The second assignment for *Animal Biology* took me a full two days and more, the greater part of which was spent fruitlessly searching Chinese Academic Journals for reference papers. In the end I once again discovered that nine out of ten papers written by Chinese people are garbage; books are still useful. And among books, only those written by foreigners are useful. Although the bibliography includes two Chinese books, one a textbook and the other one I bought specially, both clearly plagiarize whole passages from Richard Leakey’s *The Origin of Humankind*. But does saying that a book is “compiled” rather than “authored” mean one can omit notes? Even if “compiled” means that copying whole passages is allowed, those passages should still be annotated in full! Of course, my own article is 99% copied or paraphrased and contains nothing original at all, but at least everything that should be footnoted has been footnoted, so I can face my conscience without guilt……
An Overview of Theories on Human Origins
Abstract: This paper briefly organizes the theories related to human origins.
Keywords: human origins; bipedal walking
Main text:
In the modern natural classification system, humans belong to the class Mammalia, the order Primates, the superfamily Hominoidea, the family Hominidae, the genus Homo, and the species sapiens. Homo sapiens is the only extant species in the family Hominidae, but human evolution did not proceed monotonically and stepwise toward a single goal; rather, it had countless branches and exploratory trials, and modern humans are the sole remaining branch-twig in the history of human evolution.
In examining the origins of humanity, one must first take note of this: what exactly is “human”?
This is an ancient question, and countless philosophers and scientists have asked it in different ways. The narrowest answer is, of course: the concept of “human” can only refer to modern people who possess a rich cultural, technical, linguistic, and spiritual world. But this is by no means a fair or precise definition; people once used behavioral traits such as “making and using tools” or ways of life as the definition of “human,” but because it was discovered that animals such as chimpanzees also make tools to some extent, and because of the defects of this definition in terms of clarity and operability, this criterion as a mark of humanity was gradually abandoned, although the ability to make tools remains one of the important standards for evaluating the level of human development.
The definition laid down by Plato more than two thousand years ago still seems the most succinct: “Man is a featherless biped.” Although this definition was mocked even then—Diogenes brought a plucked rooster into the lecture hall. But “walking upright” is indeed the most crucial point when modern biology defines the concept of “human.” For example, paleoanthropologist Richard Leakey stated plainly: “‘Man,’ in the most basic sense, simply refers to the ability to walk upright” ([1], p4). In order to exclude roosters and penguins, the additional condition of “featherless” also seems not to be dispensable; of course, a more precise way would be to make membership in the order Primates the defining condition.
Although biologists hold divergent views on the details of the course of human evolution, it is still possible to divide human evolutionary history, with some confidence, into four key stages: “The first stage is the origin of the human system (the family Hominidae) itself; that is, roughly 7 million years ago, ape-like animals changed into bipedal, upright-walking animals. The second stage is the proliferation of this bipedal species, a process biologists call adaptive radiation. Between 7 million and 2 million years ago, bipedal apes evolved into different species, each adapted to slightly different ecological environments. Among these proliferating human species, between 3 million and 2 million years ago, one species with a significantly larger brain developed. The enlargement of the brain marks the third stage and signals the emergence of the genus Homo; this branch of humanity later developed into Homo erectus and ultimately into Homo sapiens. The fourth stage is the origin of modern humans, the evolution of people like us, with language, consciousness, artistic imagination, and technological innovations unseen elsewhere in nature.” ([1], p5; [3], p343)
Therefore, research on human origins can broadly include questions concerning the above stages: first, the origin of the family Hominidae and its adaptive changes; second, the origin of the genus Homo; and finally, the origin of modern humans. But if upright walking is taken as the marker of human origins, then the focus of discussion should be the origin of the “family Hominidae,” and this paper will briefly organize the theories concerning the origin of the family Hominidae.
Research on human origins relies mainly on evidence from fossils and molecular biology. The judgment that the earliest hominids appeared about 7 million years ago benefits from molecular biology: in the late 1960s, Allan Wilson and Vincent Sarich compared the degree of structural difference in a certain blood protein between modern humans and African apes, calculated the rate of mutation, and inferred that the common ancestor of humans, chimpanzees, and gorillas began to diverge about 5 million years ago. Current molecular evidence has revised this time to about 7 million years ago ([1], p7).
Existing fossil material roughly accords with the predictions of molecular biology. The “Sahelanthropus tchadensis” discovered in 2001 (nicknamed “Toumaï”) is currently the earliest fossil material discovered that is thought possibly to belong to the family Hominidae, and lived 7 million to 6 million years ago. However, because its age overlaps with the prediction of the aforementioned molecular-clock theory, its taxonomic status remains highly disputed. ([2], p173).
