The evolution of animals, what are the animals that have evolved

It's true that species evolve, but what are the reasons for evolution? Why do species mutate? Why do species evolve from simple to complex, from low to high?

Before Darwin, there were evolutionists who tried to answer this question, but their answers were either factual or far-fetched. Darwin summed up and discarded the theories of his predecessors, and paid attention to absorbing nourishment from the academic ideas of other disciplines, and after years of hard exploration and intense thinking, he put forward the theory of natural selection to explain the fact of biological evolution. The theory of natural selection mainly includes the following three harmonious and unified contents:

1) The theory of the struggle for survival. The contradiction between excess reproduction and limited living conditions is one of the external reasons for the elimination of species on Earth.

2) The theory of hereditary variation. Although the mechanism of variation is not clear, the fact that variation is widespread is undeniable, and Darwin used it to explain the intrinsic reasons for the evolution of species.

3) The theory of survival of the fittest. The conditions of existence are always changing, and if the variation of the species is adapted to the changing environment, then it will develop victoriously in the struggle for survival; If the species is not adapted to the conditions in which it is alive at that time, then it tends to decay or perish.

In this way, Darwin gave us a general picture of the mechanism of biological evolution based on the facts and contradictions of nature itself, and various key questions were more reasonable and supported by facts in his case. How do new species emerge? Because the old species mutate.

Why are so many species extinct? Because they can't withstand the pressure of the struggle for survival. Why is the relationship between living organisms and the environment so harmonious?

Because some of the countless variations fit the choice of the environment. As to why the lower types of organisms are everywhere, Darwin wrote: "It is not difficult to understand, because natural selection, i.e., the survival of the fittest, does not necessarily involve progressive development—natural selection makes use only of those variations that benefit organisms in complex life relations." ”

Evolutionary theory: Usually refers to the theory of evolution in the biological world, also known as "evolutionary theory", formerly known as "natural evolution theory". The term evolution was first coined by the French naturalist Lamarck (1744-1829); The book "On the Origin of Species" by the British naturalist Charles Darwin laid the scientific foundation for the theory of evolution.

Darwin believed that the dominant force in biological evolution was natural selection. The development of modern biological science has further developed the theoretical research on the evolution of the origin of life, species differentiation and formation, and it is believed that organisms originally evolved from non-living things, and that all kinds of organisms living in modern times have a common ancestor, and in the process of evolution, through variation, heredity and natural selection, organisms have changed from low to high, from simple to complex, and from few to many species. Engels spoke highly of Darwin's theory of evolution and regarded it as one of the three major developments in natural science in the 19th century.

Ever since there was an animal (creature), evolution has begun!

Evolved animals are bed bugs, Kodiak brown bears, dogs, lizards.

1. Bed bugs: evolved to resist pesticides

A study by the University of Massachusetts in the United States found that the number of bed bugs in New York has increased 250 times, and it is more resistant to pesticides than bed bugs in Florida. This is because they have changes in the genes that control the elasticity of nerve cells, which means they produce higher levels of enzymes that remove toxins.

2. Kodiak Brown Bears: Getting smaller and smaller

The Kodiak brown bear, sometimes called the Alaskan brown bear, is one of the largest species of bears in existence today, with the largest known Kodiak brown bear on Earth weighing more than 680 kilograms, in fact, it is much smaller today than it used to be. In 1990, the National Geographic magazine in the United States wrote an article by Douglas Chadwick that the average size of the Kodiak brown bear was shrinking year by year.

Kodiak brown bears are native to some of Alaska's remote islands, so what is the reason for their smaller size today? In fact, the reason for their evolution is clearly due to humans, especially hunters. Hunters hunted more brown bears and left smaller ones.

The brown bears that are left behind usually have more miniaturized genes. This also leads to the smaller and smaller size of its offspring.

3. Dogs: a large number of artificially bred different species

Dogs are probably the most famous example of direct human intervention, and they are good friends of humans. But there are a large number of dog breeds that have been bred by humans. They used to be wolves that could grow up to meters long and weigh up to 54 kilograms, and over the centuries humans have controlled the elements of their reproduction, breeding many dog breeds that are suitable for different fields.

Over the centuries, a wide variety of dog breeds have been born.

Previously, most bred dog breeds had a specific purpose, and the first VIPs even had strong mouths that could be used to help with hunting; In the 18th century, there were even Dalmatians with super stamina to run with horse-drawn carriages, which was a symbol of wealth; Pit bulls, on the other hand, came into existence to help farmers control their livestock.

With the decline in the dependence on the labor force of dogs, dog breeds began to appear in large numbers for the main purpose of accompanying humans and providing them for entertainment. For example, Chihuahuas and Hiromi appear with their particularly small stature. But such breeding also brings a number of health problems to dogs.

4. Lizards: The legs become longer, and the attachment ability of the feet becomes stronger

Unlike dogs, which take hundreds of years for all animals to evolve slowly, animals like lizards are much more adaptable. They can also reproduce at a very fast rate, and therefore evolve faster, with 100 generations of reproduction in 30 to 40 years.