- Explanation: Industrial Melanism
- Industrial Melanism in Biston betularia (On Land)
- Industrial Melanism in Emydocephalus annulatus (In the sea)
- Quick peek into the history of Industrial Melanism
- How does Industrial Melanism work?
- How is industrial melanism an example of natural selection?
- What actually is melanin? And, what’s the relation of melanin with industries to cause industrial melanism?
- Microevolution occurs due to Industrial Melanism
- Re-adaptation can occur after industrialization is highly reduced
Explanation: Industrial Melanism
Industrial Melanism is an example of natural selection that refers to a phenomenon in which the animals take on a darker coloration of their skin, fur, feathers due to its adaption towards the increasing industrial pollution over several generations.
In simple words, industrial melanism is the evolution of light body-colored ancestral animal species to dark body-colored descendent animal species that live in habitats surrounded by industrial soot and pollution.
It is a type of adaptation in which the animals naturally adapts to its environment and develops dark pigmentation due to the effects caused by industrial pollution.
This type of natural selection occurs because the industrial pollution due to the excessive release of gasses like sulphur dioxide, carbon, and dark soot deposits causes the factors of the environment like trees, soil, etc. to become dark and soot-covered.
And, this causes the light-colored organisms living in those areas to also get dark-colored naturally through adaptations over generations so that it can better camouflage from their predators.
And in theory, the darker members of the species will become more effectively camouflaged from predators in their soot-coated surroundings. This will help the species sustain over a longer period of time and reproduce well.
This phenomenon of industrial melanism has been well-documented and observed in numerous species that hide from predators by blending in with their backgrounds.
Industrial Melanism in Biston betularia (On Land)
The adaptation of Biston betularia is one of the most famous and well-documented examples of Industrial Melanism.
It is an adaptation where the peppered moths Biston betularia living in an industrial area developed melanin pigment to match their body colors to that of the tree trunks.
Before industrialization in the 1850s in England, there were more white-colored moths (Biston betularia) when the white-colored lichens covered the tree trunks.
But after industrialization in the 1920s in England, more dark-winged moths (Biston betularia) were seen when the tree trunks became dark due to industrial smoke and soot.
The industrial smoke and soot have sulphur dioxide gas and dark soot deposits that killed the white-colored lichens leaving the tree-bark barren.
Soon due to excessive pollution, the soot darkened the barren tree-bark and other surfaces of the tree. This caused the trees to get dark-colored over time.
It was explained that when the soot-covered the tree trunks the dark-colored moths escaped the predators by camouflage. While white-colored moths survived better from predators in the pre-industrial period because white-colored liches covered the trees.
Prior to the industrialization, collection records indicated no reference to white-colored moths. But by 1920s i.e after industrialization, the collection records constituted about 98% of dark-colored moths near many industrialized areas.
This example literally shows that the change in morphology could be directly linked to the change in the industry, and so the process of such an adaptation due to the industries is described as industrial melanism.
Industrial melanism is known from over 70 species of moth that Kettlewell found in England and many others from Europe and North America.
Industrial Melanism in Emydocephalus annulatus (In the sea)
An example of industrial melanism is also seen in the polluted water near industries. This is from the finding done in turtle-headed sea snakes (Emydocephalus annulatus).
Recently in 2017, scientists from the University of Sydney in Australia have pointed the turtle-headed sea snake as the first evidence of “industrial melanism” that has ever been encountered in a marine-dwelling animal.
This study was done on turtle-headed sea snakes (Emydocephalus annulatus) by a team of researchers led by Rick Shine in the bays of Noumea in the South Pacific island of New Caledonia for over 13 years.
It is generally seen that the turtle-headed sea snakes (Emydocephalus annulatus) living in non-polluted water have a black-and-white banded skin appearance.
But, the team had come across the same Emydocephalus annulatus specimens living in polluted waters that were completely black.