In addition, the “Orrorin tugenensis” discovered in Kenya in 2000 (nicknamed the “Millennium Man,” living about 6 million years ago), the “Ardipithecus ramidus” discovered in Ethiopia in 1993–1994, the “Ardipithecus kadabba” discovered in 2001, and the “Kenyanthropus platyops” discovered in 1998 are all fossils whose taxonomic status remains uncertain. ([2], pp173-176) If these fossils are indeed human ancestors, then the date of the ape-human split may have been earlier than 7 million years ago. ([3], p344)
The genus whose taxonomic status has achieved scholarly consensus is Australopithecus. In 1924, Raymond Dart discovered a skull in the Taung quarry in South Africa and named it “Australopithecus africanus” (nicknamed “Taung”). This skull, contrary to the earlier “discovery” of “Piltdown Man” (which was not exposed as a fraud until 1953, when it was shown to be assembled from a human skull and an ape jaw), exhibited “human jaws and ape brain.” Since at that time people tended to regard the development of the brain as the driving force of human evolution, “some even thought that our ancestors’ shift to walking on open grasslands was the product of the development of human intelligence, precisely because intellectual development led our ancestors to appreciate the benefits of leaving the forest” ([4], p408). Therefore, Piltdown Man better suited the assumptions of the scholarly world at the time, whereas Dart’s discovery was instead regarded as a “bizarre mistake”; “although the Taung Child caused a sensation for a time, most of the time it was treated as an object of ridicule in cartoons and a topic of mockery in music halls.” ([5], p187)
With the successive discovery of new fossil material and the exposure of the Piltdown Man hoax, the status of Australopithecus was recognized. The currently more certain species of Australopithecus are usually divided into two broad types: gracile and robust. The former includes afarensis, africanus, anamensis, and afarensis? actually no—湖畔种, 阿法种, 非洲种 and 惊奇种; the latter includes aethiopicus, robustus, and boisei.
Apart from the Taung Child, the most famous fossil among the australopithecines must be “Lucy.” In 1974, a joint French-American expedition led by Donald Johanson and Maurice Taieb discovered many fossil bones in the Hadar region of Ethiopia, including the largely complete skeleton of a female individual around 20 years old later named Lucy. Lucy’s body structure is extremely ape-like, with long arms and short legs. ([1], p24) She was about 1 meter tall and weighed about 27 kilograms, but the shape of her pelvis and femur indicates that she was already capable of walking upright. ([2], p181) Johanson concluded that Lucy was precisely the trunk of the human evolutionary tree, the ancestor of humankind, and he unhesitatingly named another set of fossils discovered afterward the “First Family.” ([5], p198)
But Lucy, and the genus Australopithecus as a whole, still occupies a controversial position in the human evolutionary tree. Richard Leakey clearly expressed skepticism toward Johanson’s discovery: “First, the size differences and anatomical variation among the Hadar fossils are overall too great to represent only one species; a much more reasonable view is that these bone fossils come from two species, perhaps more. … Second, this scheme makes no biological sense. If human origins go back 7 million years ago, or even only 5 million years ago, it is hard to accept that a species of 3 million years could be the ancestor of all later species; this is not a typical situation of adaptive radiation. Unless there are better reasons, we must think that the development of human history follows a typical pattern.” ([1], pp24-25) Leakey thought Johanson’s “Y-shaped” evolutionary tree was overly simplistic, and he also pointed out that describing the evolutionary lineage as a “bush” was more realistic than calling it a “tree.” ([5], p202)
Even two Swiss anthropologists suggested that Lucy was actually male: “he” was not a smaller-bodied female member of the species afarensis due to sexual characteristics, but very likely a fully built adult male ape of a different genus and species. One of the researchers, Martin Häsler, said: “I cannot be certain that Lucy must have been male. But I dare say that, judging from body size and sexual characteristics, Lucy probably should not be classified into the current genus and species.” ([5], p203)
In any case, at least some of Johanson’s conclusions were too hasty or dogmatic. For example, he forcibly assigned a series of fossils and footprints discovered by Mary Leakey (Richard Leakey’s mother) in Tanzania to the species afarensis; “In fact, research by the famous comparative anatomist Russell Tuttle of the University of Chicago shows that the foot bones excavated by Johanson in the Hadar region do not match at all the ape-man footprints discovered by Mary at Laetoli.” ([5], p204)
Although there is still controversy over whether Australopithecus was the direct ancestor of modern humans, “whatever their evolutionary status, these early humans show us that before the emergence of the advanced brain, humans already had millions of years of bipedal-walking history.” ([3], p344)
“Acquiring an upright posture was the first breakthrough in human evolution, but views remain controversial regarding the cause that drove this evolution.” ([4], p411)
Of course, what first comes to mind is that upright walking liberated the hands for making and using tools, but fossil evidence shows that upright walking began millions of years before tools were used (and no obvious signs of tool use have been found in most australopithecines), and australopithecine brains were also relatively primitive. Thus, although tool-making undoubtedly benefited from the liberation of the hands, in terms of origin the two are not directly related.
