Third, the essential reasons for the evolution of life
From the discussion in the previous section, we can see the charm of Darwin's theory of evolution, which gives a unified explanation for all the phenomena in the biological world: the consistency of biology can be explained by a common ancestor, and the diversity of species is entirely the result of evolutionary adaptation. Darwin's theory of natural selection may not account for the change from one species to another in today's world, but newly discovered knowledge and a growing body of paleontological evidence fully support Darwin's general theory of evolution. Darwin's theory of evolution, as a general description of the evolutionary process of life, also became more and more consolidated. But now there are some scientific people with ulterior motives who take advantage of some of the limitations of Darwinism to negate this and deny that, and finally want to inflate themselves through the value of great men. I don't think much of this practice. Professor Richard Dawkins of the University of Oxford, in his 1994 book The River of Eden, wrote: "In a sense, all the books I have written are devoted to expounding and exploring the infinitely powerful principles of Darwinian evolution. As long as there is enough time for the results of the original body and self to be reproduced, the power of Darwinism will be unleashed anytime and anywhere. "My article is also based on a general theory of evolution. Regarding the theory of evolution in a higher sense, due to the limitations of my knowledge, there is only a general discussion at the end, hoping to throw a brick and provide a little reference for biologists to study the theory of the evolution of life.
In the above discussion of the evolution of life, I would like to draw attention to a term - structure. As life evolves, so does the internal structure of life. From the earliest single-celled life evolved into forms with different and cooperative multicellular populations. These diverse and cooperative multicellular populations gradually differentiate into various cells such as heart, lungs, liver, skin, eyes, and brain. The result is a complexly structured organism composed of different organs, tissues and systems. Structure is becoming more and more complex in the process of life evolution, and the structure between different levels of life forms embodies the basic principle of evolution from low to high, from simple to complex, although there are still the simplest single-celled life structures such as marine plankton, but this just shows the role of environmental selection on the evolution of life. Because they can survive in that environment without evolution. This push is necessary for the evolution of life, but it is an external cause. Before discussing the essential reasons for the evolution of life, I would like to draw attention to another important concept — energy.
If we put aside the complex and diverse external forms of life and explore the development law of the internal structure of life, we will find that the only purpose of the development and evolution of the structure of life from simple to complex is to improve the efficiency of its own use of energy. In the process of the evolution of life, if a new species or a species obtains some kind of improvement that makes it more efficient in the use of material energy, it is possible to exclude an old species or unchanged species in the competition, resulting in the extinction of one side and the evolution of the other (see figure).
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Evolutionary improvements in the organs of predators ---> increase in the number of predators and the expansion of predator populations
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New evolutionary improvements ———————— —————— shrinking predator populations
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Extinction <---- Predator population shrinks <---- New evolution Extinction
—— Small, decreasing quantity Improvement ——
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The modern biological view suggests that the organism is an unbalanced, open, ordered dissipative structure. For organisms to maintain their order, they must constantly draw material and energy from the outside world in order to maintain themselves in a low state of entropy. Biological evolution theory holds that the order of the biological world is constantly improving, from simple to complex, from low to high, and evolves in a highly ordered direction. The increase in the ability to obtain effective energy will allow the organism to obtain more effective energy, thereby moving farther away from the equilibrium state and obtaining greater order. Therefore, the essential reason for the evolution of life is that organisms gain a higher ability to obtain effective energy through brutal competition for survival, thus standing out in natural selection and becoming the mainstream of evolution. In short, the essence of the evolution of life is to improve the internal structure of life and thus increase the efficiency of the use of energy. This can be demonstrated by the laws of development of any kind of internal structure of an organism, from simple to complex. Let's talk about the digestive system, the circulatory system and the nervous system.
As far as the digestive system of animals is concerned, protozoan amoeba only has to digest food bubbles, which surround food and digest it. To the grasshoppers develop simple feeding and digestion structures the mouth grooves and the anal points that excrete waste. Sponge animals have small holes and large holes in their bodies to let water flow in, but the channel in the center of the body has not yet developed into a true digestive tract, and food digestion is still in the form of amoebas.
Coelenterates such as the hydra, its mouth is both an eating and excreting mouth, and its coelenter is the most primitive digestive cavity. There are two types of cells in the lining of the coelum: one type of cell still uses amoeba and sponge to surround food with cells to digest it; the other type of cell differentiation has the nature of a digestive gland, which is a common way for all kinds of animals (including humans) to digest food than it. This way of digesting food is greatly improved in efficiency and directly promotes the evolution of life. This evolution is also due to the fact that organisms have evolved the ability to move freely and thus improve their ability to feed.
