Descent with Modification Video Lessons

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Problem: Cliff swallows are birds that often build nests under a highway overpass or on a bridge, they are very common on MO and KS roads.Swallows build nests from mud, and the edges between the horizontal overpass and vertical walls are ideal locations for their nests. Unfortunately, these locations also make cliff swallows vulnerable to being hit by cars and trucks.The graph below shows the data collected on the shape and length of the cliff swallows' wings.The graph compares the wing length data collected from cliff swallows that were killed on the roads (blue bars) and from cliff swallows in the general population (maroon bars). Analyze the data in the graph and use it to complete the sentences below.Drag the terms below to the appropriate blanks on the right to complete the sentences.Natural selection          Increased          DecreasedShorter          Longer          Adaptation1. From 1984 to 2012, the wing length of cliff swallows in the general population generally _____.2. During the same time period, the wing length of cliff swallows killed on the roads generally _____.3. In most years where data was collected, the wings of cliff swallows killed on the roads were _____ than the wings of swallows found in the population at large.4. Shorter wings allow cliff swallows to take off from the ground more vertically, enabling them to better avoid oncoming cars. As a result, cliff swallows in populations near highways with _____ wings have a survival advantage.5. The data suggest that, over time, _____ resulted in the evolution of shorter wings in the cliff swallow population.6. Shorter wings are a(n) _____ in this population.

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Problem Details

Cliff swallows are birds that often build nests under a highway overpass or on a bridge, they are very common on MO and KS roads.

Swallows build nests from mud, and the edges between the horizontal overpass and vertical walls are ideal locations for their nests. Unfortunately, these locations also make cliff swallows vulnerable to being hit by cars and trucks.

The graph below shows the data collected on the shape and length of the cliff swallows' wings.

The graph compares the wing length data collected from cliff swallows that were killed on the roads (blue bars) and from cliff swallows in the general population (maroon bars). Analyze the data in the graph and use it to complete the sentences below.


Drag the terms below to the appropriate blanks on the right to complete the sentences.

Natural selection          Increased          Decreased

Shorter          Longer          Adaptation


1. From 1984 to 2012, the wing length of cliff swallows in the general population generally _____.

2. During the same time period, the wing length of cliff swallows killed on the roads generally _____.

3. In most years where data was collected, the wings of cliff swallows killed on the roads were _____ than the wings of swallows found in the population at large.

4. Shorter wings allow cliff swallows to take off from the ground more vertically, enabling them to better avoid oncoming cars. As a result, cliff swallows in populations near highways with _____ wings have a survival advantage.

5. The data suggest that, over time, _____ resulted in the evolution of shorter wings in the cliff swallow population.

6. Shorter wings are a(n) _____ in this population.

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