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Name: Rachael
Status: student
Grade: 9-12
Location: IL
Country: USA
Date: Spring 2013

I am working on Natural selection in Biology. I am working with a population of frogs. Over a 4 year period the frogs went from a light color to all dark in color. I need to describe a possible scenario that would have caused this. Would it be because the frogs needed to adapt to their environment and became dark in color to hide from their predators.


Did you separate your frogs into color categories and then mate them to produce off spring of same color? (This is called Selective Breeding)

Another mechanism is survival of the fittest, but you didn’t say anything about the presence of predators that would select out frogs of a light color leaving darker color frogs to survive and pass on their dark genes.

And you didn’t mention your environment. Were your frogs in a light or dark container? There might be an adaptation mechanism going on, like in chameleons.

Are all of your frogs of the same species?

Epigenetics may be playing a role here. If all of your frogs are of the same species and have essentially the same DNA configurations, epigenetics is the means of turning on or turning off the expression of genes (like skin color). Epigenetics mechanisms respond to environmental factors such as levels of nutrition, levels of stress, and other environmental influences that may generate froggy hormones.

Sincere regards, Mike Stewart

Individual organisms can't evolve-it's only the populations that evolve. A single frog won't go from being light to being dark in their lifetime (unless that is already part of their genome-ie chameleons can change to match their background). So saying that "frogs adapted because they needed to" is referred to as LaMarckian language (google LaMarck and evolution). IF the darker frogs survive better than the light ones for some reason that could be due to natural selection. Then, we look into what might be the selective pressure. It could be any of the things you mention. BUT, if you have a very small population, the allele frequencies could have changed due to genetic drift. Genetic drift is an accidental (random) loss of alleles due to the population being small.


Hi Rachael,

Thanks for the question. Yes, you have a possible explanation for the observed changed. Please note that there are many possibl explanations for the same type of change.

I hope this helps. Please let me know if you have more questions. Thanks Jeff

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