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.
You will find more topics on industrial melanism and natural selection on our website, which will help you to have a better understanding of evolutionary mechanisms. Additionally, you can download these study guides in PDF format to go through them at your convenience. You can also download our Vedantu app for convenient access to interactive online sessions for better clarity.
FAQs on Industrial Melanism
1. What is industrial melanism, and what is its most famous example?
Industrial melanism is an evolutionary process where a species' population in a polluted area becomes darker over time. This happens because the darker colouring provides better camouflage against soot-covered surfaces, helping the organism hide from predators. The most famous example is the peppered moth (Biston betularia) in England during the Industrial Revolution.
2. How did pollution in England affect the peppered moth population?
Before the Industrial Revolution, light-coloured moths blended in with lichen-covered trees. After industrial pollution covered trees with black soot, the dark-coloured (melanic) moths became better camouflaged, while the light ones were easily spotted by birds. As a result, the dark moths survived and reproduced more, causing their population to increase dramatically.
3. What is the scientific name of the moth famous for showing industrial melanism?
The scientific name of the peppered moth, which is a key example of industrial melanism, is Biston betularia. There are two main forms: the light-coloured (typica) and the dark-coloured (carbonaria).
4. What type of natural selection does industrial melanism represent?
Industrial melanism is a classic example of directional selection. This is a type of natural selection where an extreme phenotype (in this case, the dark colour) is favoured over other phenotypes, causing the population's genetic variance to shift over time in that new, favoured direction.
5. Did individual moths actually change their colour to adapt to the polluted trees?
No, this is a common misunderstanding. Individual moths did not change their colour during their lifetime. The change occurred at the population level through natural selection. The gene for dark colour already existed in the population at a low frequency. Pollution simply created an environment where moths with this gene had a higher survival rate.
6. Who first conducted the key experiments to prove industrial melanism?
The most famous experiments demonstrating industrial melanism in peppered moths were conducted by biologist Bernard Kettlewell in the 1950s. He performed mark-recapture experiments in both polluted and clean forests, showing that bird predation was the selective pressure driving the change in moth colour frequency.
7. What happens to the moth population if pollution is controlled and trees become clean again?
When pollution is reduced and the air becomes cleaner, lichens grow back on trees, making the bark lighter. This reverses the environmental pressure. The light-coloured moths are once again better camouflaged, so they survive and reproduce more successfully. This leads to an increase in the light-coloured moth population, a phenomenon known as reverse evolution.