To the three germ layer of animals in the link animals such as earthworms, there are openings in the front and rear of the body, and the feeding mouth and the excretory anus are separated. The digestive system of the earthworm runs through the entire body, and there is no obvious distinction between the stomach and intestines in the digestive tract, it has a sandbag in front of it, and a long section behind the sandbag is both stomach and intestine.
The arthropod insects, which developed to the highest level in invertebrates, produced a variety of mouthparts, ranging from those suitable for biting and chewing to puncturing and sucking. The digestive tract of insects is still not easy to distinguish between the stomach and intestines, and a short section after the sandbag can be regarded as the stomach, and the latter section of the hind intestine can be regarded as the intestine.
Due to the appearance of bones, the ability of organisms to obtain food is greatly improved. More food directly requires improvement in the digestive system of vertebrates, and at this time, the digestive tract of vertebrates has obvious distinctions between the esophagus, stomach and intestines, and later the intestines are divided into small intestines and large intestines. The differentiation of the gastrointestinal tract makes the digestion of food more refined, and the efficiency of energy use in food by life is greatly improved, laying the foundation for promoting the development and evolution of other systems of the body. The lowest vertebrate round mouth does not have a jaw, and only fish have upper and lower jaws that can actively feed. Fish have small, sharp teeth in their mouths, and the structure is relatively primitive, which is used to bite food tightly, and then use auxiliary organs such as tongues to send food into the pharynx and swallow it. Later amphibians and reptiles had similar feeding patterns with tooth structures.
The digestive system of mammals has been fundamentally reformed, and their teeth are differentiated into incisors, canine teeth, premolars and molars, each with different functions, which can make food initially processed in the mouth first, which is convenient for gastrointestinal digestion and absorption. The gastrointestinal tract of mammals has also evolved. Become more advanced and complex. These evolutions have led to a great increase in the energy available to mammals in the same food, thus directly contributing to the evolution of other systems, especially the circulatory system, which in turn promotes the organism's ability to obtain effective energy, and is also the basis for the evolution of the nervous system.
The blood circulation system of animals also develops gradually with the evolution of animals, from scratch, from simple to complex. Lower animals, including protozoa, sponges, and coelenterates, do not have a circulatory system. It is only in the case of thymes and link animals, such as earthworms, that the tubular circulatory system appears. But it is not without a separate must be dirty, but several pairs of ring blood vessels in some of the body nodes that connect the back and the ventral surface of the two longitudinal blood vessels are particularly thick and elastic, which can help the delivery of blood, and these pairs of ring blood vessels can also be called the heart.
Only molluscs have separate hearts, distracting ventricles and auditory ears. The ventricles have a contractile force that pushes blood circulation. But its arteries and veins have not yet been directly connected, and the blood vessels are not completely enclosed in the blood vessels. Arterial blood flows into the blood sinuses of various parts of the body and then confluence into the veins, so it is called the open circulatory system. Arthropods and echinoderms are also open-tube circulatory systems, and in vertebrates, with the evolution of the digestive system, organisms have evolved a relatively complete closed-tube blood circulation system.
The hearts of both round-mouthed and fish are relatively simple, with only one atrium and one ventricle. The fish's heart is full of hypoxic blood. The ventricles send hypoxic blood to the gills for gas exchange, which becomes oxygenated blood, which is then sent to all parts of the body, and then becomes hypoxic blood flowing back to the heart. This blood circulation is called a single circulation.
Starting from amphibians, because oxygen in the air is easier to absorb than in water, on the basis of more efficient metabolism, animal blood circulation becomes a double cycle, that is, systemic circulation and pulmonary circulation, but amphibians and reptiles belong to incomplete double circulation. The ventricles are not completely separated, so the blood in the hearts of these two types of animals is still clear and mixed, and the metabolic rate is not high.
Mammals are true double circulation, the heart is divided into two atriums and two ventricles, oxygenated blood and hypoxic blood are no longer mixed. The complete double circulation makes the mammalian vertebrate body structure and function more perfect. The systemic circulation is responsible for transporting oxygen, nutrients and metabolic waste, and the pulmonary circulation is responsible for gas exchange, so that the blood supply oxygen is sufficient, creating conditions for maintaining a constant temperature and a strong metabolism. This progress is directly promoted by the evolution of the digestive system, and the differentiated teeth and the more advanced and complex gastrointestinal structure are the basis for ensuring that mammals get more energy, and also directly promote the evolution of the circulatory system. It can also be seen from this that the evolution of the various systems of the organism is not isolated, but complementary and mutually reinforcing. This also includes the evolution of the nervous system.
Let's take a look at the development and evolution of the nervous system. As mentioned above, its evolution is not isolated, but complementary to other systems, interacting with each other, and the fundamental reason for its evolution is the improvement of the ability of living organisms to obtain energy. In humans, the nervous system evolved the ability to think self-consciously, as a result of the revolutionary changes in food. The evolution of the nervous system after humans will still follow the basic principles of improved access to energy to promote evolution.
