Name _____________________________________________________ Period _________ Date _____________
16.1 and 16.2
Lesson Objectives
State Charles Darwin’s contribution to science.
Describe the three patterns of biodiversity noted by Darwin.
Describe Lamarck’s hypothesis of evolution.
Explain the role of inherited variation in artificial selection.
Lesson Summary
Darwin’s Epic Journey Darwin developed a scientific theory to explain how evolution, or change over time, occurs in living things. Darwin’s theory explains how modern organisms have evolved over long periods of time through descent from common ancestors.
Observations Aboard the Beagle During his five-year trip on the Beagle, Darwin made many observations and collected a great deal of evidence.
He noticed that many different, yet ecologically similar, animal and plant species occupied different, yet ecologically similar, habitats around the globe.
On the Galápagos Islands, Darwin noticed that the traits of many organisms—such as the shell shapes of tortoises—varied from island to island. He noticed that different, yet related, animal and plant species occupied different habitats within a local area.
Darwin collected fossils, the preserved remains of ancient organisms. He noticed that some fossils of extinct species resembled living species.
Darwin’s findings led him to think that species are not fixed and that they could change by some natural process.
An Ancient, Changing Earth In Darwin’s day, most Europeans believed that Earth and all its life forms were only a few thousand years old and had not changed very much in that time. Several scientists who lived around the same time as Darwin began to challenge these ideas. These scientists had an important influence on the development of Darwin’s theory of evolution.
Knowing that Earth could change over time helped Darwin realize that species might change as well. Knowing that Earth was very old convinced Darwin that there had been enough time for life to evolve.
Lamarck’s Evolutionary Hypothesis Jean-Baptiste Lamarck was one of the first scientists to propose hypotheses about how evolution occurred.
To explain evolution, Lamarck hypothesized that all organisms have an inborn drive to become more complex and perfect. According to Lamarck, an organism could gain or lose traits during its lifetime by using or not using certain organs.
Lamarck also hypothesized that acquired characteristics could be passed on to an organism’s offspring leading to evolution of the species.
Scientists now know that most of Lamarck’s ideas about evolution are incorrect. However, he correctly suggested that life is not fixed and was the first to offer a natural and scientific explanation for evolution.
Further, he recognized that an organism’s traits are linked to its environment.
Artificial Selection Plant and animal breeders in Darwin’s time used a process now known as artificial selection to improve their crops and livestock. In artificial selection, nature provides the variations, and humans select those they find desirable. Darwin experimented with artificial selection. The results from his experiments indicated natural variation was very important because it provided the raw material for evolution.
1. How old is the Earth?
2. How did Lamarck propose that species change over time?
3. Define evolution.
Use the drawings of the tortoises to answer Question 4.
Isabela Island tortoise Hood Island tortoise
4. Given its body structure, which tortoise above would require a habitat where food is easy to reach?
5. Darwin observed that the birds on the Galapagos Islands that he would eventually discover were finches had differently shaped beaks. What might this suggest about the eating habits of the birds?
6. What did the similarities between fossil animals and modern animals, like the glyptodont and armadillo, suggest to Darwin?
7. Complete the graphic organizer by listing three ways that species vary. For each pattern of biodiversity, list an example.
vary
an example of which is an example of which is an example of which is Species
8. What is a fossil? How can they be used to study evolution?
16.3
Lesson Objectives
Describe the conditions under which natural selection occurs.
Explain the principle of common descent.
Lesson Summary
Evolution by Natural Selection Darwin published On the Origin of Species in 1859. In the book, Darwin describes and provides evidence for his explanation of how evolution occurs. He called this process natural selection because of its similarities to artificial selection. Darwin’s theory of evolution by natural selection can be summed up as follows:
More offspring are produced than can survive to reproduce. There is competition for limited resources, or a struggle for existence.
Individuals exhibit variation in their traits and some of these differences can be passed on to their offspring.
Inherited traits that increase an organism’s ability to survive and reproduce are called adaptations.
Differences among adaptations affect an individual’s fitness—the ability to survive and reproduce in a specific environment.
Only the fittest organisms live to reproduce and pass on their adaptive traits to offspring. This is known as the survival of the fittest.
From generation to generation, populations continue to evolve as they become better adapted, or as their environment changes.
Common Descent Darwin argued that all species are descended, with modification, from common
ancestors. Through descent with modification, all organisms—living and extinct— are linked on a single tree of life.
9. In artificial selection, __________________ provides the variation and __________________ select for the most desired traits.
10. Name three types of resources that individuals must compete for in nature.
11. What is another name for artificial selection?
12. Describe how you could use artificial selection to breed pigeons with large beaks.
13. Define fitness.
14. An adaptation is a heritable _________________________ that increases and organism’s ability to survive
and reproduce.
15. Explain the meaning of the phrase “survival of the fittest.”
16. What is the difference between artificial selection and natural selection?
17. Under what conditions does natural selection occur? (There are three.)
18. What may happen to a species if its environment changes faster that it can adapt?
For Questions 18–20, write True if the statement is true. If the statement is false, change the underlined word or words to make the statement true.
19. Natural selection acts on acquired traits.
20. Any inherited characteristic that increases an organism’s chance of survival is considered an adaptation.
21. Natural selection is the ability of an individual to survive and reproduce in its specific environment.
22. Below is a partially completed flowchart that models how natural selection drives evolution. The missing steps are listed below, out of order, and lettered A–D. Write the letter of the missing step in a blank box in the flowchart.
