Darwin, in his book ‘On the Origin of Species’ proposed that evolution occurs through a natural selection process. In this process, modification and variations in characteristic traits enable some organisms to adapt to changing environments quickly. Then they produce offspring and pass on the favourable characteristics to their next generation. Those organisms that fail to adjust to environmental changes get eliminated.
This process is also known as the survival of the fittest since organisms which are fitter and better adapted to an environment can survive and reproduce with success.
Components of Natural Selection Process
There are three crucial components to this process – heritability, reproduction and variation. Let us see what these terms mean.
Variation – Each individual within a population shows variation in characteristics or traits. This component is crucial for natural selection to work as without any differences in features; nature cannot select the better ones.
Reproduction – Individuals with more favourable traits reproduce more organisms than is required. In that way, offspring which have more advantageous characteristics are able to survive so the attributes can be passed through generations.
Additionally, in a population, if the rate of reproduction is high, it will lead to increased competition for resources where only the organisms with desirable traits can survive.
Heritability – During reproduction, children inherit beneficial traits from their parents which enable them to survive and reproduce. Thus, the favourable characteristics are passed on and soon become a common trait in these species.
Even though Darwin was not able to provide explanations on how variations were inherited, subsequent studies on genetics have explained that organisms inherit traits from their parents through replication of DNA sequence.
We also know that new variations in species are created through random mutations and recombination.
Natural selection is influenced by the external environment as organisms develop variable traits to survive in different situations. For instance, industrial melanism is an example of natural selection.
What Is Industrial Melanism?
It can be defined as a phenomenon where arthropods evolved melanism to adapt to high levels of pollution such as soot deposit and sulphur dioxide gas in industrial regions. The dark pigmentation in such organisms allows them to blend with the surroundings better.
Industrial melanism was first observed in the U.K around the time of the industrial revolution. Before the industrial revolution, the peppered moth species which were pale grey were more commonly seen. It enabled them to escape from their natural predators like birds by blending in with their surroundings. In contrast, dark coloured or melanic moths were rare.
However, during the revolution, soot from coal-run industries led to air pollution and darkened the surrounding areas. Consequently, these pale coloured moths were hunted more by their predators as they were unable to disguise themselves by blending against a dark background. It led to a decrease in their population, mainly in the industrial areas.
At the same time, the presence of soot content in the air led to an increase in the population of melanic or dark coloured moth species as they could easily camouflage themselves with the darker background. Thus, the population of melanic moths increased in the industrial areas as they quickly adapted to the changing environment.
Hence, industrial melanism is an example of directional selection where because of environmental changes, a single phenotype is preferred. It causes the allele frequency to move in a particular direction continuously.
However, it was also noted that in areas where the pollution levels were low, the pale grey species did not undergo any changes. Moreover, when hundreds of years later a clean air bill was passed in Britain which led to decrease of soot and pollution in the environment and improvement in the quality of air, the pale grey coloured species made a comeback and soon became the predominant species.
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1. What is Industrial Melanism?
Ans. Industrial melanism is a phenomenon seen in industrial areas covered with soot where organisms evolve to become more melanic to camouflage themselves against darker backgrounds. This helps them to escape predators.
2. What is Natural Selection?
Ans. It is an evolutionary process where individuals who are better suited to an environment survive and produce offspring.
3. What are the Three Types of Natural Selection?
Ans. The three types of natural selection are – directional selection, stabilizing selection, and disruptive selection.