The origin of the nervous system is the stimulus sensing of living things, and all life forms have stimuli sensing. Even plants and the simplest protozoa have stimuli sensing, such as the feeding activity of amoebas, in which external stimuli act directly on any part of the organism (the cytoplasm) and cause an overall response, without differentiating into a special "feeling-response" mechanism or nervous system.
The so-called nervous system is a system used by the multicellular animal body to coordinate the reactions of various cells, so that the reactions of each cell will not occur chaotically. Such animals generally use the reflexive activity of the nervous system to express stimuli sensing. A certain neural route through which reflex activity is achieved is called a reflex arc. The reflex arc of higher animals has a special "feeling-response" mechanism, consisting of three parts: one is the receptor, including the receptor and the afferent nerve fibers associated with the central nervous system; the second is the central organ, that is, the central nervous system, including the brain and spinal cord; and the third is the reaction mechanism, including the different organs of the body together with the echient nerve fibers that innervate them. In such a reflex arc, the senses cause a variety of sensations, the muscles cause movement, and the afferent and efferent nerve fibers establish the connection between the senses and the muscles through the nerve center.
The nervous system of higher animals is also the product of the upward development of the simple nervous system of lower animals.
As far as is known, coelenterates have begun to differentiate nerve cells, which are connected to each other in a network and distributed in various parts of the body, called the scattered nervous system. When any part of its body is stimulated, the whole body can cause a reaction, called generalized reflex. As we all know, coelenterates such as jellyfish have evolved to be able to move freely, and being able to move freely makes coelenterates actively swim to places where food is abundant, so as to obtain more energy, which is more energy to promote the differentiation of nerve cells. The evolution of later life also illustrates this.
Since then, the nervous system has undergone a slow evolution for a long period of time, gradually appearing ganglia and complex sensory organs such as eyes, antennae, etc. To the simplest vertebrates such as round-mouthed fish, fish and amphibians have emerged brains that develop from head ganglia, which, although simple in structure, have differentiated into ten pairs of cranial nerves. The appearance of the brain is still more effective energy-promoting. As mentioned earlier, the evolution from the soft body to the spine is a milestone in the evolutionary history of life, and with a mouth that can be opened and closed freely, the ability of life to absorb energy has been greatly improved. To reptiles, due to the appearance of the lungs, metabolism was able to take place in a completely free air, the ability of life to obtain energy was further improved, the nervous system has evolved twelve pairs of cranial nerves, and the cerebral cortex has emerged. The cerebral cortex is the site of analysis and synthesis of higher animals after receiving various stimuli, and is the headquarters of higher neural activity, directly or indirectly controlling the physiological functions of various organs of higher animals. But the brains of reptiles are still not large, and the brains of dinosaurs weighing dozens of tons weigh less than half a kilogram. In mammals, the evolution of the nervous system was a big step forward than that of reptiles. Not only is the brain volume increased, but the sulcus on the cerebral cortex is more complex, so the sense and reflection are more sensitive. Its evolution is not isolated, but with other systems of the body interconnected, mutually reinforcing, as mentioned above, to mammals, the digestive system has been fundamentally reformed, their teeth differentiated into incisors, canine teeth, premolars and molars, each with different functions, can make food in the mouth first preliminary processing, easy for gastrointestinal digestion and absorption. The gastrointestinal tract of mammals has also evolved. Become more advanced and complex. The circulatory system has also undergone a fundamental change, the real double circulation, the heart is divided into two atriums and two ventricles, oxygenated blood and hypoxic blood are no longer mixed. The complete double circulation makes the mammalian vertebrate body structure and function more perfect. The systemic circulation is responsible for transporting oxygen, nutrients and metabolic waste, and the pulmonary circulation is responsible for gas exchange, so that the blood supply oxygen is sufficient, creating conditions for maintaining a constant temperature and a strong metabolism. All of these revolutionary evolutions, along with other beneficial evolutions, contributed to the evolution of the mammalian nervous system.
The human brain is the most outstanding product of biological evolution, and its weight is not too large, the average is one. Four kilograms, but the cerebral sulcus is thick and deep, very complex, and is the birthplace of human consciousness and intelligence. Consciousness and intelligence are fundamental characteristics that distinguish humans from other animals. This evolution of the brain is also due to the increased ability of humans to obtain energy, but compared to humans and other mammals, we can see that our teeth and nails are almost useless. Our senses also have nothing to boast about. Our eyesight is inferior to that of most birds, and our hearing is inferior to that of bats; as for our sense of smell, a dog with a no-nose can also make us bow to the wind. So what is the reason for the improvement of the ability of one of the apes to obtain energy and thus generate minds and evolve into humans?