The earliest human beings
The direct evidence for studying the origin of human beings comes from fossils. Anthropologists use comparative anatomy to study all kinds of ancient ape fossils and human fossils, determine their relative and absolute ages, thus determine the age of human fossils, and roughly divide the evolutionary history of human beings into several stages. Geneticists, on the other hand, use the methods of biochemistry and molecular biology to study the differences and variation speed of protein and deoxyribonucleic acid (DNA) among modern humans, various apes and other higher primates, so as to calculate their respective origins and differentiation ages. At present, it is generally believed in academic circles that the time when apes became human ancestors was 7 million years ago.
Judging from the discovered human fossils, human evolution can be roughly divided into the following four stages:
(1) Australopithecus stage. The Australopithecus found lived from 4.4 million years ago to 6.5438+0 million years ago. According to the study on the anatomical characteristics of fossils, the most important feature of Australopithecus is that it can walk upright on both feet, which is different from apes.
(2) the stage of capable people. /kloc-fossils of homo habilis have been found in Tanzania and Kenya in East Africa since 0/960. The earliest possible life existed 6.5438+0.9 million years ago. An able person is classified as an able person below the human subject. Homo habilis has a bigger brain than Australopithecus, and can make tools (stone tools) from stones, and then gradually evolve into Homo erectus.
(3) Homo erectus. Homo erectus belongs to Homo erectus in classification, referred to as Homo erectus, commonly known as Homo erectus. Homo erectus fossils were first discovered in Java, Indonesia in 189 1. At that time, there was also a debate about whether people were apes or not. It was not until the 1920s that Peking man's fossils and stone tools were discovered in Zhoukoudian, Beijing, that Homo erectus was established in the history of human evolution. Homo erectus lived about 6.5438+0.7 million years ago to over 200,000 years ago. So far, homo erectus fossils have been found in Asia, Africa and Europe.
(4) Homo sapiens stage. Homo sapiens is generally divided into early homo sapiens (ancient homo sapiens) and late homo sapiens (modern man). Early Homo sapiens lived from 200,000 years ago to over 654.38 million years ago. The survival age of late Homo sapiens began about 654.38 million years ago. Its anatomical structure is basically similar to that of modern people, so it is also called modern people in anatomical structure.
According to the evidence of human fossils found so far, Australopithecus is the earliest known human.
Tang's skull
1924, in a place called Towne in azania, a small skull fossil was blasted by the quarry workers there. This fossil of Tony's skull was quickly sent to the Medical College of the University of Witwatersrand in Johannesburg and handed over to Raymond Dart, a professor of anatomy. Australian Dart has just returned from studying medicine, anatomy and anthropology in London, England. The skull fossils given to Dart by quarry workers, including most of the skull and a complete intracranial model, contain a full set of deciduous teeth and the first permanent molars that are erupting, belonging to young individuals (equivalent to modern children aged 3-6).
Dart found that this fossil has many characteristics of apes. For example, the brain of this young individual is about 500 ml like an adult gorilla, and it is estimated that it is only about 600 ml in adulthood. In addition, the upper and lower jaws protrude forward, similar to apes. At the same time, Dart noticed that this fossil also has human characteristics. Its teeth are very small, similar to human teeth. Most importantly, the foramen magnum, like humans, is located in the center of the skull base. The foramen magnum is the opening at the bottom of the skull, where the spinal cord connects with the brain. Because humans walk upright with their feet, their heads are balanced at the top of the spine, and the foramen magnum is located in the center of the skull base. The ape's head leans forward, and the foramen magnum is located behind the skull base. The characteristics of the foramen magnum in Tony's skull show that his individual can walk upright.
Based on these findings, Dart published a research report in 1925, pointing out that the individual to which this fossil belongs is a mixture of apes and apes, and it is an extinct ape that is closest to the human system found at present. Because it was found at the southernmost tip of Africa, the individual species to which Tang's skull belongs was named Australopithecus africanus. After the publication of Dart's article, it was ridiculed by many British authorities in anatomy and anthropology. They think this fossil is only an early ape fossil. In the following 10 years, this skull was rarely mentioned because of the discovery of Peking man fossils.
