Normally, farther, and in general just able

Normally, adaptations occur over thousands or millions of years. However, drastic changes in the environment can shorten the time period in which a change comes about. In such cases, we can learn a lot about the evolutionary process and how natural selection drives it forward.

Designed to Blend In

Wouldn’t it be great to be a chameleon? You could just blend in with whatever was around you. No need to run from a hungry predator – you just disappear from sight! Unfortunately, other animals don’t have this ability, so they have other ways of camouflaging themselves to blend in with their surroundings. Usually this works pretty well, because if you don’t blend in, you get eaten!But imagine that all of a sudden, the environment around you is drastically altered. Your camouflage is no longer beneficial if it doesn’t help you hide. Worse yet, it may even make you stand out like a sore thumb, advertising your whereabouts like a big neon sign.

The Peppered Moths

This is exactly what happened to the peppered moths in England during the Industrial Revolution. Peppered moths got their name because they are a light gray color and look like they have been sprinkled with pepper. This coloration pattern helped the moths blend in with light-colored trees and lichen, protecting them from predators. This was a very good camouflage because the moths looked very much like the trees and lichen they rested on, sort of like a permanent chameleon color.This all changed with the Industrial Revolution in England, which began in the late 1700s and ended about 80 years later. The Industrial Revolution was a time of great change. Machines replaced much of the work that was done by manual labor.

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Chemical manufacturing was increased, and biofuels, such as wood, were traded in for new fuels, like coal. Life was greatly improved for many people as power became more efficient and affordable. People were earning more money, traveling farther, and in general just able to get more done.However, the pollution created by the Industrial Revolution had serious consequences both for humans and the environment.

Remember the peppered moth? Well, the lichens they rested on began dying, and the trees became covered with soot. The soot turned the trees black, making the light-colored moths stand out in stark contrast. This made them easy targets for predators, and their numbers began to dwindle.At the same time, though, the peppered moth was also thriving. How is this possible? Well, just like with any species, there are variations among individuals.

Among the peppered moths, there were individuals that were much darker than the normal light color with black spots. These darker individuals would have stood out against the light-colored lichen and trees, but once the trees became darker in color, the darker moths suddenly became the ones blending in. This means they were less likely to be eaten by predators, which inevitably means they lived longer and could reproduce more successfully. So, while the light-colored moth was disappearing, the dark-colored moth was thriving.

Natural Selection in Action

Natural selection is a process in which organisms best suited to their environment are more likely to survive and reproduce.

Natural selection is the mechanism for evolution, because over long periods of time, populations become better-adapted to their surrounding environment. Keep in mind, evolution does not select for the ‘best’ organisms – neither the light or dark moth was a better moth – they were just different variations within a species. Instead, it’s the demands of the environment that either support or work against specific traits in a population, and rarely do those changes happen as quickly as they did with the peppered moths. Normally, evolution of a species occurs over thousands, if not millions, of years. But sometimes, circumstances can be so extreme that changes come about much sooner, as they did during the Industrial Revolution.Because the population of peppered moths shifted from one extreme variation to the other (from the very light color to the very dark color), we call this directional selection.

Instead of a blended version of the coloration, or an increase in the dark variation without a decrease in the light variation, the selection was for the moths on the other end of the color ‘spectrum’ within that population. The darker trees provided more camouflage, so the adaptation was ‘directed’ toward the darker moths that blended in better.Since the Industrial Revolution, many environmental regulations have been put into place that reduced pollution from factories and other sources. This has given the light-colored moth a chance for a much-needed comeback, and today, they are common once again.

Lesson Summary

We have learned a lot about natural selection and evolution from studying the peppered moths in England. During the Industrial Revolution, the once-common light-colored moth became the minority in the population. Originally, individuals with this color variation thrived because they blended in with their surroundings very well. But once pollution became rampant, the trees became black with soot, and the light-colored moths stood out like a sore thumb.At the same time that predation became more common for the light-colored moths, the dark-colored peppered moths were thriving. Instead of being the ones that stood out on the trees, they now blended into their surroundings and were better able to survive.

Learning Outcomes

Once you’ve finished with this lesson, you will have the ability to:

  • Define natural selection and directional selection
  • Summarize how the Industrial Revolution impacted the peppered moths in England
  • Explain what this impact to the peppered moths teaches us about evolution
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