Natural Selection Pre Assessment

Scientists measured the beak length of a population of birds in a lake in 1960. They measured the beak length of the bird population again in 2010. When was there more variation in the beak lengths of the birds by the lake?

• There was the same amount of variation in 1960 and in 2010.

• These bar graphs do not show the amount of variation in the population.

• There was more variation in 2010.

• There was more variation in 1960.

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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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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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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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Tree squirrels can have different fur colors. Squirrels live in forests where foxes also live. Foxes hunt squirrels for food. Squirrels that have fur that is the same color as the trees are harder for the foxes to see and catch. The diagram below shows a population of squirrels that live in a forest. At time 1, the population had the same number of black and gray squirrels. At time 2, after many generations, there were many more black squirrels and fewer gray squirrels 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 squirrels passed on the gene for black fur to their offspring.

• There were more black trees. Squirrels with black fur are more likely to survive, so the squirrels with gray fur changed to have black fur.

• There were more black trees. Squirrels with black fur are more likely to survive, so both types of squirrels passed on the gene for black fur to their offspring.

• There were more black trees. With each generation, more squirrels with black fur survived long enough to pass on the gene for black fur to their offspring.

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Blue jays are birds that live in the forest. They can have thick beaks, medium beaks, or thin beaks. 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. The population of blue jays shown above lives in an environment that has always had seeds with hard shells. Could there ever have been blue jays with thin beaks in this population?

• No blue jays could have been born with a thin-beak trait because none of the adult blue jays had that trait to pass down.

• No blue jays could have been born with a thin-beak trait in the past, but some with that trait could be born in the future if the environment changes to have pine cones with seeds.

• A blue jay could have been born with a mutation in its genes for the thin-beak trait and lived for a little while, but it would have been more likely to die before it had offspring.

• A blue jay could have been born with a mutation in its genes for the thin-beak trait, but having a mutation in its genes would have caused it to die when it was born.

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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 close to squirrels and catching them. The diagrams below show three possible fox populations. If their environment changes to have only brown dirt, which of the following fox 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 foxes will change the color of their fur if they need to.

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