1936, another batch of fossils was blasted in the Fontaine quarry in stage, transvaal province. Among them, there is a complete skull that is very similar to Tony's skull. Since then, similar fossils have been found in Ryder, Macapansgate, Reims and Svatek, krom. By the 1950s, more than 70 Australopithecus fossils had been found in the above five sites. Academics classified Australopithecus fossils found in South Africa into two genera, namely Australopithecus africanus and Australopithecus robustus, or Australopithecus gracilis and Australopithecus robustus, and gradually established Australopithecus as the ancestor of early humans.
It should be pointed out here that Australopithecus is actually a member of the hominid family, although it is still called Australopithecus in name. According to the international nomenclature rules of paleontology, once a species is named, it cannot be changed at will. Therefore, the name of the ancient ape is still in use today.
Discovery in East Africa
In the late 1950s, the search for human fossils in Africa gradually moved to Ethiopia, Kenya and Tanzania in East Africa. The geological feature of East Africa is that there is a rift valley from south to north, and its surface is a series of canyons and lakes. There are a large number of volcanic sediments formed by volcanic eruption for millions of years in this area, which provide good materials for isotopic dating. Therefore, the age of fossils buried in these volcanic rocks can be accurately determined.
On July 1959 and 17, after 30 years of searching, paleoanthropologist Louis Leakey and his wife mary leakey finally found a nearly complete thick Australopithecus skull and a calf bone in the Odewe Canyon. The skull is particularly thick and there are huge molars on the gums. Mr. and Mrs. Li Ji named the species to which the skull belonged as Zinjanthropus boisei, and later changed it to Australopithecus boisei. In their view, Bauhinia is a robust species in East Africa. The common name Zinjanthropus means "people from East Africa", and the name boisei comes from Charles Boise. He once supported the work of the Leakey family in East Africa. The age of fossils is determined by potassium argon method, and it is determined that "East Africans" lived 6.5438+0.75 million years ago. In this excavation, stone tools and bone fragments of extinct animals were also found (it seems that they were fed on nutritious bone marrow). Can "East Africans" already make stone tools and even hunt animals? Judging from the skull, its brain is still too small to complete such complicated technical operations and labor. If these stone tools were not made by "East Africans", who made them?
1960, near the location where the skull of "East African" was found, Jonathan Leakey, the son of Louis Leakey, found a part of the skull and mandible of a child with the age of10 ~1,the hand bones of people of different ages, and the clavicle of an adult. 1963, another skull and mandible with the most teeth were found in the same place. The study of these fossils shows that this man is more progressive than the "East African". Its brain is almost 50% larger than that of "East African", its skull shape is more progressive, and its teeth are smaller than that of "East African", living 6,543,800+0,780 years ago. According to Dart's suggestion, Louis Leakey and others named it homo habilis as the first early member of Homa. The name "able person" means "handy person" or "skilled person".
Louis Leakey believed that the stone tools discovered during the excavation of "East Africans" were made by "homo habilis" and the bone fragments were also broken by "homo habilis". He believes that although Australopithecus is a part of the early ancestors of human beings, only "homo habilis" can continue to evolve to the later stage of human beings and eventually produce modern people. The discovery of "East Africans" and "able people" in East Africa is also the earliest evidence that two kinds of human family members live in the same area at the same time. Since then, many fossils of homo habilis have been found in Ethiopia and Kenya. The most important one is Richard Leakey, another son of Louis Leakey in 1972. His skull number is KNM-ER 1470, which was found on the east bank of Turkana Lake.
