Natural Selection

By: Khushi Gupta

Image by Gordon Johnson on Pixabay

Everyone has heard a version of “survival of the fittest” sometime over the course of their lives. It’s just another term that our society has come to know. But where did that phrase originate from, and is it even true? Charles Darwin, an English scientist, is known commonly for his advancements and contributions to the science of evolution.

Evolution is the process of advancements over time, and Darwin associated natural selection to this process. Natural selection is the idea that helpful traits are passed down to generations as they are better equipped to handle environmental changes.

Take this experiment as an example, where scientists observed light and dark colored pocket mice in different habitats. Scientists finally concluded that differences in fur color in the population of rock pocket mice were caused by natural selection and genetic mutations.

In the beginning, the area that the light-colored rock pocket mice lived in was an area of light-colored desert sands with the population of light-colored mice to dark colors being 10 to 2. Due to volcanic activity occurrences, dark patches of volcanic rock formed where these mice lived. Over time, the light-colored mice population decreased while a new population of dark-colored mice steadily rose. The rate of light to dark mice became 9 to 3. The numbers changed to an even ratio with 6 light-colored and 6 dark-colored mice. The most recent count of the mice showed that the dark-colored mice population was significantly greater than the light mice with a ratio of 2 to 10.

This location of dark volcanic rock made the light-colored mice stand out from their surroundings. Most of the mice’s predators are visual predators, decreasing the survival chance of the light-colored mice as they can easily be spotted from the dark backgrounds. Over time, the light-colored mice population decreased as a result of being easy prey, while the dark-colored mice, a mutation, increased. The mutation in the mouse changes its phenotype and eventually spreads to the entire population as it makes the survival rates/fitness of the organism increase. This is formed when the DNA is incorrectly base paired with the mRNA from either deletions, insertions, and/or base substitutions during transcription. In translation, the changes in the mRNA lead to a domino effect of differences in the ribosomes, pairings with the tRNA, and amino acids that lead to a different protein created from the light skinned mice. One change is that the MC1R protein, a protein that affects fur color, would become active, producing dark colored fur.

The MC1R protein affects the mice’s fur color as it is located in the melanocytes (pigment-producing cells) of the cell membrane. The MC1R protein’s mutation causes the gene to produce more eumelanin causing the mice to have a darker pigment of fur. Without the mutation, the melanocytes produce more pheomelanin than eumelanin, making the mice have light-colored fur. The mice’s predators mainly depend on sight to catch their prey, highlighting the importance of the mice’s fur color. Light-colored mice are able to survive as they camouflage into the sand, but in a dark lava environment, they are less likely to survive as they stand out from their surroundings. The opposite is true for dark colored mice. The change in color occurred as the light colored mice were easily spotted, making the dark fur trait more desirable as it helped them camouflage with the dark lava. Frequencies of alleles that affect fur color are different in populations based on whether the mice live in a light or dark background. Allele 2 causes the mice to have a darker fur color, which is useful if the mice live in a darker background as it gives them a competitive advantage over light furred mice. Natural selection makes it so that desirable traits are more likely to get passed down while the traits that give the organisms a disadvantage are less likely. This can be seen as the dark fur causes mice to blend in, giving them a longer lifespan in which they are more likely to reproduce and increase the mouse population while the light mice will die quicker and be less likely to reproduce. This is also known as survival of the fittest. Genetic changes like allele 2 that gives the organism better survival rates are passed down from parent to offspring. Over time, the entire population can contain this allele, as observed where 100% of the lava west mice population has allele 2.

If environmental conditions remain overall the same with no major changes, it can be assumed that this trend will continue for the next century. The dark-colored genotype would become the dominant trait with the light-colored trait being recessive, so the phenotype would not completely cease to exist. This means that the overall population of pocket mice would be dark-colored with the minority having light-colored fur. With a sample space of 12 mice, 11 out of the 12 would be dark colored with only one being light colored.

Educational Content:

Q. What is natural selection?

A: The process where organisms that have better traits have better survival and reproduction rates that then get passed down to their offspring.

Q: Who came up with the theory of natural selection?

A: Charles Darwin

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