Natural Selection

Blue jays are birds that live in the forest. They can have beaks of different thicknesses.

Blue jays use their beaks to get to the seeds they eat. Blue jays with thinner beaks can easily reach and eat the seeds inside pinecones. Blue jays with thicker beaks can easily open and eat seeds with hard shells.

If their environment changes to have only seeds in pinecones, which of the following blue jay populations will most likely survive?

• Populations 1 and 2 will most likely survive.

• Populations 2 and 3 will most likely survive.

• Only Population 2 will survive because it is the only population with variation.

• All the populations will survive because the blue jays will change the thickness of their beaks if they need to.

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Northern foxes can have different fur colors.

The foxes hunt squirrels for food. Foxes that have fur the same color as their environment are better at getting closer to squirrels and catching them.

The diagram below shows a population of foxes that live in one area. At time 1, the population had the same number of brown and white foxes. At time 2, after many generations, there were many more brown foxes and fewer white foxes in the population.

How did the environment change between time 1 and time 2? How did the population change?

• You cannot tell how the environment changed. With each generation, more foxes passed on the gene for brown fur to their offspring.

• The environment became brown. Brown foxes are more likely to survive, so the white foxes changed to have brown fur.

• The environment became brown. Brown foxes are more likely to survive, so both kinds of foxes passed on the gene for brown fur to their offspring.

• The environment became brown. With each generation, more brown foxes survived long enough to pass on the gene for brown fur to their offspring.

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Hummingbirds can have beaks of different lengths.

They use their beaks to reach to the nectar (their food) at the bottom of flowers. Hummingbirds with longer beaks can get food from long flowers. Hummingbirds with shorter beaks cannot reach the nectar in long flowers. If a hummingbird can’t easily reach its food, it will die.The population of hummingbirds once lived in an environment where there were very few long or medium flowers. The image above shows what the population looked like then. The environment changed so that mostly long and medium flowers now grow there.

The diagrams below show two predictions for what the population could be like after many generations.

Which prediction best shows what the population could look like after many generations? What caused it to change?

• Prediction 1 is best. Two hummingbirds with short or medium beaks had a baby with a mutation in its genes for the long-beak trait. Because long-beak hummingbirds are more likely to survive, that baby survived long enough to pass on its mutation, so the long-beak trait became more common over generations.

• Prediction 1 is best. Hummingbirds with long beaks are more likely to survive, so hummingbirds with short and medium beaks began to have offspring with a mutation in its genes for the long-beak trait so that their offspring would have a better chance to survive.

• Prediction 2 is best. A hummingbird could have been born with a mutation in its genes for the long-beak trait and lived for a little while. Because long-beak hummingbirds are more likely to die, it would have been more likely to die before it had any offspring, so the final population will only have medium or short beak hummingbirds.

• Prediction 2 is best. A hummingbird could have been born with a mutation in its genes for the long-beak trait, but having a mutation in its genes would have caused it to die when it was born, so the final population will only have medium or short beak hummingbirds.

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Which two histograms show the same amount of variation?

• A and D

• B and C

• B and D

• A and C

Which histogram shows NO variation?

• A

• B

• C

• D

Which histogram shows a high variation?

• A

• B

• C

• D

In a freezing cold environment with no predators, a non-adaptive trait for ostrilopes would be:

• low fur levels

• low poison levels

• high fur levels

• high poison levels

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In a yellow (level 7) environment with predators, an adaptive trait for ostrilopes would be:

• Being yellow (level 7)

• Being blue (level 1)

• Being green (level 4)

• Being green (level 3)

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What is an adaptive trait?

• a trait that makes it less likely that an individual will survive in a specific environment

• a trait that makes it more likely that an individual will survive in a specific environment

• an instruction for making a protein molecule

• the number of individuals with each trait in a population

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Where do the genes that determine an individual's traits come from?

• An individual can be born with any genes, since genes are random.

• 
  Individuals grow genes specific to their environment.

• Parents pass their genes down to their offspring.

• Parents choose which genes their offspring have when each individual is born.

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