When did humans evolve?

Chapter 3 - The evolution of the brain of living beings

"Life is precious, and love is more valuable. If it is for freedom, both can be thrown away." Believe this sentence Everyone is familiar with it. For a literary person, this is beautiful. But to a scientist, this is nonsense. Nothing is more valuable than life, and life is a miracle you cannot imagine.

I once wrote this in my poem "The Frog in the Cave":

To live - that is unimaginable even with all my wisdom

To die is Some wisdom cannot bloom despite all its efforts

I live

I smile

The definition of life in contemporary science is this:

Life generally refers to a type of phenomenon composed of one or more cells composed of organic matter and water, which has stable material and energy metabolism (can stably obtain material and energy from the outside world and discharge waste and excess heat generated in the body to the outside world) A semi-open material system that can respond to stimuli and reproduce itself (reproduce).

Life individuals usually experience birth, growth and death. Life populations evolve through natural selection through the replacement of individuals from generation to generation to adapt to the environment. Viruses will show signs of life when they have a host to live on; but they will not show signs of life when there is no host to live on. Therefore, viruses are a wonderful creature between life and inanimate substances.

Now let’s take you to understand the development of life and the emergence of consciousness.

I have been thinking about brain problems since I was very young. Why should I sleep when I can wake up in the morning? Why do roosters crow? Are chickens conscious? To understand these, the first thing to explore is the brain.

The evolution of the brain of living organisms

Whether it is for animals or humans, the evolution of the brain is the fundamental manifestation of survival ability. Therefore, the most important thing about human evolution is the evolution of the brain. Not hands, not legs. But the evolution of hands and legs will inevitably promote the evolution of the brain.

Observing the current living world, it is not difficult for us to draw the following conclusions:

1. The living beings with larger relative brain capacity are smarter.

It’s very simple, from plants, bugs, mice, chickens and ducks, cats and dogs, tigers and leopards, elephants, whales, and finally humans. You will find that the consciousness ability of living entities is gradually improved. You may ask again, why are elephants and whales dumber than humans, but their brain capacity is much larger than humans?

The answer is: First of all, this is a general principle, not absolute.

Second, we are talking about relative brain capacity. It is calculated by comparing brain volume with body volume.

2. From a classification point of view, there are five kingdom systems: prokaryotes, protists, fungi, plants, and animals.

The animal kingdom has more complex brain activity and better evolution. The animal kingdom can be divided into two categories: invertebrates and chordates. The subphylum Vertebrates includes Cylostomata, Fish, Birds, Reptiles, Amphibians, and Mammalia. The brains of mammals are stronger than others.

Next let’s talk about the evolution of the brain.

As for the origin of life on earth, I agree more with Miller’s experiment. Miller believed that life originated in water. So regarding the evolution of the brain, we also need to start from the ocean or lake.

First of all, the original brain was just a group of cells in marine organisms that could conduct electric current.

After a long period of development and evolution, this type of tube that can conduct current developed into a prototype brain.

The real brain did not appear at this time. After a long period of evolution and development, the real brain finally appeared. He appears on a fish or other aquatic life form.

This is the prototype of the human brain. This is also the beginning of great development of the brain. From this, the brain evolved and entered the era of high speed in the ocean. The cell structure also changes drastically at this time, and nerve branches form. Many independent sheaths form around the nerve.

Vicissitudes of life, changes in terrain, and changes in the environment eventually forced some aquatic life forms to come to land as a last resort. Crawling, standing, the brain evolved into the land high-speed era. Dinosaurs also slowly formed at this time.

Dinosaurs also had such brains.

In order to adapt to environmental changes and survive, after a longer period of time, mammals were born. Their brains are further developed and can better adapt to the environment.

The most perfect brain is the brain of an animal called a human. That's our own brain. It has a cortex, criss-crossed with ravines, and neurons connected to each other, forming a complex system.

At this point, the evolution of the brain has not stopped. Because life continues, life is still developing. The environment is still changing, so our brains are still evolving. The picture comes from the video "Brain Evolution" of Discovery.

