1. Interest Grabber One Big Family?
Section 18-2
One Big Family?
How can you determine if one organism is closely related to another? It may seem easy, but it isn’t, and looks are often deceiving. For example, roses and orchids are both flowering plants, but roses grow on bushes or vines and have thorns. Many orchids don’t even grow in soil—they can grow in trees! Rose and orchid blossoms look very different, and roses and orchids cannot produce hybrids, or offspring of crosses between parents with different traits.

2. 18–2 Modern Evolutionary Classification
Section Outline
Section 18-2
18–2 Modern Evolutionary Classification
A. Which Similarities Are Most Important?
Evolutionary Classification
1. Phylogeny: evolutionary relationships among organisms

3. Section Outline
Section 18-2
2. Organisms now grouped into categories that represent lines of evolutionary descent
3. This is called evolutionary classification and is based on:
* derived characteristics
* similarities of genetic material
* molecular clocks

4. Classification Using Cladograms
Section Outline
Section 18-2
Classification Using Cladograms
1. Shows evolutionary relationship of organisms based on derived characteristics

5. CLASSIFICATION BASED ON VISIBLE SIMILARITIES
Traditional Classification Versus Cladogram
Section 18-2
Appendages
Conical Shells
Crustaceans
Gastropod
Crab
Barnacle
Limpet
Crab
Barnacle
Limpet
Molted exoskeleton
Segmentation
Tiny free-swimming larva
CLASSIFICATION BASED ON VISIBLE SIMILARITIES
CLADOGRAM

6. CLASSIFICATION BASED ON VISIBLE SIMILARITIES
Traditional Classification Versus Cladogram
Section 18-2
Appendages
Conical Shells
Crustaceans
Gastropod
Crab
Barnacle
Limpet
Crab
Barnacle
Limpet
Molted exoskeleton
Segmentation
Tiny free-swimming larva
CLASSIFICATION BASED ON VISIBLE SIMILARITIES
CLADOGRAM

7. Figure 18-13 Cladogram of Six Kingdoms and Three Domains
Section 18-3
DOMAIN ARCHAEA
DOMAIN EUKARYA
Kingdoms
Eubacteria
Archaebacteria
Protista
Plantae
Fungi
Animalia
DOMAIN BACTERIA

8. Similarities in DNA and RNA
Section Outline
Section 18-2
Similarities in DNA and RNA
More similar the DNA, more closely related (share a more recent common ancestor)

9. Click a hyperlink to choose a video. Panthera leo?, Part 1
Videos
Click a hyperlink to choose a video.
Panthera leo?, Part 1
Panthera leo?, Part 2
Video Contents

10. Click the image to play the video segment.
Panthera leo?, Part 1
Click the image to play the video segment.
Video 1

11. Click the image to play the video segment.
Panthera leo?, Part 2
Click the image to play the video segment.
Video 2

12. Go Online Links from the authors on the search for new species
Interactive test
For links on classification, go to and enter the Web Code as follows: cbn-5181.
For links on domains of life, go to and enter the Web Code as follows: cbn-5183.
Internet

13. Interest Grabber Answers
1. Consider the task facing early biologists who attempted to organize living things. How might they have begun?
Students may say that early biologists attempted to formulate logical systems for organizing the diversity of life.
2. Suppose that you have been given a green plant, stringy brown seaweed, a rabbit, a mushroom, a worm, and a grasshopper. You’ve been asked to organize these things into categories that make sense. How would you do it?
Students may group the plantlike, sessile organisms (the plant, seaweed, and mushroom) together, grouping the others as animals.
3. Decide on your categories and write each on a sheet of paper. Next to each category, write the defining characteristics of that category. Then, write in the organisms that fall into each category.
Remind students that organizational systems are human-made, and there are no right or wrong ones. Some, however, are more useful than others.
Section 1 Answers

14. Interest Grabber Answers
1. Do you think roses and orchids are closely related? Explain your answer.
Students may say that their different growth habits and inability to hybridize indicate that they are not closely related.
2. Now, apply the same logic to dogs. Different breeds of dogs—such as a Labrador retriever and a collie—can breed and produce offspring. So what is the difference between the rose-orchid combination and the Lab-collie combination?
Students may know that all domestic dogs are a single species.
3. What defines a species? Is appearance important? What other factors might be considered?
Students may suggest that a species is defined by its members’ ability to interbreed, regardless of appearance.
Section 2 Answers

15. Interest Grabber Answers
1. What categories could you use to organize your count of vehicles?
Students’ answers may include, type of vehicle, color, age, or manufacturer.
2. Look at your list of categories. Are all of them equally useful?
Students may suggest that the usefulness of the criteria depends on the intent of the study.
3. Is there more than one valid and useful way to organize living things?
Students should conclude that the same set of living things could be categorized in several ways, depending upon the criteria used.
Section 3 Answers

16. This slide is intentionally blank.
End of Custom Shows