What are the advantages of Homo

Our current human beings are members of the genus Homo. They evolved from Homo habilis through Homo erectus and early Homo sapiens. Why did only early members of the genus Homo develop into modern humans while the various Australopithecus species living at that time failed to continue developing and became extinct? What competitive advantage does Homo have? Before we talk about the specific process of the development of Homo, let us first understand the advantages of Homo.

1. A leap in brain capacity

All australopithecines have small brains, large cheek teeth, protruding upper and lower jaws, and implement an ape-like survival strategy. They ate mostly plant foods and probably had social relationships similar to those of modern baboons living in the savanna. They only walk like humans, but nothing else is the same as humans.

Compared with Australopithecus, the brain size of Homo habilis has developed dramatically; on the other hand, their teeth have also changed, showing adaptation to changes in food habits (eating more meat) . But that's not all. New research into the biology of our human ancestors shows that many other aspects of the genus Homo also changed, allowing the creature to jump from the ape-like end to the more human-like end.

2. Unique growth curve

One of the most important characteristics of modern humans is that babies are weak and helpless when they are first born from the mother's body. As they grow, they must go through a long period of childhood and then go through a growth spurt during adolescence, when their height increases at an alarming rate. Among existing mammals, humans are the only ones to exhibit this phenomenon; most mammals, including apes, move almost directly from infancy into adulthood. From a young individual to adulthood, the body size of modern humans increases by about 25% during adolescence, when growth suddenly accelerates. On the contrary, the growth curve of chimpanzees is very stable, and their body size only increases by 14% from youth to old age.

So why do modern humans show this unique growth curve? It turns out that this is related to the high-intensity learning process that humans must go through during their growth. If there is a big difference in body size between growing children and adults, children will be in awe of adults and establish a teacher-student relationship, which will help children learn from adults better; if human children follow the same rules as apes, The growth curve quickly brings the body to a height close to that of an adult, and it may lead to confrontation rather than awe of adults. After the relatively long and arduous learning period has passed, the human body can "catch up" with the accelerated growth spurt of adolescence.

The reason why modern humans need such a long period of intensive learning is because when they grow up, they not only need to learn survival skills, but also learn cultural aspects such as traditional family relationships and life rules. Culture is a special adaptation unique to humans in all the animal kingdom, made possible by unusual patterns of growth and development during childhood and maturity.

3. The weak and helpless infancy

However, the weakness and helplessness of modern human newborn babies is not a cultural adaptation, but a biological phenomenon: because humans have large brains but restrictive pelvic structures, human babies are born relatively early.

Brain size is not only related to intelligence, but also to important events in life history, such as age at weaning, age at sexual maturity, gestation, and lifespan. Infants of related larger-brained species are weaned later, reach sexual maturity later, have longer gestation periods, and have longer individual lifespans than smaller-brained animal species. A calculation based on comparison with other primates shows that if the brain volume of a newborn baby is to be proportional to the body, the gestation period of a modern human with an average brain volume of 1350 ml should be 21 months. Not the actual 9 months. That is to say, the brain capacity of a human baby is far from reaching the level it should be when he is born; to reach that level, he (she) still needs one year of development time to catch up; therefore, he (she) must be born with Is weak and helpless.

So why can’t modern humans give birth to babies with appropriate brain capacity and a certain degree of self-help after 21 months of pregnancy? Why does nature prematurely expose human newborns to the dangers of entering the human world? This is determined by the large brain and relatively small pelvic opening that humans have.

There is a common trend in the ontogeny of apes and humans, that is, brain development is faster than body development; that is, brain volume quickly reaches the level of adult individuals early in life history. The average brain volume of ape newborns is about 200 ml, which is about half of that of adults. Therefore, ape newborns can have a certain degree of self-help. If modern humans also give birth to newborns with a certain degree of self-help ability like apes, then the brain volume of the newborn should reach 675 ml. It is extremely difficult for human females (women) to give birth to a baby with such a large brain, and sometimes even threatens the mother's life. In the process of human evolution, the opening of the pelvis has increased to accommodate the enlargement of the baby's brain; however, the increase in the opening of the pelvis is limited, and it is restricted by the movement method of walking upright on two legs; when When the brain volume of a newborn is the current average of 385 ml (about 1/3 of an adult), the opening of the human pelvis has actually reached its limit.