Since 1960s, a large number of Australopithecus fossils have been found in Omo Valley in Ethiopia and Hadar in Afa region, including hominid fossils from about 3.5 million to 6.5438+0.5 million years ago. Among them, two bones, the lower femur and the upper tibia, were found in Hadar, 1973, which have been proved to have the function of walking upright. These fossils can be traced back to 3.5 million years ago. 1974, Donald Johanson, an American paleoanthropologist, found most of the bones of a woman in the same area and named it "Lucy". According to the study of her pelvis, spine and kneecaps, it can be confirmed that she walked upright with two feet and lived 3.4 million years ago.
1976, Mary Leakey found a set of human footprints condensed in volcanic ash in Lettori area. This set of footprints left 3.7 million years ago is quite complete and its dating is quite reliable. According to the arch shape and gait analysis, it can be considered that it was left when walking upright. The above findings are the earliest evidence of human bipedal walking.
According to the comparative study of Hadar and Lettori fossils, Johansson and others think that the specimens of these two places are very similar, both of which walk completely upright with their feet and have small brains and big canine teeth, so they belong to a class and should be classified as a new species-Australopithecus afarensis. They think that some characteristics of Afa species are between apes and humans, but their ape-like characteristics are obviously changing to humans. Therefore, Afa is not only the ancestor of African Australopithecus, but also the ancestor of homo habilis. On the one hand, Afa species changed from australopithecus africanus to Robinia pseudoacacia species and eventually became extinct; On the other hand, it developed into homo habilis and homo sapiens.
By the early 1990s, there were five species of Australopithecus found in Africa, namely African species, Afa species, Robinia pseudoacacia species and Ethiopian species. These five species of Australopithecus are classified as the lanky and stout Australopithecus described above. African species and Afa species belong to slender type. Among them, Afa was earlier, represented by "Lucy"; African species are later, only found in South Africa. The other three species belong to the stout Australopithecus. The Ethiopian species was named after the mandible 2.5 million years ago. This fossil 1967 was found in southern Ethiopia. Many paleoanthropologists don't recognize this species and think it should be classified as Bowie species.
Since 1990s, there has been a new breakthrough in the study of early human fossils in East Africa. 1994, American paleoanthropologist Tim White and others announced that they had discovered a large number of ancient human fossils 4.4 million years ago in Afa basin, and named them Australopithecus ramidus. Ramid means "root" in Arabic, a local tribal language. Named after this fossil, it means that this is the oldest direct ancestor of mankind discovered so far. Later, Richard Leakey's wife, Maeve Leakey, and American paleoanthropologist Alan Walker discovered the Australopithecus Anamansis 4.2 million years ago on the west bank of Lake Turkana. Because there are still different views on the anthropological status of ancestor species in academic circles, it is generally believed that lakeside species is the earliest anthropological member who can walk upright.
Viewing human evolution from Australopithecus australis
Since Datt first discovered Australopithecus fossils in 1924, 7 species of Australopithecus fossils have been discovered so far. In the past few decades, the continuous discovery of new Australopithecus fossils and the multidisciplinary research on the discovered fossils have enabled the academic community to have a new understanding of the process involving the origin and evolution of early humans. Firstly, the position of Australopithecus in the whole human evolution system was established. In recent years, the discovery of Australopithecus fossils 4 million years ago has made the age of Australopithecus closer to the time of ape separation calculated by geneticists through DNA research; Secondly, the characteristics of various species in Australopithecus in fossil characteristics, survival age and evolutionary relationship with later hominids make anthropologists realize that the evolution process of human beings is much more complicated than originally thought. In the same time range, several Australopithecus species existed at the same time, but only one species evolved in the direction of hominid, and the rest eventually became extinct. This shows that human evolution is carried out in a "bush" way, not in a traditional linear way. This is of great significance to enrich the theory of biological evolution. The discovery and research of Australopithecus deepened human understanding of its origin and evolution, and promoted the development of paleoanthropology. It is worth mentioning that in the past decades, the niche family has made great contributions to the discovery and research of ancient humans in East Africa.
Old story in the east
Academics generally divide hominids into Australopithecus, Homo habilis, Homo erectus and Homo sapiens. Australopithecus is the earliest known hominid. So, what prompted Australopithecus to enlarge its brain, gradually acquire the ability to walk upright and make tools, and thus become human?
