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7.2 Natural Selection

3 min readjanuary 2, 2023

Samantha Himegarner

Samantha Himegarner

Jillian Holbrook

Jillian Holbrook

Samantha Himegarner

Samantha Himegarner

Jillian Holbrook

Jillian Holbrook

is a process that occurs in nature whereby organisms that are better adapted to their environment are more likely to survive and reproduce. Essentially, lead to . As environments change, favors organisms with that have increased . This process helps to shape the characteristics of a population over time and can lead to the evolution of new species.

Phenotypic Variation

Just to recap: we know that can change the phenotypic ratios of a population in order to make them stronger. That is great! But what does it mean? 

A is an observable trait of any individual. For example, a human’s hair or eye color is a .

Each population will have a variety of individual phenotypes known as phenotypic variations. For example, while blonde and brown hair types seem to be more common, there is a for red hair in humans as well. While hair color does not necessarily aid in our general survival skills, there are specific phenotypes in nature that do allow for advantages in certain populations. In our camouflage example, let’s look at .

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2Fraphi-see-R-jWYWbOf88-unsplash.jpg?alt=media&token=ef3d110b-2f10-4432-a32b-3a0d712052f7

Image courtesy of Unsplash.

Peppered Moths

Originally, were white with some black speckles on their wings, which helped them blend into their environment. The light form of the peppered moth was less visible against the light-colored lichens and trees that were common in rural areas in England during the early 19th century. However, after the , soot-darkened trees in industrialized areas made the light visible to bird predators.

Due to a (random) , an individual in the population had completely dark wings. In the new environment, this dark form of the peppered moth now blended into the trees covered in soot, leading to an increase in fitness. With higher fitness, the dark form of the peppered moth had an increased likelihood to survive and reproduce, passing on the heritable trait of to its offspring. Over time, the population adapted to the industrialized environment through an increase in the for darker coloring in industrialized areas.

The story of the peppered moth is an excellent example of and how selective environmental pressures can influence the evolution of a species. As the dark form of the peppered moth survived to reproduce, it passed its "dark-coloring" gene onto its offspring in a pattern that continued until the population changed almost entirely. However, had the environment not changed, the mutated dark peppered moth most likely would have died, as well as any offspring, and the would not have taken over the population.

Through evolution by , the frequency of different traits in a population can change over time as species shift with the environments they live in!

Key Terms to Review (14)

Natural Selection

: Natural selection is the process by which species adapt to their environment. It's a key mechanism of evolution where traits that enhance survival and reproduction become more common in successive generations.

Heritable Variations

: Heritable variations refer to differences in genetic material that can be passed from parents to offspring through genes.

Differential Reproductive Success

: Differential reproductive success refers to the greater chance of survival and reproduction for organisms with traits advantageous for their environment, leading to these traits becoming more common in the population.

Selective Pressure

: Selective pressure is an environmental factor that causes a particular trait to become either more or less common in a population due to its impact on the survival or reproduction of individuals.

Adaptations

: Adaptations are traits that improve an organism’s chances of survival and reproduction in its natural habitat.

Fitness Benefits

: Fitness benefits refer to the advantages gained from certain traits or behaviors that increase an organism’s chances of survival and reproduction.

Phenotype

: A phenotype is the set of observable characteristics or traits of an organism resulting from the interaction of its genotype with the environment.

Phenotypic Variation

: Phenotypic variation refers to the differences in physical traits among individuals of the same species due to genetic and environmental factors.

Peppered Moths

: Peppered moths are a species known for their color variation from light to dark. This trait has been studied extensively as an example of natural selection where darker moths became more common during industrial pollution because they were better camouflaged against predators.

Allele Frequency

: Allele frequency refers to how often an allele appears in a population. It's usually given as a percentage.

Industrial Revolution

: The Industrial Revolution refers to a period of rapid technological and industrial growth that occurred during the 18th and 19th centuries. It's not directly a biological term, but it has significant implications for biology because it led to changes in human population size, distribution, and lifestyle.

Mutation

: A mutation is a change that occurs in our DNA sequence, either due to errors when the DNA is copied or as the result of environmental factors such as UV light and cigarette smoke.

Evolution of Species

: The evolution of species refers to changes in heritable traits within populations over successive generations, leading eventually to new species' formation from common ancestors.

Dark Coloring

: Dark coloring is a type of pigmentation that occurs in many species as a result of genetic variation and environmental adaptation. It often serves as a survival mechanism, aiding in camouflage or attracting mates.