From newborn to adulthood, human brain size increases twofold, while that of apes only doubles. This different pattern of brain development itself is an important aspect that distinguishes humans and apes.

On the other hand, let’s make a reasoning: Taking the average brain volume of human newborns as 385 ml, twice its size is 770 ml; then, if a certain higher primate exceeds this number when it reaches adulthood, it means that the brain volume is increasing during growth. It has to increase by more than 2 times, which means that the development pattern of babies entering the world weakly and helplessly "prematurely" has begun. Then their development type should be closer to humans and far away from apes. From this point of view, the adult brain volume of Homo habilis is about 800 ml, which seems to have just left the branch point between humans and apes and started in the direction of humans; while the brain volume of early Homo erectus is about 900 ml, indicating that they have obviously The earth is moving in the direction of mankind.

Tecana Boy

Alan Walker, an anatomist at Johns Hopkins University, speculated based on the fossil of Homo erectus "Tekana Boy" discovered by Richard Leakey's research team on the west shore of Lake Tekana in northern Kenya in 1984. The human pelvic opening is smaller than that of Homo sapiens, and the brain volume of a Homo erectus newborn is approximately 275 ml. This volume is much smaller than the brain of a modern human newborn; however, it is exactly 1/3 of the adult brain of Homo erectus, a ratio that is the same as that of modern humans. This means that Homo erectus babies were born as helpless as modern humans.

Because the pelvis of Homo habilis, the direct ancestor of Homo erectus, has not yet been found, scientists have not yet been able to make similar calculations for Homo habilis. If the babies of Homo habilis were born with brains as big as those of Homo erectus newborns, they would also be born "prematurely", but not as "seriously" as Homo erectus; they would also be weak and weak at birth. Helpful, but the duration of this state will be shorter than that of Homo erectus; they will also live in a social environment like humans, but their social environment is relatively simple and primitive. Therefore, it can be speculated that from the time when the genus Homo first appeared, it began to live, develop, and respond to the challenges of nature in a completely different way from the past. In contrast, although various Australopithecus have also stood up and moved their feet, they still have smaller brains similar to apes, so their early development still follows a similar pattern to apes. Type.

4. The extension of childhood

From the earliest days of the genus Homo, humans have needed the careful care of their parents during the long period of time when they were weak and helpless in their infancy. But what about the rest of childhood? How long does childhood need to last before human children can learn enough skills and culture, absorb enough practical experience, and successfully enter and survive the subsequent growth spurt of adolescence?

The prolongation of childhood in modern humans is due to slower physical growth compared with apes. Therefore, any milestone event experienced by humans in their life history comes later than that of apes. For example, the eruption time of the first permanent molar is about 6 years old in human children and about 3 years old in apes; the eruption time of the second permanent molar in humans is between 11 and 12 years old, while in apes it is 7 years old; the third permanent molar emerges at 18 to 19 years old for humans and 9 years old for apes.

In the late 1980s, anthropologist Holly Smith of the University of Michigan in the United States developed a method to deduce the life style of fossil humans by linking brain size with the age at which the first permanent molars erupted. She accumulated the materials of humans and apes as a baseline, and then compared them with fossil humans. As a result, she analyzed three life history types: 1. For modern humans, the first permanent molar erupts at the age of 6, and the average life span is 66 years; 2. Intermediate type; 3. In the ape type, the first permanent molar erupts when it is slightly older than 3 years old, and the average lifespan is about 40 years. In this analysis system, all Australopithecus belong to the ape type; late Homo erectus, that is, Homo erectus who lived later than about 800,000 years ago, is a modern human type like Neanderthals; Early Homo erectus belongs to the intermediate type. For example, the first permanent molar of the Tecana boy (early Homo erectus who lived 1.6 million years ago) may have erupted when he was slightly older than 4 and a half years old. If he did not erupt at the age of 9 Dying young, he could have expected to live to about 52 years of age.

