Selection and Speciation

How can changes in a population result in the formation of a new species?

Have you ever wondered how the great diversity of life on Earth has come about or how a single new species forms? Environmental pressures may cause populations to change over time or evolve. This is because an organisms ability to live to adulthood in its current environment will determine its reproductive success and ability to pass on its genes. But changes within a population can occur without creating a new species. At what point do scientists start thinking of a new name for a species?

Watch this short video on types of natural selection

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What variables do the graphs in Model 1 compare?

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What are the three types of selection shown in the graphs? Type the 3 names with a comma between

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According to the graphs in Model 1, there is variation in the body mass in the original population. Using your knowledge of genetics, describe how this variation is possible. Why is there variation in a population even before selection.

Refer to Graph A

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How is the population that has experienced selection different from the original population?

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Fitness is defined as the relative ability of an individual (or population) to survive, reproduce, and pass on genes. Which individuals in the original population appear to display better fitness?

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As a group, propose some characteristics of the environment that could lead to the population changes illustrated in graph A.

Refer to graph B

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How is the population that has experienced selection different from the original population?

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Fitness is defined as the relative ability of an individual (or population) to survive, reproduce, and pass on genes. Which individuals in the original population appear to display better fitness?

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As a group, propose some characteristics of the environment that could lead to the population changes illustrated in graph B.

Refer to graph C

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How is the population that has experienced selection different from the original population?

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Fitness is defined as the relative ability of an individual (or population) to survive, reproduce, and pass on genes. Which individuals in the original population appear to display better fitness?

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As a group, propose some characteristics of the environment that could lead to the population changes illustrated in graph C.

Match each of the following scenarios with the graph showing the type of selection that would occur

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This is:

Directional Selection

Disruptive Selection

Stabilizing Selection

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Explain your answer

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This is:

Directional Selection

Stabilizing Selection

Disruptive Selection

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Explain your answer

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This is:

Stabilizing Selection

Directional Selection

Disruptive Selection

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Explain your answer

Natural selection, the improved fitness of certain individuals in the population that allows for survival and reproduction, is the primary mechanism by which populations change over time.

But at what point does a change in the population develop a new species?

Data have been collected showing that the average height of an American adult is increasing, but that does not mean the American population has evolved into a new species.

The following image describes what it means for organisms to be members of the same species, or not.

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Consider all of the pairs of organisms in Model 2 that are not of the same species. What criterion are missing in all cases that could be used to define a species?

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Could directional selection lead to the creation of a new species? Justify your reasoning using what you've learned from this activity. Provide a possible example or scenario.