What kind of book is the theory of evolution and what does it say?

Darwin's theory of evolution consists mainly of four sub-theories:

First, the general theory of evolution: species are changeable, existing species are changed from other species, and one species can become a new species. This has long been confirmed by observations and experiments in biogeography, comparative anatomy, comparative embryology, paleontology and molecular biology, and we can now even directly observe the emergence of new species in the laboratory and in the field.

So, this is a scientific fact that is as reliable as "the earth is round" and "matter is made up of atoms". Today, with the exception of a very small number of people who ignore the facts because of religious prejudices, there are practically no biologists who deny the fact of biological evolution.

Second, the doctrine of common ancestor: all living things come from a common ancestor. Molecular biology discovered that all living things use the same set of genetic code, and biochemistry revealed a high degree of consistency at the molecular level, which ultimately confirmed Darwin's vision.

So, this is also a generally accepted scientific fact.

Third, the doctrine of self-selection: natural selection is the main mechanism of evolution. The existence of natural selection has been confirmed by countless observations and experiments, so this is also a scientific fact.

However, it is now generally accepted in the academic community that the use of natural selection is not as widespread as Darwin assumed. Natural selection is the mechanism of adaptive evolution (i.e., the adaptation of organisms to their environment), and for non-adaptive evolution, there are other mechanisms such as genetic drift. That is, all evolutionary phenomena cannot be explained by natural selection.

Considering that adaptive evolution is the core phenomenon of biological evolution, it is also valid to say that natural selection is the main mechanism of evolution.

Fourth, the gradual change theory: the pace of biological evolution is gradual, a gradual improvement process that accumulates small dominant variations under the action of natural selection, rather than a leap. This is one of the more controversial parts of Darwin's theory of evolution.

During Darwin's lifetime and for a long time after his death, most biologists, especially paleontologists, believed that biological evolution was capable of leaps, that new forms and organs were the result of large leaps, rather than small variations that accumulated slowly and gradually by natural selection. Some paleontologists, including Huxley, hold this view because of their emphasis on the discontinuity of fossil organisms. For some time after the birth of genetics, early geneticists also generally accepted the theory of transition because of their emphasis on the discontinuity of inherited traits.

In the 40s of the 20th century, the doctrine of "modern synthesis" successfully combined the doctrine of genetics and natural selection, and the theory of gradual change gradually prevailed. But near.

In the past two or three decades, the research of paleontology and evolutionary developmental biology has shown that the process of biological evolution is likely to exist in both gradual and leap patterns, and the theory of leap is on the rise again. However, the evolutionary transitions, except in some very special cases (such as the emergence of new species through the hybridization of plants), do not refer to the evolution that occurs between generations or generations, but may have taken thousands, tens of thousands, or even millions of years, but are very brief in terms of geological time.

The theory of evolution is a set of theories used to explain the variation of organisms from generation to generation, also known as the theory of evolution. It refers to the doctrine of the gradual evolution of living things from low to high, from simple to complex. Includes:

Early Species Theory.

Darwin's theory: "natural selection, survival of the fittest", there is a struggle for survival between organisms, the adaptors survive, and the unfit are eliminated, this is natural selection. It is through heredity, mutation, and natural selection that living things evolve and develop from low to high, from simple to complex, and from few to many.

Modern Integrative Evolution.

A man and a woman having a baby together is an example of evolution.