Bernard Kettlewell, a British biologist, conducted a series of experiments in the 1950s to test his hypothesis on the evolution of melanism in the peppered moth. The peppered moth, Biston betularia, had undergone a significant change in its population dynamics, with the emergence of a dark-colored morph, Biston betularia carbonaria, in response to the industrial revolution. Kettlewell's hypothesis was that the increase in dark-colored moths was due to the selective advantage they gained from blending in with the dark tree trunks, which had become more prevalent due to pollution.
Designing the Experiment
Kettlewell designed an experiment to test his hypothesis, which involved releasing light-colored and dark-colored moths in both polluted and non-polluted areas. He chose two locations: one in Birmingham, which was heavily polluted, and another in Dorset, which was relatively pristine. Kettlewell marked and released a total of 480 moths, consisting of 240 light-colored and 240 dark-colored individuals, in each location.
Methodology and Data Collection
The moths were released in the morning, and Kettlewell used a team of observers to record the number of moths that were preyed upon by birds. The observers used binoculars to watch the moths from a distance, taking note of the time and the location of each predation event. Kettlewell also collected data on the number of moths that were recovered, either alive or dead, to determine the survival rates of each morph.
| Location | Light-Colored Moths | Dark-Colored Moths |
|---|---|---|
| Birmingham | 63 (26.25% survival rate) | 187 (77.92% survival rate) |
| Dorset | 154 (64.17% survival rate) | 41 (17.08% survival rate) |
Results and Analysis
Kettlewell’s results showed that in the polluted area of Birmingham, the dark-colored moths had a significantly higher survival rate (77.92%) compared to the light-colored moths (26.25%). In contrast, in the non-polluted area of Dorset, the light-colored moths had a higher survival rate (64.17%) compared to the dark-colored moths (17.08%). These findings supported Kettlewell’s hypothesis that the increase in dark-colored moths was due to the selective advantage they gained from blending in with the dark tree trunks in polluted areas.
Implications and Criticisms
Kettlewell’s experiment was a landmark study in the field of evolutionary biology, providing evidence for the role of natural selection in driving the evolution of melanism in the peppered moth. However, the study has also been subject to criticisms and controversies, with some arguing that the experiment was flawed due to the use of marked moths, which may have affected their behavior and survival rates. Additionally, some have questioned the assumption that the moths were resting on tree trunks during the day, which may not be the case in natural populations.
Key Points
- Kettlewell's experiment tested the hypothesis that the increase in dark-colored moths was due to the selective advantage they gained from blending in with dark tree trunks in polluted areas.
- The experiment involved releasing light-colored and dark-colored moths in both polluted and non-polluted areas and recording the number of moths that were preyed upon by birds.
- The results showed a significant difference in the survival rates of light-colored and dark-colored moths in polluted and non-polluted areas, supporting Kettlewell's hypothesis.
- The study has been subject to criticisms and controversies, including the use of marked moths and the assumption that moths rest on tree trunks during the day.
- Kettlewell's experiment remains a significant contribution to the field of evolutionary biology, providing evidence for the role of natural selection in driving the evolution of melanism in the peppered moth.
What was the main hypothesis tested by Kettlewell’s experiment?
+Kettlewell’s hypothesis was that the increase in dark-colored moths was due to the selective advantage they gained from blending in with the dark tree trunks in polluted areas.
What were the results of Kettlewell’s experiment?
+The results showed a significant difference in the survival rates of light-colored and dark-colored moths in polluted and non-polluted areas, supporting Kettlewell’s hypothesis.
What were some of the criticisms of Kettlewell’s experiment?
+Some of the criticisms of Kettlewell’s experiment include the use of marked moths, which may have affected their behavior and survival rates, and the assumption that moths rest on tree trunks during the day, which may not be the case in natural populations.