To summarize here, the evolution of the brain of living organisms is definitely a long process. The asymmetric development and evolution of cells under the influence of the symmetry breaking mechanism is the prerequisite for us to develop a developed brain.

The modern view is that the evolutionary process of life on earth is as follows: evolving from the most primitive cell-less structure to prokaryotes with cellular structures, from prokaryotes to eukaryotic single-cell organisms, and then Developing in different directions, the kingdoms of fungi, plants and animals emerged.

The plant kingdom evolved from algae to gymnosperms to ferns, gymnosperms, and finally angiosperms.

The animal kingdom evolved from primitive flagellates to multicellular animals, from primitive multicellular animals to chordates, and then evolved into higher chordates, vertebrates. Fish among vertebrates evolved into amphibians and then reptiles, from which mammals and birds evolved. One branch of mammals further developed into higher intelligent creatures, apes. This is the rudiment of man.

As for the way of evolution, it is generally believed that there are two types: gradual and explosive.

Gradual formation, that is, one species gradually evolves into another or multiple new species; the other is explosive formation, such as polyploidy, which is the most common form of sexually reproducing animals. occurs rarely in plants, but is quite common in plant evolution.

About half of the plant species in the world are polyploid due to sudden changes in chromosome number. The formation of species (macroevolution) often manifests as an explosive evolutionary process (such as the Cambrian explosion), whereby old types and groups are replaced by new types and groups that develop rapidly.

Through fierce struggle for survival, the creatures in nature survive, and those who are not adapted are eliminated. This is natural selection. Progressive evolution is a basic concept in Darwin's theory of evolution. Darwin believed that in the struggle for survival, the gradual accumulation of adaptive variations will develop into significant variations, leading to the formation of new species. Because "natural selection can only act by accumulating slight, successive, beneficial variations, it cannot produce huge or sudden changes; it can only act by short, slow steps."

Modern evolution theory adheres to Darwin’s idea of ??gradualism and the creative role of natural selection, emphasizing that evolution is a long-term genetic change in a population, and believes that it is through mutation (gene mutation and chromosomal aberration) or genetic recombination and selection. Due to factors such as drift, migration, and isolation, the genetic composition of the entire population will change, causing reproductive isolation and evolving into different species.

Explosive evolution is the discovery of fossils. In the history of evolution, there has been a relatively quiet period of evolution for a long time, and there are very few fossils of new species; sometimes a large number of species fossils appear in a relatively short geological time, such as the Cambrian explosion.

The Cambrian Period is the first period of the Paleozoic Era. Research evidence shows that the Cambrian period lasted from about 544 million years ago to 505 million years ago. The earliest life on earth appeared about 3.8 billion years ago. During the 3.2 billion years from 3.8 billion years ago to 600 million years ago, the rate of biological evolution was very slow.

The earliest prokaryotes may have appeared 3.5 billion years ago. The earliest eukaryotes may have appeared 2 billion years ago. From then until 600 million years ago, almost all living things on earth were single-celled organisms. Starting from the Cambrian period, a wide variety of multicellular animals suddenly appeared on the earth. People call this phenomenon the "Cambrian explosion", also called the "Cambrian explosion".

This theory believes that the discontinuity of fossils is a true reflection of history, which shows that the evolution of organisms is discontinuous. New species appear rapidly in a short period of time, followed by a long period of evolutionary stagnation. Until another burst of rapid speciation occurs.

The evolution of living things includes both slow gradual progress and sharp leaps; it is both continuous and discontinuous. The entire evolutionary process is characterized by the dialectical unity of gradualness and leap forward, continuity and discontinuity.

We can only trace the remnants of the past to infer the evolution of life and the evolution of the brain. Think about how boring and long this process is, and then touch yourself, you should be sincerely proud, because you are the most successful life on this earth!

Excerpted from the popular science work "Exploring Life" by Ling Dunzhe, an independent scholar, poet, writer, and famous Chinese studies teacher.