Natural Selection Pre Assessment

Scientists measured the spot size of guppies (small fish) in two different populations. Which population has more guppies with large spots?

• They both have the same number of guppies with large spots.

• The population in Brazil has more guppies with large spots.

• The population in Venezuela has more guppies with large spots.

• These bar graphs do not show which population has more guppies with large spots.

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Hummingbirds can have different beak 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 diagrams below show three possible hummingbird populations.

If their environment changes to have only long flowers, which of the following hummingbird populations will most likely survive?

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

• All the populations will survive because the hummingbirds will change the length of their beaks if they need to.

• Populations 1 and 2 will survive.

• Populations 2 and 3 will survive.

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Eider ducks live in the ocean and have a layer of warm feathers underneath their regular feathers. They can have feathers of different thicknesses.

These feathers help the ducks stay warm in cold water. Ducks with thicker feathers are more likely to stay warm and survive in cold water. But, in warm water, thicker feathers can make the ducks overheat and die.

The diagram below shows a population of ducks that live in an area of an ocean. At time 1, the population had the same number of ducks with thin and thick feather layers. At time 2, after many generations, there were many more ducks with a thin feather layer and fewer ducks in the population with a thick feather layer.

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 ducks passed on the gene for thin feathers to their offspring.

• The water became warm. As a result, ducks with thin feathers were more likely to survive, so the ducks with thick feathers changed to have thin feathers.

• The water became warm. With each generation, more ducks with thin feathers survived long enough to pass on the gene for thin feathers to their offspring.

• The water became warm. As a result, ducks with thin feathers were more likely to survive, so both kinds of ducks passed on the gene for thin feathers to their offspring.

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There is a kind of snake that can be born with red, yellow, or green skin. Eagles hunt these snakes, but snakes that are the same color as their environment are harder for the eagles to see and catch.

A population of snakes once lived in an environment where there was sand and dirt, but no grass. The image above shows what the population looked like then. The environment changed so that green grasses and plants now grow there.

The diagrams below show two predictions for what the population could look 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 yellow or red snakes had a baby with a mutation in its genes for the green-skin trait. Because green snakes are more likely to survive, that baby survived long enough to pass on its mutation, so the green trait became more common over generations.

• Prediction 1 is best. Green snakes are more likely to survive, so yellow and red snakes began to have offspring with mutations in their genes for the green-skin trait so that their offspring would have a better chance of surviving.

• Prediction 2 is best. A snake could have been born with a mutation in its genes for the green-skin trait and lived for a little while. Because green snakes are more likely to die, it would have been more likely to die before it had offspring, so the final population will only have yellow and red snakes.

• Prediction 2 is best. A snake could have been born with a mutation in its genes for the green-skin 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 yellow and red snakes.

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Scientists measured the height of the giraffes in two different populations. Which population has the largest number of tall giraffes?

• The population in Niger has the largest number of tall giraffes.

• The population in Somalia has the largest number of tall giraffes.

• Both populations have the same number of tall giraffes.

• These bar graphs do not show which population has more tall giraffes.  

Harbor seals live in northern oceans and have a layer of blubber (fat) that keeps them warm. Seals can have blubber of different thicknesses.

Seals with thicker blubber are more likely to stay warm and survive in cold ocean waters. But, in warm ocean waters, thicker blubber can make the seals overheat and die.

The diagrams below show three possible seal populations.

If their environment changes to have warm water, which of the following seal 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 seals will change the thickness of their blubber if they need to.

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Guppies are small fish that live in South American rivers. They can have different-sized spots on their bodies.

The river bottoms are covered in rocks. Guppies with spots that are the same size as the rocks on the bottom are harder for bigger fish to see and catch.

The diagram below shows a population of guppies that live in a river. At time 1, the population had the same number of guppies with small and large spots. At time 2, after many generations, there were many more guppies with small spots and fewer guppies with large spots 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 guppies passed on the gene for small spots to their offspring.

• The rocks became smaller. With each generation, more guppies with small spots survived long enough to pass on the gene for small spots to their offspring.

• The rocks became smaller. Guppies with small spots are more likely to survive, so the guppies with large spots changed to have small spots.

• The rocks became smaller. Guppies with small spots are more likely to survive, so both kinds of guppies passed on the gene for small spots to their offspring.

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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.

A population of foxes once lived in an environment where there was not very much snow. The image above shows what the population looked like then. The environment changed so it is now very snowy.

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 brown or gray foxes had a baby with a mutation in its genes for the white-fur trait. Because white foxes are more likely to survive, that baby survived long enough to pass on its mutation, so the white-fur trait became more common over generations.

• Prediction 1 is best. White foxes are more likely to survive, so brown and gray foxes began to have offspring with mutations in their genes for the white-fur trait so that their offspring would have a better chance of surviving.

• Prediction 2 is best. A fox could have been born with a mutation in its genes for the white-fur trait and lived for a little while. Because white foxes are more likely to die, it would have been more likely to die before it had offspring, so the final population will only have brown and gray foxes.

• Prediction 2 is best. A fox could have been born with a mutation in its genes for the white-fur 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 brown and gray foxes.

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Scientists measured the spine size of a population of cactuses found in an area in 1970. They measured the spine size of the cactus population again in 2015. Which of the statements below best describes the difference in the cactuses at the two time points?

• The cactuses in 1970 had smaller spines than the cactuses in 2015.

• The cactuses in 1970 had larger spines than the cactuses in 2015.

• There were more cactuses in 1970 than there were in 2015.

• There was more variation in spine size in 1970 than there was in 2015.

Brown anoles are lizards that live on islands in the Bahamas. They can have legs of different lengths.

Lizards with shorter legs are better at climbing trees than lizards with longer legs. This makes lizards with shorter legs better at escaping from the floods that sometimes cover the islands.

The diagrams below show three possible lizard populations.

If their environment changes so that there are many floods each year, which of the following lizard populations will most likely survive?

• All the populations will survive because the lizards will change the length of their legs if they need to.

• 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.

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