Image: from Wikimedia commons
Patrick Greenfield
09/01/2025 in The Guardian Down To Earth Newsletter
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During Britain’s industrial revolution, the peppered moth became one of the most famous examples of rapid evolution. The black and white insect, widespread in the northern hemisphere, largely disappeared from urban areas in England as its habitat became covered with factory soot. In its place, a black form of the moth dominated, blending in with its new surroundings, better able to hide from birds and other predators. As air quality improved in the 20th century, black and white moths experienced a resurgence in urban areas. For scientists, the humble peppered moth is one of thousands of examples of how humanity is impacting the natural world, forcing other species to adapt to our dominance of Earth. At the end of 2024, I asked researchers for modern day examples they had seen in their work. I received dozens of responses. Shrinking mahogany trees, a brittle star almost exclusively found in beer bottles discarded by fisherman and city snails evolving paler shells to counter city heat were among the most striking examples that we documented in an article this week. But there were many more we did not have space to publish. One fascinating example was offered to me by Dr Irina Druzhinina, senior mycologist with Kew’s Royal Botanic Gardens, who pointed out how the construction of Britain’s railway network in the 19th and 20th century turbocharged the spread of Serpula lacrymans, better known as dry rot fungus. It is a homeowner’s nightmare, causing millions of pounds of damage to UK homes every year by breaking down the parts of timber that give wood its strength. Druzhinina told me the fungus was spread around the country by the growth of train travel. “As railways expanded, large quantities of untreated or poorly treated timber were used in construction, including sleepers, bridges, and railway buildings. These materials provided an ideal environment for the fungus to spread and proliferate,” she explained. “The movement of infected wood in sleepers or crates inadvertently helped the fungus spread across regions. It is why we now have concrete sleepers all around even though the wood is better for railways.” Differences between cities and the countryside was also a common theme in responses, including a recent paper on differences in body sizes among African dwarf chameleons. The urban heat effect, meaning that towns and cities are usually significantly warmer than surrounding rural areas, also featured a lot. Dr. Barbara Gravendeel, a botanist with Naturalis Biodiversity Center in the Netherlands, pointed to the example of dandelions that grow faster and flower earlier in urban areas. “We collected seeds from common dandelion (Taraxacum officinale) individuals along an urban–rural gradient in Amsterdam to study how these plants evolve in response to urban heat. Urban dandelions grow faster at elevated temperatures and require shorter cold periods to induce flowering, as compared to dandelions from rural populations,” she said. Creeping woodsorrel, another common plant in the northern hemisphere, has redder leaves in urban areas to combat heat stress while keeping greener leaves in cooler rural habitat, Japanese researchers found in 2023. Many researchers said there are are likely thousands more examples around the world waiting to be discovered. If you would like to get involved in finding them, citizen science apps like iNaturalist are a great way to help researchers spot differences across large areas. Happy searching. Read more on biodiversity: |
The Peppered moth: a seasoned survivor
Illustrated by: Sabine Deviche
Blending In
You walk over the tan-colored sand of the empty desert. You are mid-stride through a set when a rattlesnake appears out of the sand in front of you, rattling its tail. Luckily it had warned you of its presence. This snake matched its environment almost perfectly, making it very hard to see.

Imagine if that same snake were moved to a green leafy rainforest. The colors that helped the snake blend into the desert will make it stand out against the green environment. It will no longer be camouflaged.
This just goes to show you that camouflage doesn’t work everywhere. What helps you hide in one place might make you stand out in others. So what happens when an animal’s environment changes? Let’s take a look at one animal species that is famous for changing over time to stay camouflaged: the peppered moth.
A Pick of Pepper

It could adapt to these changes in a number of ways. The individuals could move (to try to find trees that match its color). Or the species could have altered behavior, or even change over time to adapt to the new surroundings.
This species has two different adult forms. One form of the species, typica, is a pale lighter color that is peppered with black speckles. The other form, carbonaria, is a much darker color that is peppered with light speckles.
From Light to Dark Moths
Moth collectors in England noted that most peppered moths collected in the early 1800’s were light gray peppered with bits of black. Many years later most of the moths collected were almost completely black.

Scientists bred the moths and figured out that the light-colored form of the peppered moth has different genes from the dark form. The black color of the dark form was due to a mutation in the DNA of the light-colored form.
Once this mutation was present, the dark-colored moths would produce offspring with dark-colored wings. Light colored adults that didn’t have the mutation produced light offspring. But genetics is only part of the story.
A Changing World
During the 1800’s, Europe and America experienced the Industrial Revolution. It was a time of change in manufacturing processes that led to the building of factories.This enabled humans to make many more things much faster.
Coal burning released large amounts of smoke and smog into the surrounding environment.This left a layer of black soot on the once lighter-colored trees. The pollution also killed the light speckled colored lichens that grew on the tree trunks. The tree bark was now exposed and dark without the lichens. How did this affect the peppered moth?
The Pepper in Peppered Moth
Like many moths in forests, the peppered moth tends to rest (or “perch”) on tree trunks during the day. They do most of their flying at night. So it would probably be a good thing if the moths look similar to the trees that they perch on, right? Then they can be camouflaged from birds that want to eat them.
Before the Industrial Revolution, the light peppered moth was common, while the dark form was very rare. The light moths blended in with the light-colored trees. However, the Industrial Revolution changed the tree colors.

Natural Selection in Action
Over time, the dark colored moths became the more common of the two color forms. Natural selection favored the dark individuals, so they were more successful after the trees changed.
Sound a little hard to believe? Well, more observations have come about since these conditions started to reverse, starting in the 1950s. Then, a Clean Air Act was introduced. Since that time, technology and cleaner burning fuels have started to decrease pollution in the areas where the peppered moth lives. The lichen has started to grow again and the black soot no longer settles on the barks of the trees. As expected, the light peppered moth population has recently been more common in the population. This is because it is better camouflaged.
Changing Colors

Scientists like Dr. Henry Bernard Davis Kettlewell used the Scientific Method to test how and why peppered moth coloration changed.
Big cities, big bodies: urbanisation correlates with large body sizes and enhanced body condition in African dwarf chameleons (Genus: Bradypodion)
Abstract
Urbanisation is a major driver of habitat transformation that alters the environmental conditions and selective regimes of the habitats where it occurs. For species inhabiting urban habitats, such alterations can facilitate adaptive responses in their phenotypes, including their morphology. Quantifying potential responses could provide important information for assessing adaptation to urbanisation and may also be relevant to their conservation. Previous studies on African dwarf chameleons (Bradypodion) have shown these lizards to have remarkable adaptive capacity in response to different habitats (e.g. closed canopy habitats vs. open canopy habitats). Several of these species exploit urban habitats, but the extent to which populations are adapting to urban environments has only recently started to receive attention. In this study, we quantify differences in body size and body condition between urban and natural populations of five species of dwarf chameleons. For most comparisons, either females, males or both sexes from urban populations were longer, heavier and/or had better body condition than those from natural populations. In the remaining cases, there were no differences in these traits between populations. Our findings conform with the emerging paradigm that urbanisation positively correlates with enhanced lizard body sizes and condition, although the reasons for this may be complex. Nevertheless, our data provide an avenue for future research into investigating the potential factors (e.g. food supply, predation risk, etc.) that facilitate the trends we observed.
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