The conclusions reached by Smith's analysis aroused fierce debate at the time, because the traditional view was that all members of the family, including Australopithecus, followed a human-like pattern of slow early development. How to prove who is right and who is wrong? As it happens, anatomists Christopher Dean and Tim Bromage at University College London have just devised a way to directly determine the age of teeth: when viewed under a microscope, there are lines on the teeth that look like tree rings. can reflect their age. Dean and Bromage applied their techniques to the field of paleoanthropology, studying an Australopithecus mandible. In terms of dental development, this mandible is comparable to that of a Taung child, with the first permanent molars erupting on it. The lines on the teeth indicate that the individual died shortly after the age of three; the observations indicate that the growth curve of Australopithecus followed an ape-like pattern.

Dean and Bromage observed other types of human tooth fossils and found the same three types as Smith's conclusion: modern human type, intermediate type and ape-like type. Among them, Australopithecus is the ape type, early erectus is the intermediate type, and late erectus and Neanderthals are the modern human type.

These research results have once again caused controversy. It was not until anthropologist Glenn Conroy and clinical scientist Michael Vanier of Washington University in St. Louis brought high technology from the medical community to the anthropology laboratory that this debate was finally settled. They used computerized three-dimensional CT scanning technology to see the inside of the fossilized mandible of the Taung child. The results basically confirmed Dean and Bromage's conclusion that the Taung child died when he was about 3 years old. He was an ape-like person. Growth curve patterns in young children.

New technologies such as studying important events in life history through fossils and inferring biological characteristics by studying tooth development have brought paleoanthropology to a new level. Using these techniques we can surmise that the Tecana boy will be weaned before the age of 4; if he survives, he will reach sexual maturity at about 14 years old; his mother may have her first child at 13 years old .

5. Important changes in social structure

The evolution of the growth and development patterns of early members of the genus Homo toward modern humans occurred under a series of certain social conditions. All primates are social, but the social behavior of modern humansThe ability has been developed to the highest degree. Biological changes inferred from the dental evidence of early members of the genus Homo tell us that their social interactions had begun to intensify, that they had created a social environment that cultivated culture; and that the overall social structure had also undergone important changes. This change can be clearly seen by comparing the proportions of male and female bodies and contrasting such proportions with what we know about various primates.

baboon

The population of baboons living in the savanna is sexually intersex, with males weighing twice as much as females. This sexual hermaphroditism only occurs when there is fierce competition among adult males for the opportunity to mate with females. Like most primates, male baboons leave their original group when they reach adulthood and join another nearby group. From then on, they are in competition with other male baboons that have settled in that group. This way of male migration means that most males in a baboon group are usually not related, so there is no Darwinian reason (i.e. genetic reason) for them to cooperate with each other because they share certain genes.

Chimpanzee

In chimpanzee populations, by contrast, males remain in their natal group while females migrate to other groups. As a result, males in the same group are brothers to each other and share half of their genes. Therefore, there is a Darwinian reason for them to cooperate with each other in obtaining females. They cooperate against other groups of chimpanzees; during occasional forays, they often cooperate with each other to corner a monkey into a tree and capture it. This lack of competition and increased cooperation between males is reflected in the proportions of male and female bodies that are different from sexual hermaphrodites. At this time, males are only 15% to 20% larger than females.

In terms of the ratio of male to female body size, all kinds of Australopithecus are consistent with the shape of baboons. It is therefore reasonable to speculate that the social life of Australopithecus was similar to that of modern baboons. Judging from the situation of Peking Man, the typical representative of Homo erectus, the difference in stature between men and women in Homo erectus is smaller than that of Australopithecus, but larger than that of modern humans. When comparing the situation of early Homo sapiens, we find that men are only 20% larger than women. Anthropologists Robert Foley and Phyllis Lee of the University of Cambridge believe that such changes in male and female body proportions must reflect changes in social structure when the genus Homo originated. Men in the early genus Homo likely stayed with their brothers from the same father or mother in the group in which they were born, while the women migrated to other groups; this method must have promoted competition among the men. cooperate.

So, what is the reason that prompted such changes in the social structure? Some anthropologists believe that close cooperation between males helps protect them from aggression from neighboring groups. But more evidence suggests that this change is more likely due to changes in Homo's dietary habits - meat became an important source of energy and protein. Hunting to obtain large amounts of meat necessarily requires greater cooperation among men in the same group.

6. Increased carnivorousness

Signs of increased carnivory in Homo are reflected in all aspects of its morphology and physiology.

