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Section 16.3 - Natural Selection
An adaptation is an inherited characteristic that helps an organism survive and reproduce in its environment. Over time, adaptations become more common in the population. For example, suppose that the water in a pond gets darker over a period of four years. The table below shows what might happen to a frog population living in the pond.
Look at the pictures showing how a population of frogs changed over time.
Year 1
Year 2
Year 3
Year 4
Complete the table.
Year / Light-Colored Frogs / Dark-Colored Frogs1
2
3
4
Use the table to answer the question.
1. How did the numbers of light- and dark-colored frogs change over time?
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Section 16.4 - Evidence for Evolution
Use the words below and your knowledge of the evidence for evolution to complete the table. The first one has been done for you.
fossil recordgeographic distribution of living species
similarities in embryo development
Type of Evidence / What It Reveals
homologous body structures / Animals with different limb structures that develop from the same embryonic tissues evolved from a common ancestor.
Vertebrates share a common ancestor, asshown by how these organisms develop.
Intermediate forms show that organisms have evolved over time.
Species have adapted over time to local conditions.
Answer the question.
1. Give an example of homologous body structures.
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Section 17.1 - Gene Pools
A homozygous black mouse has two alleles for black fur. A heterozygous black mouse has one allele for black fur and one
allele for brown fur. A homozygous brown mouse has two alleles
for brown fur.
Sample Population
12 individuals
heterozygous
black
9 individuals
homozygous
brown
Each rectangle represents one mouse. Each mouse has two alleles, represented by circles, for fur color. Use the graph to color the gene pool of the sample population. Color alleles for black fur black and alleles for brown fur brown.
Gene Pool
Use the diagram to answer the questions.
1.How many black alleles are in the gene pool?
2.How many brown alleles are in the gene pool?
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Section 17.2 - Directional Selection
A population of birds eats seeds. Small seeds can be eaten by birds with small beaks. Larger, thicker seeds can be eaten only by birds with larger, thicker beaks. Suppose there is a shortage of small seeds but that there are still many large seeds.
Draw a new curve on the graph to show how the distribution of beak sizes might change as a result of selection in this environment.
Beak Size
Use the graph to answer the questions.
1.Which birds in this population have the highest fitness?
Circle the best answer.
small-beaked birds large-beaked birds
2.Explain how natural selection could lead to the change
you predicted.
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Section 17.2 - Stabilizing and Disruptive Selection
In most populations, a trait that has higher fitness leads to greater numbers of organisms with that trait. On the graphs, dotted lines represent the original population. The solid lines represent the population after selection has taken place.
Identify whether each graph shows stabilizing selection or disruptive selection. Write the type of selection shown below each graph.
original population
original population
Beak Size
Birth Weight
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Section 17.3 - Galápagos Island Finches
Finches in the Galápagos Islands have beaks adapted to eat the foods available in the birds’ habitats.
Use the words below to match each finch with the food it is adapted to eat. The first one is done for you.
Insects that live inside dead wood Large, thick-shelled seeds
Small seeds
Shape of Head and Beak
Main Food
Feeding Adaptation
Parrotlike beak
Uses cactus spines
Large crushing beak
Habitat
Trees
Trees
Ground
Ground
Pointed crushing beak
Use the table to answer the questions.
1.How does the large crushing beak help the fourth finch survive?
2.Circle the finch that would be least likely to survive if the insect population decreased.
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Section 17.3 - Speciation
Use the words below to identify each process that leads to speciation. One row has been completed for you.
Changes in the gene poolGeographic isolation
Ecological competitionReproductive isolation
Process / How It Leads to SpeciationFounders arrive / A population arrives in a new place.
Populations are separated by a geographic barrier and do not share a gene pool.
Populations evolve new traits in response to natural selection in their environments.
Populations reproduce only within their own group, leading to the development of new species.
Species evolve in a way that reduces competition between them.
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Section 19.1 - Relative Age
Sedimentary rock layers form in order by age. The oldest layers are on the bottom, and more recent layers lie above them in the order in which they formed.
Number the rock layers in the order that they formed. The first one has been done for you.
Use the diagram of the rock layers to number the fossils in order. The oldest fossil, labeled 1, has been done for you.
1
Use the diagram to answer the question.
1. Suppose that you found a fossil of the same species as fossil 1 in a rock layer in another location. What could you conclude about that rock layer?
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Evolution of Multicellular Life
Use the words below to fill in examples of life-forms that existed in each
period. Then, mark an X at two times when mass extinctions occurred.
early birdsreptiles and giant ferns
early human ancestorstrilobites and worms
first land plantsTyrannosaurus rex
Era / Period(s) / Life-formsCenozoic / Quaternary
Tertiary / whales and dolphins
Mesozoic / Cretaceous
Jurassic
Triassic / first dinosaurs and small mammals
Paleozoic / Permian and
Carboniferous
Devonian / insects, fishes, first amphibians
Silurian and
Ordovician
Cambrian
Precambrian
Time / Vendian / soft-bodied prokaryotes
and eukaryotes
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Adaptive Radiation
The diagram shows the evolutionary relationships between some
mammals. The dotted lines and question marks show places
where scientists are not sure when groups of animals branched
from earlier groups.
Follow the prompts.
•Color the group most closely related to the sirenians blue.
•Color the group most closely related to cetaceans yellow.
Ancestral Mammal
Use the diagram to answer the questions.
1.What is adaptive radiation?
2.Why are scientists not sure of all the evolutionary relationships
shown in the diagram above?
3.Which two groups are least closely related to artiodactyls?
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Punctuated Equilibrium
The theory of punctuated equilibrium is one explanation of how
evolution occurs. It describes a pattern of long periods of stability
interrupted, or punctuated, by shorter periods of rapid evolution.
The diagram shows one possible model for the evolution of horses
that follows this theory.
Look at the four circled areas. Put a check mark next to the circled areas
that show periods of rapid evolution. Put an X next to the circled areas
that show a relatively stable period.
Use the diagram to answer the question.
1. What on the diagram indicates that rapid evolution was
taking place?