This black skin color of the sea-snakes in polluted water was a direct result of contaminants in the waters around them and evidence of animals evolving to adapt to their climate.
The researchers found the same to be true for a similar banded sea snake species called Sea Kraits (Laticauda saintgironsi and Laticauda aggregate), which live in more pristine bays in Noumea.
Quick peek into the history of Industrial Melanism
In 1896, J. W. Tutt proposed Tutt’s hypothesis. He suggested that the peppered moths (Biston betularia) were an example of adaptation due to natural selection. Tutt’s hypothesis stated that the dark moth is more visible to predators on unpolluted trees, while the light moth is more visible to predators on bark blackened by industrial pollution.
In 1900, industrial melanism was first noticed by the geneticist William Bateson. He observed that the color morphology in pepper moths was inherited. But, he didn’t suggest any explanation for the polymorphism in pepper moths.
In 1906, the geneticist Leonard Doncaster described the increase in the frequency of the melanic forms of several moth species between 1800 to 1850 in the heavily industrialized north-west region of England.
In 1924, the evolutionary biologist J. B. S. Haldane constructed a mathematical argument showing that the rapid growth in frequency of the dark-colored pepper moths is due to implied selective pressure on the moths for its adaptation to the industrial pollution.
From 1955 onwards, the geneticist Bernard Kettlewell conducted a series of experiments exploring the evolution of melanism in the peppered moth. He used a capture-mark-recapture technique to show that dark-colored forms survived better than light-colored ones.
By 1973, pollution in England had begun to decrease, and so the dark-colored pepper moths had declined in frequency. This provided convincing evidence that its rise and fall had been caused by natural selection in response to the changing pollution of the landscape.
Between 1979 to 1987, several workers have sought information on the natural resting behavior of peppered moths through cage experiments to know whether peppered moths usually spend the day on tree trunks or not.
Between 2000 to 2004, there were also many additional independent field tests on the relative survival of light-colored pepper moths compared to dark-colored pepper moths, all of which produced results that were as stated in Tutt’s hypothesis of 1896.
How does Industrial Melanism work?
Industrial melanism is actually due to the dark coloration of the melanin pigment of various species occurring due to the various external factors that affect the environment of those species.
Melanin is the pigment that gives the external morphology like fur, feather, and skin its specific color. Various species adapt the pigment color from its environmental adaptation just like you can see in the case of pepper moth due to industrial soot.
Industrial melanism is an evolutionary effect prominent in several moths (arthropods), where dark pigmentation (melanism) has evolved in an environment affected by industrial pollution, including sulphur dioxide gas and dark soot deposits.
Actually the sulphur dioxide gas and dark soot cause some kind of chemical mutational changes of the melanin pigments producing genes in the various moths living in the industrialized regions.
Due to such mutations, the dark-color appearance (melanism) occurs generation after generation.
These mutational changes are actually inherited and so these are able to pass from one generation to another till the industrial pollution remains active.
In genetic terms, the gene for dark color, as in most species, is dominant, and so once the pressure of predation was removed, this variant quickly spread.
But it is seen, if the industrial pollution gets reduced, then the dark-colored moths population again gets adapted to white-colored moths population over time generation after generation.
How is industrial melanism an example of natural selection?
Industrial melanism is a very awesome example of Darwin’s Theory of natural selection.
This phenomenon has been held up high by evolutionists as a clear and undeniable proof of Natural Selection with many pieces of evidence right before our eyes.
Natural selection is a gradual process of how the organisms adapt themselves to evolve to better withstand the environment and pass the adapted characters to their offsprings.
In Industrial melanism too it is seen that adaption is truly and evidently happening right before our eyes in industrially active areas where pollution is a lot.
Just take the example of pepper moths (Biston betularia) which shows an increased population of the descendant dark-colored moths that were adapted from the ancestral white-colored moths due to increase in Industrialization.
Before industrialization white-colored moths were in the tree trunks where white lichens were also present and this helped them to camouflage from their predators.