The structure of the teeth and upper and lower jaws of early Homo was different from that of Australopithecus, showing a stronger carnivorous habit.

The increase in brain size of early Homo also indicates the enhancement of its carnivorous nature. Biologists have proven that the brain is an organ that consumes a lot of energy in animal metabolism. Taking modern humans as an example, the brain only accounts for 2% of the body weight, but consumes 20% of the total metabolism of the human body. Primates are the animal group with the largest brains, and human brains greatly exceed the level of ordinary primates. If the weight is the same, the human brain is three times that of an ape. Therefore, the increase in brain size in early Homo must be related to the acquisition of higher energy. In other words, early Homo's food had to be both responsibly sourced and nutritious. Such food resources can only be meat, because only meat is the most efficient concentrated source of calories, protein and fat. All this suggests that early Homo could develop a brain larger than that of Australopithecus only if it greatly increased the proportion of meat in its diet.

7. Have stronger adaptability in exercise methods

In addition to teeth, jaws and brain size, early Homo also showed stronger adaptability than Australopithecus in other aspects of physical fitness. These physical characteristics illustrate that although Australopithecus can walk on two legs, it is not flexible Sexual performance was still poor; early Homo was agile and began to run efficiently.

This conclusion first came from the study of Lucy by anthropologist Peter Schmid of the Institute of Anthropology in Zurich. He used a fiberglass model of fossil bones to assemble Lucy's full-body skeleton and found that her thorax was cone-shaped, like an ape's, rather than barrel-shaped like a human's; moreover, Lucy's shoulders, torso, and waist were also very similar. Ape shape. So, Schmid explains, the species of Australopithecus afarensis represented by Lucy was not able to lift its chest to take the deep breaths we take when we run. Moreover, they have pot bellies and no waists, which limits flexibility; flexibility is very important when humans run.

Leslie Aiello, on the other hand, measured the length and weight of modern humans and modern apes and compared them with those of fossil humans. In contrast to modern apes, which are stocky and weigh twice as much as humans of the same height, Australopithecus was ape-like, and all members of the genus Homo were as light and agile as modern humans.

Recalling the original adaptive significance of bipedalism, we remember that it arose as a more efficient way of moving in a changed natural environment. It allows bipedal apes to continue to survive and develop in habitats that are not suitable for ordinary apes. As bipedal apes search for a wide range of food resources in open, sparse forest areas, they are able to travel across larger geographical areas. When the genus Homo evolved, a new way of moving emerged - still walking upright on two legs, but much more agile and flexible. The flexible and light body allowed early hominins to walk or even run with "striding strides"; at the same time, they were also able to effectively dissipate the heat generated by such strenuous exercise. This was especially important for people living in the hot savanna areas of Africa. This was especially important for early members of the genus Homo. Efficient, long-striding bipedalism represents a core change in human adaptation. This change is also closely related to the transformation of human feeding habits, because it is conducive to active hunting behavior.

An active animal's ability to dissipate heat is particularly important to the physiological activity of its brain. Anatomical studies conducted in the 1980s by Dean Falk, an anthropologist at the State University of New York, confirmed that the structure of brain blood vessels in Homo showed that the blood flowing out of them could effectively cool the brain, while the situation in Australopithecus was very different.

Stronger support for the idea that Homo had greater adaptability in movement patterns comes from the anatomy of the inner ear of early humans using computed tomography. All mammals have three C-shaped tubes in their inner ears called semicircular canals. The three semicircular canals are perpendicular to each other, and two of them are perpendicular to the ground. This structure of the semicircular canals plays a role in maintaining body balance. Fred Spurr, a scientist at the University of Liverpool, discovered that humans have two semicircular canals perpendicular to the ground that are much larger than those of apes. This phenomenon is obviously a special need for an upright posture in a bipedal species (human). Special adaptations for balance. Spoor continued to look at early human fossils, and the results were indeed surprising: in all species of the genus Homo, the anatomy of the inner ear was indistinguishable from that of modern humans; and in all species of Australopithecus, the semicircular canals were structured like apes. !

broken stone tools

8. Able to make tools

In summary, it can be seen that compared with Australopithecus, the physical superiority of Homo is self-evident. Let's turn to the clearest evidence of our ancestors' behavior - the most primitive tools made of stone.