7.2 Natural Selection

3 min readjanuary 2, 2023

Samantha Himegarner

Samantha Himegarner

Jillian Holbrook

Jillian Holbrook

Samantha Himegarner

Samantha Himegarner

Jillian Holbrook

Jillian Holbrook

is a process that occurs in nature whereby organisms that are better adapted to their environment are more likely to survive and reproduce. Essentially, lead to . As environments change, favors organisms with that have increased . This process helps to shape the characteristics of a population over time and can lead to the evolution of new species.

Phenotypic Variation

Just to recap: we know that can change the phenotypic ratios of a population in order to make them stronger. That is great! But what does it mean? 

A is an observable trait of any individual. For example, a human’s hair or eye color is a .

Each population will have a variety of individual phenotypes known as phenotypic variations. For example, while blonde and brown hair types seem to be more common, there is a for red hair in humans as well. While hair color does not necessarily aid in our general survival skills, there are specific phenotypes in nature that do allow for advantages in certain populations. In our camouflage example, let’s look at .

https://firebasestorage.googleapis.com/v0/b/fiveable-92889.appspot.com/o/images%2Fraphi-see-R-jWYWbOf88-unsplash.jpg?alt=media&token=ef3d110b-2f10-4432-a32b-3a0d712052f7

Image courtesy of Unsplash.

Peppered Moths

Originally, were white with some black speckles on their wings, which helped them blend into their environment. The light form of the peppered moth was less visible against the light-colored lichens and trees that were common in rural areas in England during the early 19th century. However, after the , soot-darkened trees in industrialized areas made the light visible to bird predators.

Due to a (random) , an individual in the population had completely dark wings. In the new environment, this dark form of the peppered moth now blended into the trees covered in soot, leading to an increase in fitness. With higher fitness, the dark form of the peppered moth had an increased likelihood to survive and reproduce, passing on the heritable trait of to its offspring. Over time, the population adapted to the industrialized environment through an increase in the for darker coloring in industrialized areas.

The story of the peppered moth is an excellent example of and how selective environmental pressures can influence the evolution of a species. As the dark form of the peppered moth survived to reproduce, it passed its "dark-coloring" gene onto its offspring in a pattern that continued until the population changed almost entirely. However, had the environment not changed, the mutated dark peppered moth most likely would have died, as well as any offspring, and the would not have taken over the population.

Through evolution by , the frequency of different traits in a population can change over time as species shift with the environments they live in!

Key Terms to Review (14)

Natural Selection

: Natural selection is the process by which species adapt to their environment. It's a key mechanism of evolution where traits that enhance survival and reproduction become more common in successive generations.

Heritable Variations

: Heritable variations refer to differences in genetic material that can be passed from parents to offspring through genes.

Differential Reproductive Success

: Differential reproductive success refers to the greater chance of survival and reproduction for organisms with traits advantageous for their environment, leading to these traits becoming more common in the population.

Selective Pressure

: Selective pressure is an environmental factor that causes a particular trait to become either more or less common in a population due to its impact on the survival or reproduction of individuals.

Adaptations

: Adaptations are traits that improve an organism’s chances of survival and reproduction in its natural habitat.

Fitness Benefits

: Fitness benefits refer to the advantages gained from certain traits or behaviors that increase an organism’s chances of survival and reproduction.

Phenotype

: A phenotype is the set of observable characteristics or traits of an organism resulting from the interaction of its genotype with the environment.

Phenotypic Variation

: Phenotypic variation refers to the differences in physical traits among individuals of the same species due to genetic and environmental factors.

Peppered Moths

: Peppered moths are a species known for their color variation from light to dark. This trait has been studied extensively as an example of natural selection where darker moths became more common during industrial pollution because they were better camouflaged against predators.

Allele Frequency

: Allele frequency refers to how often an allele appears in a population. It's usually given as a percentage.

Industrial Revolution

: The Industrial Revolution refers to a period of rapid technological and industrial growth that occurred during the 18th and 19th centuries. It's not directly a biological term, but it has significant implications for biology because it led to changes in human population size, distribution, and lifestyle.

Mutation

: A mutation is a change that occurs in our DNA sequence, either due to errors when the DNA is copied or as the result of environmental factors such as UV light and cigarette smoke.

Evolution of Species

: The evolution of species refers to changes in heritable traits within populations over successive generations, leading eventually to new species' formation from common ancestors.

Dark Coloring

: Dark coloring is a type of pigmentation that occurs in many species as a result of genetic variation and environmental adaptation. It often serves as a survival mechanism, aiding in camouflage or attracting mates.