What is the peppered moth evolution, and why is it so important?

Written by Maxwell Martinson
Published: October 28, 2022
© Marek R. Swadzba/Shutterstock.com
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Let’s say you’re confident in your understanding of the theory of evolution.

Imagine strolling into a Christmas party, only to be greeted by your grandmother who quickly notices the image on your shirt; It’s the classic graphic of five hominids, each one gradually standing more upright than the last.

It starts with a chimp and ends with the form of a human being. You wear this shirt because you think evolution is fascinating— it’s even a key aspect of your worldview.

Your grandmother says, “So, you think we used to be monkeys, huh?” You hesitate to respond, so she goes in for the kill and whispers “why don’t you show me some proof?”

Half-learned data points skirt through your mind, and you’re left scrambling for an answer. She scurries away… victorious.

If you can relate, you’re in the right place. We’ve got a beautiful example of short-term evolution through natural selection. It’s one you might’ve heard about before, but we’re going to take a deep dive.

Let’s look closely at peppered moth evolution, see why it’s so important, and hammer in the key points so you’re ready the next time someone presses you on well-understood and research-backed science.

Peppered Moth Evolution

The Peppered moth has tiny black spots on its wings, hence, the name Peppered Moth.

©Marek R. Swadzba/Shutterstock.com

The key idea is that peppered moths adapted to the Industrial Revolution by rapidly changing colors. That’s the headline that you might remember from your high school science class.

But how does this example tie into evolution, specifically? Further, what are the environmental factors that caused it to occur?

Peppered vs. Black Moths

Up until the early 1800s, peppered moths were predominantly white with black speckles. The black freckles along their wings and back are clearly the reason they were named “peppered moths.”

The peppered pattern blends well with the tree bark and lichen of Britain where these moths live. This camouflage allows them to rest on trees and shrubs with a smaller chance of being eaten by birds.

It was extremely unusual to see an entirely black peppered moth before the mid-1800s. The black mutation was so rare, in fact, that it wasn’t until 1848 that someone first documented a black peppered moth.

If there were any unique black moths flying around, odds are that they would’ve been picked off by birds before they could reproduce. So, the “black” gene lay dormant for countless years, causing unlucky recipients to be plucked and eaten whenever it was expressed.

As a result, almost all peppered moths in Britain were speckled up until the pollution of the Industrial Revolution could take its toll. The Industrial Revolution changed the moths’ environment, and this shifted the ecosystem in such a way that the black gene was rewarded.

Let’s find out how that happened.

The Industrial Revolution & Evolution

A Melanic Peppered Moth sitting on a leaf. Dark colored Peppered Moths increased over time, a result of industrial melanism.
Dark colored Peppered Moths increased over time, a result of industrial melanism.

©Steve McWilliam/Shutterstock.com

The Industrial Revolution was inarguably one of the most significant periods in human history. It occurred from roughly 1760 to 1840, introducing new energy sources, transportation routes, trains, the idea of mass production, and drawing the template for life as it’s lived in modern first-world countries.

The revolution was followed by an industrialization period which still contributes to most of human society’s greatest failures and successes. Namely, it was a brutal time for the lower class and just about anyone who wasn’t in a position of extreme power. As it turns out, it was a tough time for city ecosystems as well.

Ecosystems suffered because early industrialization relied heavily on coal. Monstrous coal smokestacks rolled constant and massive clouds of black dust into the air—eventually coating the buildings, trees, and rocks of surrounding areas.

This was a great thing for the black peppered moths, however.

Trees coated in black soot made it easy for standard peppered moths to be identified by passing birds. Those moths were previously camouflaged, but they had nowhere to hide after soot coated their trees and rocks.

On the other hand, the black peppered moth was suddenly invisible to the birds. As the peppered moths died, black moths reproduced and redistributed the gene pool. The result was an abnormally speedy shift in the appearance of the peppered moth population.

In 1848, black moths were thought to make up roughly 2% of the population. By 1895, fewer than 50 years later, black moths constituted around 95% of the population.

It was also observed that moths in neighboring towns without as much pollution didn’t experience the change. The places where smog had darkened tree bark were the places where moths evolved to be black.

The Basics of Natural Selection

The habitat of the Peppered Moth usually consists of tree bark which makes their camouflage perfect for protection.
Before the Industrial Revolution the speckled peppered moth blended right in with its environment.

©Henrik Larsson/Shutterstock.com

Here’s where you can start taking notes for the next time someone challenges you.

Natural selection is the environmental force that pressures populations to shift and adapt. This leads species to split into countless branches, producing new species and contributing to the rich diversity of life on earth. But how does it work?