2.5 million years ago, humans began to hit one stone against another to make sharp-edged tools (called stone tools), thus initiating a technological development process in which humans actively adapted to nature, utilized nature, and even transformed nature.

The earliest stone tools were small stone flakes made by hitting one stone against another. They were about 2.5 centimeters long and had surprisingly sharp edges. Although this stone chip is simple, it has many uses. Archaeologists Lawrence Keeley of the University of Illinois and Nicholas Toth of Indiana University discovered different scratch marks on the stone flakes under a microscope. Some scratches are caused by cutting meat, some are caused by cutting down trees, and some are caused by cutting softer plants such as grass. Therefore, it is conceivable that our ancestors once came to a simple camp by the river, cut down saplings with some stone flakes to build a frame, and used other stone flakes to cut thatch and cover it on the top of the frame to create a simple building. Under the shelter of this simple building, they slaughtered their prey with other pieces of stone, and began their primitive life that has led to today step by step.

The earliest stone tool assemblage discovered so far dates to about 2.5 million years ago, and in addition to stone flakes, it also includes larger tools, such as choppers, scrapers and various polygonal tools. In most cases, these stone artifacts were struck from a large block of stone. Mary Leakey spent many years studying this earliest technology in Olduvai Canyon, hence the name Olduvai Industries. This set of technology lasted until about 1.4 million years ago. Its basic feature is that it is whatever it is produced, and there are no rules to follow.

However, this kind of technology, which has no rules to follow and works as it is produced, has ushered in a new era in the history of human evolution. When our ancestors discovered the secret to consistently making sharp stone flakes, they suddenly had access to food that was previously unavailable. Small stone chips are an efficient tool. They can cut through animal skins that would have been impossible for people in the past to bite through with their teeth, thus exposing the animal flesh. As a result, people who make and use these simple stone flakes can obtain a new energy source-high-quality animal protein. As a result, they not only expanded the scope of their foraging, but also, on the one hand, this new high-efficiency energy provided nutritional support for their increased brain size, and on the other hand, it also increased the chance of successfully producing offspring. The reproductive process is a process that consumes a lot of energy. Expanding the diet, especially increasing meat, will make the reproductive process more secure.

The age of Olduvai industry is when the earliest members of the genus Homo existed at the same time as many species of Australopithecus, so who made these tools? The most reliable conclusion is that of the genus Homo. On the one hand, the genus Homo has a more developed intelligence (large brain) that can make tools; on the other hand, various Australopithecus have obviously different specific adaptations from those of the genus Homo, and the meat-eating of the genus Homo is likely to be the reason for this An important part of the difference - for early humans who did not have the sharp claws and teeth of carnivores, stone tool making was an important part of the ability to eat meat. Without these tools, plant eaters could survive.

When Toth studied tools from archaeological sites in Kenya and conducted tool-making experiments, he found that among the earliest toolmakers, more people used their right hands than their left hands, just like modern humans. This right-handedness corresponds to a brain asymmetry that is absent in modern apes. This means that the brain of the genus Homo became a "real human brain" as early as about 2 million years ago.

All in all, Homo's adaptation was successful, and weEverything humans have achieved today is evidence of this.

9. Why are there only people...?

But why haven’t other bipedal species survived to this day as companions to humans?

Starting from 2.5 million years ago, the genus Homo coexisted with several species of Australopithecus in East and South Africa. However, by 1 million years ago, all Australopithecus species went extinct one after another. How did this fate happen?

It is undeniable that the development of the genus Homo itself is the main reason for this ending. The number of early Homo is likely to increase rapidly, thus becoming the main competitor with Australopithecus for food resources for survival (although Homo has increased its meat diet, it still consumes a large amount of plant food); by now About 2 million years ago, when Homo erectus appeared, this competition became even more favorable to the genus Homo, because Homo erectus was an extremely successful species and they left Africa for the first time in the history of human evolution. In addition, between 1 million and 2 million years ago, baboons, a species in the superfamily Macaques that lived on the ground, also evolved very successfully, their numbers increased, and they will continue to compete with Australopithecus apes. Australopithecus probably became extinct under the dual competitive pressure exerted by Homo on the one hand and baboons on the other.

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