15 million years ago, Africa was covered with dense forests from west to east, inhabited by various primates, including many monkeys and apes. However, in the following millions of years, great changes have taken place in the environment there, leading to corresponding changes in biology. At that time, the crust under the eastern part of the African continent split along the Red Sea, passing through Ethiopia, Kenya and Tanzania today. As a result, the land in Ethiopia and Kenya rises like bubbles, forming highlands above 270 meters above sea level. These high bulges not only changed the landform of Africa, but also changed the climate of Africa. It destroyed the previous consistent airflow from west to east, making the east a less rainy area and losing the conditions for forest survival. The continuous forest began to break into patches of small forests, forming patches of forests, sparse forests and bushes. About 6.5438+0.2 million years ago, the continuous geological tectonic forces further changed the environment here, forming a long and narrow curved canyon from north to south. The existence of the Grand Canyon has caused two biological effects: first, it has formed obstacles to the communication between animals on the east and west sides of the Canyon; The second is to further promote the development of mosaic ecological environment. Some experts believe that this east-west barrier is extremely important for the branch evolution of humans and apes-dividing the ancestral groups of humans and apes into two parts. The group in the west of the Grand Canyon lived in a humid bush environment and eventually became modern African apes. In order to adapt to the life in the open environment, the ethnic groups in the east of the Grand Canyon developed a brand-new set of skills (walking upright on two feet, liberating upper limbs, and starting to use and make tools), which were transformed into human beings through Australopithecus. French paleoanthropologist Yves Coppens called this evolutionary model "the story of the East".
Africa or Asia?
Darwin put forward in 187 1 that Africa is the birthplace of mankind. His reason is that gorillas and chimpanzees, the two closest apes to humans, both live in Africa. At that time, early human fossils had not been found in Africa, and many people thought that an animist aristocrat like human beings could not have originated in the dark African continent. Therefore, Darwin's view is not generally accepted. But as mentioned earlier, since 1924, as many as seven species of Australopithecus fossils have been found in Africa. After years of debate, anthropologists agree that Australopithecus belongs to the human system. Its form is far more primitive than that of Asian ape-man (Homo erectus) and its age is earlier than that of the latter. Because fossils older than Australopithecus (such as Lamarck) are still uncertain in the system of human evolution, the current trend is negative, so Australopithecus is considered as the first stage of human development. Moreover, outside Africa, no fossils that must be Australopithecus have been found so far. Therefore, at present, most anthropologists believe that the origin of mankind should be in Africa.
From this perspective, the problem of human origin seems to have been solved. But in fact, the problem is far from simple, and the theory of African origin is not perfect. According to the existing evidence, including fossils, molecular biology and paleoecological data, it is generally estimated that human beings should have originated around 7 million years ago at the earliest. However, the earliest human fossils found in Africa were only 4.4 million years ago. Human fossils earlier than this era are only found sporadically, and the identification is still uncertain. In addition, there is no transitional type between Australopithecus and hominids in Africa so far. Therefore, it is not certain that Africa is the earliest place where human beings originated. In this way, some anthropologists are considering whether there are other possibilities.
As early as the late19th century, German scholar haeckel proposed that the similarity between Asian gibbons and orangutans was greater than that between African apes and humans. Therefore, human beings may have originated in Asia, especially in China. There are three reasons: first, the environmental and climate changes caused by the uplift of the Qinghai-Tibet Plateau are very similar to those in East Africa; Secondly, according to the study of ancient mammals, there were many similar animals in East Africa and East Asia in the past 10 million years, indicating that the ancient environment and climate of the two places were quite close; Thirdly, China has discovered a variety of ancient ape fossils, and unearthed a wealth of homo erectus and its later human fossils, as well as Paleolithic cultural relics. As to whether China is the birthplace of early humans, more fossil evidence and in-depth research are needed to solve this mystery.