A. Adaptations are passed on to the next generation.
B. The accumulation of adaptations may lead to the evolution of a new species.
C. These offspring have few or no offspring of their own.
D. Some offspring inherit traits that increase fitness (adaptations).
Some offspring inherit traits that decrease fitness.
Individuals in a population have many variations.
Over time, adaptations accumulate in a population.
23. Natural selection depends on the ability of organisms to , which means to leave descendants.
24. Every organism alive today from ancestors who survived and reproduced.
25. Over many generations, adaptation could cause successful species to into new species.
26. Common descent suggests that all species, living and extinct, are .
27. The principle that living species descend, with changes, from other species over time is referred to as _____________________________________________.
28. The provides physical evidence of descent with modification over long periods of time.
Suppose that the water in a pond gets darker over a period of four years. The diagrams and table below show what might happen to a frog population living in the pond.
29. Use the diagrams below to complete the table.
Adaptations of Frog Populations Over Time
Year Light-Colored Frogs Dark-Colored Frogs
1 6
2
3
4
Use the diagram and table to answer questions 30-32.
30. In which year was the number of light-colored frogs greater than the number of dark-colored frogs? _____
31. How did the numbers of light- and dark-colored frogs change over time?
32. Which adaptation is best suited to life in the pond in Year 3? Circle the answer.
light coloring dark coloring
33. What causes differences between individuals? What types of changes are likely to stay in the population?
Year 1 Year 2 Year 3 Year 4
16.4
Lesson Objectives
Explain how geologic distribution of species relates to their evolutionary history.
Explain how fossils and the fossil record document the descent of modern species from ancient ancestors.
Describe what homologous structures and embryology suggest about the process of evolutionary change.
Explain how molecular evidence and genetics can be used to trace the process of evolution.
Lesson Summary
Biogeography Biogeography is the study of where organisms live now and where they and their ancestors lived in the past. Two biogeographical patterns are significant to Darwin’s theory:
The first is a pattern in which closely related species differentiate in slightly different climates. The Galápagos tortoises and finches follow this pattern.
The second is a pattern in which very distantly related species develop similarities in similar environments. The rheas, ostriches, and emus fall into this pattern.
The Age of Earth and Fossils
Radioactive dating techniques have confirmed that Earth is ancient—approximately 4.5 billion years old.
Recent fossil finds document intermediate stages in the evolution of many groups including whales, birds, and mammals.
Comparing Anatomy and Embryology
Homologous structures are shared by related species and have been inherited from a common ancestor.
Similarities and differences among homologous structures help determine how recently two groups shared a common ancestor.
• Body parts that share a common function, but neither structure nor common ancestry, are called analogous structures. Analogous structures do not provide any evidence for evolutionary descent.
• Homologous structures that are greatly reduced in size or have little to no function are called vestigial structures.
• Many homologous structures develop in the same order and in similar patterns during the embryonic, or pre-birth, stages of related groups. These similarities provide further evidence that the animals share common ancestors.
Genetics and Molecular Biology At the molecular level, the universal genetic code and homologous molecules such as genes and proteins provide evidence of common descent. In general, the fewer differences between the genes of species, the more closely-related they are.
34. Biogeographers study where organisms live now and where they and their lived in the past.
35. When individuals from a mainland bird population immigrate (move) to various islands, natural selection
may result in , but different, island species.
36. Distantly related organisms may be similar if they live in .
37. Use the words in the box and what you know about the evidence supporting evolution to complete the chart.
Type of Evidence What It Reveals
homologous structures Different species have similar structures which have been inherited from a common ancestor.
Animals with backbones have a common ancestor, as shown by how these organisms develop before they are born.
Intermediate forms show that organisms have changed over time.
Species have adapted over time to local conditions.
Almost all organisms share a common genetic code.
38. Complete the table about types of anatomical structures.
Types of Anatomical Structures
Structure Type Description Example
Structures that are shared by related species and that have been inherited from a common ancestor
Body parts that share common function, but not structure
Body parts in animals that are so reduced in size that they are just vestiges, or traces, of homologous structures in other species
For Questions 38–42, match the structure with the correct type. A structure type may be used more than once.
Anatomical Structure
39. bat wing and mouse arm 40. reptile foot and bird foot 41. dolphin fin and fish tail 42. eyes on a blind cave fish 43. snake tongue and dog nose
Structure Type A. homologous structure B. analogous structure C. vestigial structure
biogeography genetics
fossil record embryological development
44. What is the difference between a homologous structure and an analogous structure?
Use the illustrated homologous structures to answer Questions 45–17.
45. How are the forelimbs similar?
46. How are the forelimbs different?
47. How are homologous structures such as forelimbs evidence for common descent?
48. What is a vestigial structure? Give an example of a vestigial structure.
49. How does the pattern of embryological development provide further evidence that organisms have descended from a common ancestor?
50. The science of provides molecular evidence that supports evolutionary theory.
51. All living cells use and to code heritable information.
52. Based on the DNA sequences below, which two animals are most closely-related?
Which two are most distantly related?
53. The picture below shows how finch beaks are similar to certain kinds of hand tools. Suppose a finch fed on insects that burrowed into small holes on tree trunks. What type of tool do you think this finch’s beak would resemble? Explain your answer.