But, after industrialization, black-colored moths were seen in the tree trunks that had become black without any liches and this had also helped them to camouflage from their predators and escape.
In just over 50 years after industrialization, the dark variety went from making up just 2% of the population to making up over 95%. A massive change/adaptation that could not be explained by any theory other than natural selection and industrial melanism.
So, the occurrence of white-colored moths from dark-colored ones is a fine reason how species adapts to its environment generation after generation in order to better survive.
Tutt’s hypothesis states that the dark moth is more visible to predators on unpolluted trees, while the light moth is more visible to predators on tree-bark blackened by industrial pollution.
Thus according to Tutt’s hypothesis, it is seen that the peppered moths (Biston betularia) were an example of adaptation due to natural selection.
This literally shows that industrial melanism is a very fine example of natural selection.
What actually is melanin? And, what’s the relation of melanin with industries to cause industrial melanism?
Melanin is a complex polymer derived from the amino acid tyrosine. Melanin is responsible for determining external body coloration and is present mostly in the skin to varying degrees.
In the majority of the species, the MC1R gene provides instructions for making a protein called the Melanocortin-1 receptor. This receptor plays an important role in normal pigmentation via. melanin.
The Melanocortin-1 receptor is primarily located on the surface of melanocytes, which are specialized cells that produce a pigment called melanin.
The melanin is actually very sensitive to heat, radiation, pollution, various gases, industrial soot, and these causes dark-coloration of the melanin if highly exposed to.
The degree of dark coloration of the melanin pigment i.e melanism varies from species to species.
Thus, the relation of melanin with industries is that industries can cause the release of pollution, various gases like sulphur dioxide, dark soot which makes the sensitive melanin to cause dark-pigmentation leading to dark-coloration of the external body.
The biochemical process of dark-pigmentation of melanin pigment leading to dark-coloration of the external body of an organism is called melanism.
And, industrial melanism is caused due to increasing industrialization thus leading to the increasing industrial pollution. This eventually can lead to the adaptation of descendant dark-colored species over time from the ancestral white-colored species.
For example: Industrial Melanism in Biston betularia, Industrial Melanism in Emydocephalus annulatus, etc.
Microevolution occurs due to Industrial Melanism
The incidence of industrial melanism is a process called micro-evolution, where selection pressures of predation within a species lead to various changes.
Microevolution is just a small evolution like changing a few genes leading to the creation of new alleles within a population.
Microevolution just leads to the change in allele frequencies in a gene pool. And so small variation can be seen during micro-evolution.
In industrial melanism, the change of white-colored moths to dark-colored ones is a type of small microevolution in which the allele frequency in the gene pool of the moth population has changed over time.
With time (maybe after thousands of years from now), when mixed with genetic drift, other mutations, and other possible selection pressures, this process of micro-evolution can lead to speciation (formation of new species) within the peppered moth population.
If you have two separate populations, one living in industry sooty areas and other in green natural areas, with little mixing between the two populations, random fluctuations could well lead to them becoming distinct species, as seen with Darwin’s finches.
Re-adaptation can occur after industrialization is highly reduced
Re-adaptation means to again adapt due to natural selection but in the reverse direction, if industrialization or the pollution from industries is reduced over time in a particular region.
For instance, if the industrial pollution gets reduced, then the dark-colored moths population again gets adapted to the white-colored moths population over time generation after generation.
Strangely enough, now that modern industries are using cleaner technologies, the moth species are now returning back to the typical variety, as the selection pressure from predation has now reversed.
But, because the allele for the white-color is recessive and requires a copy from both parents, it is a slower process than the initial change. This is known as reverse industrial melanism.
And reverse industrial melanism causes re-adaptation. It will be like going back to the previous state as it was long ago after some time in the future.
If the pollution level decreases, then after a century from now (maybe in the 22nd century) we’ll again find the descendent white-colored moths which will be re-adapted from the present-day dark-colored moths.