Question

Select the examples related to natural selection from those given below.

1. Pinna reduced in man
2. Industrial melanism
3. Drug resistance in bacteria
4. Snakes without limbs
5. Sickle cell anemia and malaria

• A. 1 and 5 only
• B. 2, 3 and 4
• C. 2, 3 and 5
• D. 5 and 3 only

Answer 1

The correct option is C 2, 3 and 5

The term natural selection was coined by Darwin to describe the process by which nature selects those individuals with favourable variations (characters suitable for the environment), survive and reproduce at a higher rate. Common examples of the natural selection are as follows:

• Industrial melanism (melanization in peppered moth): It is used to describe the evolutionary process of how natural selection favoured dark-winged moths. Prior to industrialisation, there were more light-winged moths. During the post industrialisation period, the tree trunk became dark due to industrial smoke and soots. White winged moths are easily detectable and did not survive due to predators whereas dark winged moths survived because they were less seen by predators against a dark background.
• Drug resistance in bacteria: The drugs which destroyed bacteria in the beginning become inefficient in course of time. Due to continuous exposure to the same drug, most of them developed drug resistance, they survived and transmitted these characters to the offspring to produce resistant (tolerant) populations.
• Sickle cell anemia and malaria: Sickle cell anemia is an inherited red blood cell disorder that affects hemoglobin, the protein that carries oxygen through the body. Individuals who are homozygous for sickle cell anemia die at an early stage while in heterozygous condition, the RBC containing abnormal hemoglobin becomes sickle shaped. In fact, when an RBC becomes sickle shaped, it does not allow malarial parasites to survive effectively so that these individuals are able to cope with malaria infection much better than normal people. The process of natural selection thus maintains the abnormal form of hemoglobin along with normal in a region where malaria is common.

Reduced pinna in man and absence of limbs in snakes supports the theory of inheritance of acquired characters. This theory was put forward by Lamarck.

• Snakes lost their limbs because limbs are of no use in crawling and burrowing animals instead it produces a hindrance for their normal life. So, these became gradually reduced and finally disappeared.
• Pinna are reduced in man but are well developed in dogs and elephants because these animals use their pinna to collect sound waves from the surroundings more than that of humans.