Genetic Variance

Start with the fact that every member of a particular species has similar genes to any other individual in that species. Our genetic code dictates most aspects of our lives, particularly when it comes to our physical traits.

Your genes are very similar to the genes of the next stranger you pass on the street. The same is true for any bunny that hops past another bunny. Every human shares about 99.9% of their genetic material with every other human.

Still, each species contains a great deal of genetic variation as well. In fact, no two individuals in any species are exactly the same. Identical twins are the same at birth, but their genes even express distinctly after birth based on environmental factors.

Variation expresses itself through emergent genes that have been dormant, or through genetic mutations that occur spontaneously. Our genes also adjust over our lifetimes through changes in epigenetic markers.

A gene mutation is “an alteration in the sequence of nucleotides in DNA.” When an alteration occurs, the individual gets a different trait. That trait will be more or less successful for the individual’s life depending on their environment.

Environmental Pressure

If the gene helps the individual survive in a specific environment, the environment has selected that gene. The individual with the life-affirming gene survives and reproduces, whereas individuals with disadvantageous genes might not.

This is where the term “survival of the fittest” comes from.

A shift in genetics could also pressure an individual to migrate or behave differently, and that leads the individual and its offspring to deviate. Groups that deviate start to mate and adjust, eventually becoming so distinct from the original gene pool that they form their own species.

This is a simple overview of the fundamentals. It gets much more complicated, but the ideas above are key principles. It seems pretty intuitive, right?

The trouble is that it happens over such a long period of time, so people aren’t able to witness it in most cases. Also, the idea that we evolved from primates, shrews, fish, or bacteria, gets in the way of many beliefs about creation and the origins of life.

As a result, evidence of this process is very important. It’s also very hard to find evidence that occurs in real-time, in front of our eyes.

A Poster Child of Natural Selection

The evolution of the peppered moth has changed the way that people think about natural selection.

©iStock.com/:mkchan14

It wasn’t until November of 1859 that Charles Darwin published On the Origin of Species. The line of evolutionary thinking hadn’t quite been established by the time peppered moths started to change in the face of the Industrial Revolution.

So, there wasn’t an immediate correlation between black peppered moths and evolution by natural selection. Still, people were taking note of the change and it wasn’t long before it would be used as a prime example of selective pressure.

Criticisms of the ideas in On the Origin of Species were widespread. It wasn’t until 1896 that scientists presented these moths as an example of evolution. That was fourteen years after Darwin had passed away.

Still, the example serves as a potent and intuitive portrait of natural selection.

Peppered moths offered one of the clearest and most observable instances of the evolutionary process. Rarely can we see a species change the genetic material of its population over the course of one human lifetime.

The shift in coloring for various species occurred numerous times throughout industrialization. The phenomenon is called “industrial melanism” and also occurs in sea snakes, ladybugs, and more.

Criticisms & Influence

Naturally, there were a lot of alternative theories about why the moth population changed. Some proposed the idea that the metals or contents of the soot altered the way that moth genes expressed themselves.

Others argued that studies like Kettlewell’s experiment, which claimed that the dark coloring of the moth served as an effective evolutionary camouflage, were impossible to replicate. These types of criticisms exist for most examples and studies on evolution. Still, the tide of opinion has shifted in the United States and around the world, inching toward the acceptance of evolution.

A recent study shows that the majority of Americans now accept the theory of evolution, whereas less than half accepted it in 2010. Shifts toward the acceptance of these ideas might be credited to the dispersion of scientific literature as well as the changing rhetoric of dominant political groups and the ideas they support.

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The Featured Image

The Peppered moth has tiny black spots on its wings, hence, the name Peppered Moth.
The Peppered moth has tiny black spots on its wings, hence, the name Peppered Moth.
© Marek R. Swadzba/Shutterstock.com

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About the Author

Hi! I'm Max and I'm a writer from Minneapolis, Minnesota. I've been freelancing for more than five years and love the freedom and variety that this profession offers. Animals are also a big part of my life, and a lot of my time is dedicated to playing with my cat, Herbie.

Thank you for reading! Have some feedback for us? Contact the AZ Animals editorial team.

Sources
  1. University of Michigan, Available here: https://news.umich.edu/study-evolution-now-accepted-by-majority-of-americans/
  2. Tree Hugger, Available here: https://www.treehugger.com/what-is-industrial-melanism-5116116
  3. Thought Co, Available here: https://www.thoughtco.com/gene-mutation-373289
  4. Nature, Available here: https://www.nature.com/articles/hdy201292
  5. ASU, Available here: https://askabiologist.asu.edu/peppered-moths-game/natural-selection.html