5 examples of natural selection of evolution on Earth | biology (2023)


Some of the examples of the evolution of natural selection on Earth are as follows:

A. Genetics of adaptation in industrial melanism (Fig. 7.41):

In the early 19th century (1830s) there was not much industrial growth in England (eg Birmingham) and there was mainly a white-winged peppered moth, Bistort betularia, which could hold its own against birds of prey.


During the day it used to rest on a light oak trunk covered with lichens. But with industrial growth in the 1920s, smoke particles released by industrial smokestacks killed lichens and darkened tree trunks.


Thus, the white-winged Biston betularia became more distinct from birds of prey. Then a dominant genetic mutation appeared in some members of the moth population. This genetic mutation resulted in a melanistic dark-winged moth that had a better chance of survival than the gray moth.

The first melanic form of peppered moth was observed in 1845. These dark-colored moths produced, through differential reproduction, a dark-colored melanic species, Biston carbonaria, which made up 99% of the moth population in 1895.

This replacement of light-colored moths by dark-colored melaneic species due to industrial smoke has been termed industrial melanism. Thus, natural selection favored melanian moths to reproduce more successfully by differential breeding for adaptation in industrial areas of England.

This shows that evolutionary change always has a genetic basis and this genetic variation, when favored by natural selection, allows organisms to adapt to a particular environment, increasing their chances of survival.


It was originally written by R.A. Fischer and E. B. Ford Industrial melanism was tested experimentally in the 1950s by a British ecologist, Bernard Kettelwell. He bred an equal number of dark and light moths. He released one set of these moths in the polluted area (Birmingham Woods) and another set in an unpolluted area (in Dorset).

After a few years, he was able to recover 19% of the light moths and 40% of the dark moths from the contaminated area, while he was only able to capture 12.5% ​​of the light moths and 6% of the dark moths from the uncontaminated area. . . This result shows the differential survival patterns of B. betularia in the contaminated and uncontaminated areas.

He concluded:

(i) Sooty areas offer great protection to melanic forms due to the higher frequency of a dominant gene in industrial areas.


(ii) In uncontaminated areas and rural areas where industrialization has not occurred, the abundance of the gene responsible for light-colored moths has a more selective advantage.

(iii) In a mixed population, the best adapted individuals survive and increase in number, but no variant is completely eliminated, e.g. B. Industrial pollution has not completely eliminated the light-colored moth gene.

It was also reported in many other European countries. Industrial melanism has been identified in around 70 species of moths in England and around 100 species in the US. But since 1956, after clean air legislation was passed, coal has been replaced by oil and electricity .

This reduced soot deposits on tree trunks. Consequently, the number of light moths has increased again with the reduction of contamination. This is called reverse evolution.


B.DDT resistant mosquitoes:

Mosquitoes are known to carry diseases such as malaria and elephantiasis caused by Plasmodium and Wuchereria. Previously, the mosquito population had more mosquitoes sensitive to DDT but less resistant to DDT. When DDT was not used, the DDT-resistant mosquitoes remained dominated by the DDT-sensitive mosquitoes.

But when the use of DDT as an insecticide began (introduced in the 1940s), DDT-resistant mosquitoes had a competitive advantage over their counterparts. Its DDT-resistant trait spread to more and more population groups, so that today the mosquito population is dominated by DDT-resistant ones.

It is also an example of direction selection. According to the principle of natural selection, chemical insecticides would only be useful for a limited time.


C. Sickle cell anemia:

(i) Characters:

Sickle cell anemia is characterized by:

(a) About 1-2% of all red blood cells become sickle shaped.


(B)Early rupture of red blood cells leading to severe anemia.

(c) Normal hemoglobin Hb-A is replaced with defective hemoglobin Hb-S in which the β-chain glutamic acid is replaced with the amino acid valine due to a single base substitution in a gene.

(Also2-The transport capacity of Hb-S is lower than that of Hb-A.

e) the death of the person concerned before reaching puberty.

(ii) Cause. The cause is an autosomal recessive genetic mutation in the homozygous state (HbSHalf pensionS). Die Heterocigoto (HbAHalf pensionS) also have some sickle-shaped cells.

People with sickle cell disease are found mainly in areas of tropical Africa where malaria is very common. Sickle cells from the heterozygote have been reported to kill the malaria parasite. Therefore, heterozygotes can resist malaria infection much better than homozygotes for normal hemoglobin.


The loss of deleterious recessive genes through the death of the homozygotes is compensated by the successful reproduction of the heterozygotes. Therefore, natural selection has preserved it along with normal hemoglobin in malaria-affected areas. It is an example of balancing or stabilizing selection.

E. Antimicrobial resistance in microbes

(Figure 7.44). Joshua Lederberg and Esther Lederberg demonstrated the genetic basis of adaptations in bacteria by culturing bacterial cells via their plating experiment.

Lederberg's experiment had the following steps:

1. They inoculated bacteria on an agar plate and obtained a plate with several bacterial colonies. This disk was called the "master disk."


2. They formed several replicas of this master plate. To do this, they used a sterilized velvet disc mounted on a wooden block that was gently pressed onto the original plate. Some of the bacterial cells from each colony adhered to the velvet cloth.

3. By pressing this velvet onto new agar plates, they obtained exact replicas of the original plate. This is because the bacterial cells were transferred from one plate to another through the velvet.

4. They then tried to make copies on agar plates containing penicillin antibiotic. Some colonies were able to grow on the agar plate and were designated as penicillin resistant, while other colonies did not grow on penicillin antibiotic medium and were designated as penicillin sensitive colonies.

There was a prior adaptation in some bacterial cells to grow in a medium containing the antibiotic penicillin. This preadaptation had evolved in certain bacteria through a random genetic mutation rather than in response to penicillin. This manifested itself only when said bacteria were exposed to penicillin. The new environment does not induce mutations; selects only for preadaptive mutations that have occurred before.


Lederberg's plate replication experiment supported neo-Darwinism and demonstrated that adaptation to penicillin resistance in bacterial cells originated from natural selection of pre-existing mutated bacterial forms.


Penicillin-resistant bacterial cells had no advantage growing in an environment without penicillin. But they had a competitive advantage over others on the penicillin-contour agar plates, as they rapidly multiplied and formed colonies on the penicillin-containing medium.

F. Drug resistance in bacteria. L. Cavalli and G.A. Meccacaro (1952) demonstrated that colon bacteria - Escherichia coli - are 250 times more resistant to the antibiotic - chloramphenicol - than normal bacteria. Cross-breeding experiments confirm that resistance in bacteria is acquired by mutation and is inherited according to Mendelian principles.

Excessive use of herbicides, pesticides, antibiotics, etc. has resulted in the selection of resistant cultivars in a shorter period of time. These are examples of evolution through anthropogenic influences and prove that evolution is not a directed process but a stochastic process based on random events in nature and random mutations in organisms.

Related Posts:

  1. Nature and types of natural selection: recognized by Charles Darwin
  2. Notes on the types of natural selection in evolution (with examples)

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