Natural Selection

Natural selection is a mechanism of evolution[i]. Organisms that are more adapted to their environment are more likely to survive and pass on the genes that aided their success. This process causes species to change and diverge over time.[ii]The original theory pushed by C. R Darwin (1809-1882)[iii]and A.R Wallace(1823-1913)[iv].(Then )Darwin published his work about evolution, 「On the Origin of Species 」（On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life）（1859）with the theory of natural selection .

Darwin's theories of natural selection mainly include: An excessive natural rate of multiplication, survival struggle (also called survival competition), heredity and variation, and survival of the fittest.

An excessive natural rate of multiplication (Over reproduction):[v]

Darwin found that all kinds of species in the Earth(on earth) generally have strong reproductive capacity.

For example: elephants is one of species which reproduction slowly(whose reproduction is slow, or, which reproduces slowly). if each female elephant gives birth to 6 cubs in its lifetime (30 to 90 years old),  lived to be 100 years and has the able of reproduction, then their offspring can reach 1 900 millions after 750 years.

If each female elephant were to give birth 6… live until the age of 100, and remain capable of reproduction, then their offspring could reach 1 900 millions

Elephants is one of the species which reproduces slowly. If

Therefore，according to theoretical calculations, even animals and plants that do not reproduce quickly will also produce a large number of offspring in a short period of time and occupy the entire earth. But actually, the number of various species on earth can maintain(will remain in a relatively stable equilibrium) a relatively stable state within a period of time. To explain this phenomenon，Darwin began considered about survival struggle.

Survival struggle:

The reproductive capacity of living things is so powerful, but in fact, very few of offspring of each species can survive. What’s the reason for it? Darwin thought that every species must struggle for surviving(survival) because of over reproduction. They struggle with the natural environment, with the same species for foods or spouses, and with other species. Because of struggle, the living things die large numbers, as a result, only a small number of individuals survived. But which kind of individuals could have survived? Darwin explained by heredity and variation.

Heredity and variation[vi]:

Darwin believed that all the species have the property of producing variation. The basic reason of variation is a change in environmental conditions. Among the various variations produced by living things, some can be inherited, and some cannot be inherited. So which kind of variation can inherit? He explained it by the survival of the fittest.

The survival of the fittest:

The “survival of the fittest” is the core of natural selection’s theory.

Darwin thought that in the struggle for survival, individuals with favorable variations are easier to win in the struggle and then survive.Conversely, variations with unfavorable variations are easy to fail and death in the struggle. That said, individuals which can survived are adapted to the environment, which cannot survive are not adapted to the environment, it is the “survival of the fittest”. Darwin called that in the possess of survival struggle, the survival of who can fittest and the elimination of the unfit by the “survival of the fittest”. He thought that the process of natural selection was a long, slow, continuous process. Since the struggle for survival is constant, so is natural selection, by this way , a new species can be lived ,and also because of the diversity of environment, the way of species adapt to environment are variety，so natural selection forms the diversity of biology.

Darwin's theory of natural selection can stand the test of time because it is based on sufficient scientific facts ，it had a profound impact on academia for more than 100 years。

References:

https://www.nhm.ac.uk/discover/what-is-natural-selection.html

http://www.lscollege.ac.in/sites/default/files/e-content/Principal%20of%20Darwin%27s%20Theory.pdf

[i]Evolution, theory in biology postulating that the various types of plants, animals, and other living things on Earth have their origin in other preexisting types and that the distinguishable differences are due to modifications in successive generations. The theory of evolution is one of the fundamental keystones of modern biological theory.

https://www.britannica.com/science/evolution-scientific-theory

[ii]https://www.nhm.ac.uk/discover/what-is-natural-selection.html

[iii]Charles Robert Darwin (12 February 1809 – 19 April 1882) was an English naturalist, geologist and biologist, best known for his contributions to evolutionary biology.

https://en.wikipedia.org/wiki/Charles_Darwin

[iv]Alfred Russel Wallace (8 January 1823 – 7 November 1913) was a British naturalist, explorer, geographer, anthropologist, biologist, and illustrator. He is best known for independently conceiving the theory of evolution through natural selection.

https://en.wikipedia.org/wiki/Alfred_Russel_Wallace

[v]http://www.lscollege.ac.in/sites/default/files/e-content/Principal%20of%20Darwin%27s%20Theory.pdf

[vi]Heredity and variation are two processes involved in the inheritance of characters from parents to the offspring during sexual reproduction. An offspring produced by sexual reproduction does not completely resemble the parents. But a number of characteristics which are unique to a particular species may be observed in the offspring of that particular species.

https://pediaa.com/difference-between-heredity-and-variation/