Table 1: Amount of Light/ Dark moths remaining before, during, after industrial revolution
| Tree Bark | # of Melanic Moths Remaining | # of Light Moths Remaining | % of Melanic Moths Remaining (/30) | % of Light Moths Remaining (/30) | |
| Light (Pre-Industrial Revolution) | 1 | 13 | 13 | 43% | 43% |
| 2 | 10 | 15 | 33% | 50% | |
| 3 | 8 | 16 | 27% | 53% | |
| 4 | 8 | 17 | 27% | 57% | |
| 5 | 5 | 19 | 17% | 63% | |
| Intermediate (Early Industrial Revolution) | 1 | 14 | 12 | 47% | 40% |
| 2 | 16 | 11 | 53% | 37% | |
| 3 | 15 | 10 | 50% | 33% | |
| 4 | 15 | 9 | 50% | 30% | |
| 5 | 15 | 8 | 50% | 27% | |
| Dark (Post- Industrial Revolution) | 1 | 15 | 14 | 50% | 46% |
| 2 | 16 | 12 | 53% | 40% | |
| 3 | 18 | 10 | 60% | 33% | |
| 4 | 20 | 8 | 67% | 26% | |
| 5 | 22 | 5 | 73% | 16% |
The light colored moths were most successful at avoiding predation in the pre-Industrial Revolution bark habitat; whereas the dark colored moths were most successful at avoiding predation during the post-industrial revolution bark habitat and during the early industrial period.
Based on my observations, natural selection of these moth populations definitely occurred. During the pre-industrial revolution, the bark color was lighter and the data confirms that a higher percentage of lighter colored moths remained; by the 5th generation 63% of the lighter colored moths remained while only 17% of the darker colored moths remained. Since it was advantageous for the moths to be of a lighter color during the pre-industrial revolution, natural selection allowed more of the light colored moths to survive. As the early industrial revolution began to set in, it became slightly more advantageous to be a darker moth and therefore there was a decline in the amount of lighter moths and the increase of darker moths remaining. Finally during the post- Industrial Revolution when tree bark was dark, it became a near absolute advantage to be a darker moth and the data confirms this, because during the 5th generation 73% of darker moths remained, while only 16% of lighter moths remained.
The purpose of using the intermediate tree bark background was to demonstrate the effect on the moths remaining when it was not necessarily advantageous to be a dark or light moth. This was supposed to act as a control test, allowing both moths colors to be susceptible to predation and demonstrate how their current adaptive camouflage would affect the percentage of them remaining under transitional circumstances.
For the most part, the data we ascertained from this experiment was quite accurate. It followed the trends which were expected; on lighter bark, lighter-coloured moths were prevalent, as the bark got darker (intermediate) the darker coloured moth began to be more prevalent and once the bark was dark, the darker coloured moth were clearly dominating the lighter coloured moth in percentage remaining after each generation. The potential for error in the lab lies mainly in the hands of the student playing the role of the predator. They need to objectively hunt the moths as if they were an animal predator; looking for the most noticeable moths before they consume the better camouflaged ones. If the predator student has a predisposition to attempt to hunt each moth species equally, it will skew the results and not provide an accurate representation of the % of remaining moths. Though, this intentional hunting didn’t occur with the results above, it is an important source of error that experimenters can be prone to during their simulation.
Since you begin with both 15 lighter colored and 15 melanic pepper moths, there is one primary suggestion that can be made to the methodology of this experiment. In step 6 of the procedure it tells the assistant to “replace each consumed light- coloured moth with a melanic moth, and each consumed melanic moth with a lighter-coloured moth”. This is not a fair representation of the actual procreation of each species of peppered moth. It would make much more sense to count out the remaining amount of each colour moth and then have the remainders of each colour moth reproduce according. So if there are 9 light-coloured moths, they would make 9 more moths and if there are 14 darker moths remaining, they will make 14 more dark moths. This is a more accurate representation of the amount of moths that will be created after each generation as oppose to assuming there would be a switch in colour after each moth type is consumed. Obviously to make this modification work, the time interval at which the predator has to hunt must be increased from the 4s to around 8-10s, to allow enough moths to be consumed so that visible declines or increases can be seen within the first 5 generations.
Unlike most frogs, the poison arrow/ dart species exhibit brightly-colored bodies (red, yellow, orange, blue etc.). These bright colours are relative to the toxicity of the particular frog species and they display aposematic patterns to warn off predators. These “warning colouration”, belong to a characteristic trait known as anti-predator adaptations. By not blending into their surrounding like traditional frogs would, they appear as unusually and offsetting to predators, like a warning signal showing the unprofitability of a poisonous frog to potential predators.
In 1809, Jean Baptiste Lamarck proposed the basic concepts outlining the evolution of species. Based on his observation of the physiological characteristics of organisms, he derived a relationship between the phenomenon of new species, or speciation: a species gradually accumulate new characters and eventually becomes a different species. Lamarck hypothesized that the adaptation of an animal to new conditions in which they live allows for it continued survival. The case of the pepper moth is in direct accordance with Lamarck’s position, because it shows the evolution of the lighter coloured pepper moth to a melanic pepper moth in order to prosper and continue surviving. This adaption was crucial for the moth to survive and it evolved from the less advantageous light pepper pattern to a melanic pepper pattern to do so.
If the pepper moth showed little variation and the evolution did not take place, it would be extremely endangered, if not extinct. Failure to adapt to a changing environment, especially something as critical as camouflage would definitely have a drastic negative effect on the peppered moth populace and most likely lead to its extinction.
The term industrial melanism refers to the genetic darkening of species in response to pollutants. The darkening or (melanisation) of a species population significantly increased the prospect that will be able to procreate and create descending generations that will be able to survive and garner protection from the available camouflage. It takes place as natural selection over the generations as the lighter, more conspicuous animals are eaten by predators. The most widespread example of such industrial melanism is during the Industrial Revolution where there was a widespread of pollution in Manchester, England and the trees which the peppered moths rested on became blackened with sooth. A genetic mutation, which resulted in Melanic Peppered moths flourishing because they were completely black and they were able to hide on the darkened trees.
Bibliography
The American Museum of Natural History. <http://research.amnh.org/herpetology/amphibia/names.php?taxon=&family=Dendrobatidae&subfamily=&genus=&commname=&authority=&year=&geo=0&dist=&comment=>. Retrieved 2010-06-09.
Young, M. (2003). Moonshine: Why the Peppered Moth Remains an Icon of Evolution.< http://www.talkreason.org/articles/moonshine.cfm>. Retrieved 2010-06-09.
Gould, Stephen Jay (2002). <http://www.britannica.com/The_Structure_of_Evolutionary_Theory>. Harvard: Belknap Harvard. Retrieved 2010-06-09.
