Question

In a forest full of white birch trees lived a large number of mostly white moths with a few gray spots on them (some had more spots the others). The spotted white moths would land on the birch trees and it was hard to see them because they blended in so well. It made it difficult for the birds (who wanted to eat them) to find them. When the industrial revolution came, the nearby factories gave off lots of smoke and over time the white birch trees became more and more covered with the soot from the smoke. They trees began to look more and more gray. Over this time, it was noticed that the white moths with gray spots, became more and more gray looking in response to this change in their environment. Give a detailed description of how and why the moths turned more and more gray over time. You may want to use terms such as adaptation, survival of the fittest and others from this unit and other questions on this test.(5 points)

Answer 1

The transformation of the primarily white moths with gray spots into more predominantly gray moths serves as a classic example of natural selection and adaptation in response to environmental changes.

### Environmental Change
As the Industrial Revolution progressed, factories emitted large amounts of smoke and soot, which settled on the bark of the white birch trees. Originally, the white moths blended seamlessly with the white bark, providing them with a significant survival advantage against predatory birds. However, as the trees became darker, the white moths' camouflage was compromised. This shift in the environment directly impacted the survival rates of the moth population.

### Natural Selection
The concept of "survival of the fittest" describes how certain traits become more prevalent in a population when they confer a survival advantage. In this case, the white moths’ coloration was no longer advantageous. Predatory birds could easily spot and consume the white moths against the soot-darkened trees. Consequently, the moths that possessed greater amounts of gray pigmentation—those that already had spots—found themselves less visible against the newly darkened bark.

### Adaptation
Over successive generations, the moths with more gray pigmentation were more likely to survive and reproduce. This process is called natural selection, wherein the genes responsible for darker coloration became more common in the population. As the more camouflaged gray moths survived longer, they reproduced and passed on their traits to their offspring.

The moths underwent a gradual color shift as alleles for gray coloration became favored. Genetic variation within the population allowed for some moths to possess more gray pigmentation, enhancing their camouflage. Through this dynamic interaction of environment and selection pressure, the population's overall coloration shifted toward gray.

### Conclusion
Eventually, the moth population adapted to the new environmental conditions created by industrial pollution. This adaptation highlights the impact of environmental changes on species and how natural selection drives evolutionary changes in response to those changes. As the white birch trees became predominantly gray due to soot accumulation, the population of moths evolved to become more gray, demonstrating a significant case of adaptation and survival of the fittest in action. This scenario underscores the ecological principle that organisms must continually adapt to their changing environments in order to thrive.