and a few human traits alone are not enough to directly associate a single hominid with modern humans—Tomei may be our immediate ancestor, but it may not be, and there is no hope of proof.
All that is certain is that Tomei supports the messy bush-like model of human evolutionary history, and causes big trouble for the cascade model: such an ancient hominid, who should have only just begun to show a little trace of humanity, should not look so much like a Australopithecus whose geological age is only one-third of its age.
If a cascade model were to be used to house Tomai, all the fossils that appeared later and whose faces were older than it—and the list is long—would all be expelled from the human family. For the sake of simplicity, it is better to think that Tomei was just one of the many new kinds of primitive humans that emerged in that era of major change, the tip of an iceberg sunk in distant history. More contemporaneous fossils undoubtedly help us understand that period, but unfortunately our ancestors and ancestors' relatives were not very cooperative: the forest environment they preferred was not conducive to fossil remains, such as the fossils we never found chimpanzees.