In addition, “the popular image of human origins often includes an ape-like animal leaving the woods and striding out onto open savanna, which is undoubtedly a dramatic image, but completely incorrect. Researchers from Harvard University and Yale University analyzed the soils of many areas in East Africa and proved that this image is wrong: Africa’s savannas, with their fauna undergoing large-scale migrations, are a scene that appeared only relatively late, long after the earliest human species emerged.” ([1], p12)
It is generally believed that the formation of the East African Rift Valley about 12 million years ago promoted the evolution of the hominids: “The existence of the Great Rift Valley produced two biological effects: first, it formed an insurmountable barrier hindering east-west movement among animal populations; second, it further promoted the development of a mosaic ecological environment.” ([1], p13) “Biologists have come to understand that this kind of mosaic environment, which provides many different kinds of habitats for survival, promotes evolutionary renewal. A population once widely and continuously distributed can be isolated and face new forces of natural selection; this is the secret of evolutionary change. Sometimes, if the environment changes suitably, change leads to extinction. Clearly, this was the fate of most African apes… But when most ape species suffered from environmental change, one of them fortunately acquired a new adaptation and was thus able to survive and flourish: this was the first bipedal ape. Clearly, under changing environmental conditions, bipedal walking was endowed with an important survival advantage, and the task of anthropologists is to discover those advantages. Anthropologists tend to think about the importance of bipedalism in human evolution from two aspects. One school emphasizes the liberation of the upper limbs so they can be used to carry things; another school focuses on the fact that bipedalism is a more energy-efficient mode of locomotion, while regarding the ability to carry things as merely an incidental by-product of the upright posture.” ([1], p14)
For example, Lovejoy proposed in 1981 that bipedal walking arose in order to carry things, so as to improve the efficiency of transporting offspring and carrying food. ([1], p14; [2], p191)
Peter Rodman and Henry McHenry proposed in the same year that bipedalism was an adaptive change to a new environment: “The earliest bipedal apes were human only in their mode of locomotion; their hands, upper and lower jaws, and teeth were still ape-like, because their food had not changed, only the way they obtained food had changed.” ([1], p15; [2], p190) They pointed out that although human walking efficiency is not as high as that of animals such as horses and dogs, it is indeed far higher than that of quadrupedal chimpanzees ([1], p15).
There are many other related hypotheses. For example, some people believe that bipedal walking enabled humans to evade attacks from other animals more easily, while others propose that upright walking reduced the amount of solar radiation received and therefore made it easier to dissipate excess body heat ([2], p191). Of course, it is difficult for all these hypotheses to find compelling evidence, so they can only remain conjectures.
In any case, upright walking made it possible for humans one day to learn complex tool techniques. On the other hand, the formation of human culture may also have been indirectly promoted by upright walking: the increase in infant brain size requires women to have a broad pelvis, but the needs of upright walking impose restrictions on this. “In order to accommodate these two needs, human evolution produced a series of complex adaptations. Although modern fetuses have large brain capacities, they are of the nurturing type, and only in adolescence do they undergo a compensatory sudden growth spurt.” ([2], p193) On this point, Barry Bogin proposed a special explanation: “If adolescents must receive cultural education, then the benefit of the growth spurt is related to the high-intensity learning they must accomplish. If the body size of growing children and adults differs greatly, then children can learn from adults more effectively, and a teacher-student relationship can be established. If the size of young children were to follow the ape-like growth curve to the height they could reach, then conflict rather than a teacher-student relationship might arise.” ([1], p35)
References:
[1] Richard Leakey: *The Origin of Humankind*, translated by Wu Rukang, Wu Xinzhi, and Lin Shenglong, Shanghai Scientific and Technical Publishers, 1995
[2] Li Fajun, ed.: *Biological Anthropology*, Zhongshan University Press, 2007
[3] Xu Chongren and Cheng Hong, eds.: *Animal Biology*, Higher Education Press, 1st edition, 2000; 2nd edition, 2008
[4] Peter Bowler: *The History of Evolutionary Thought*, translated by Tian Ming, Jiangxi Education Press, 1999
[5] Hal Hellman: *Great Feuds in Science: Ten of the Liveliest Disputes Ever*, translated by Zhao Lejing, Shanghai Scientific and Technical Publishers, 2000
Translated from the Chinese original with AI assistance. The original text is authoritative.
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