To begin to understand how physical features noted in the fossil record provide clues about the evolution of species.
This lesson is for students who already have a basic understanding of evolution. Prior to high school, students learn that the fossil record tells the story of present-day animals evolving from earlier species that are similar enough to suggest that they are related, but at the same time, distinctly different. In high school, students learn about evolutionary change—how small changes happen in species over vast amounts of time.
In general, students should have many opportunities to read about fossil finds that give clues about the origins (or possible origins) of many organisms, and the background of humans may be one of the most interesting and challenging. This lesson gives an overview of just some of what scientists know so far, focusing on physical features and how these give clues about our past. Please note: this lesson is not a complete study of this topic, and is intended to complement other instruction on it.
It will be important for you to be prepared to respond to students who challenge the content of this lesson, and handle this in a way that's in accordance with your school's policies.
Start the class with a general discussion about human ancestors. Find out what students know and believe, particularly about the physical features of our ancestors, by asking these questions:
- How long ago do you think our ancestors lived? (If students have no idea, point out that the dinosaurs became extinct 65 million years ago and we know—contrary to Hollywood movies—that humans and dinosaurs did not roam earth simultaneously. This will at least narrow down the dates.)
- What do you know about our ancestors? Their physical features? (Don't guide too heavily or correct the students' thoughts at this point; they will have a chance to revisit these ideas throughout the lesson.)
Students should use their Comparing Species through the Fossil Record student esheet to go to and read the text on the Human Evolution: You Try It page. Review the term "hominid" with students. Then they should access the Human Evolution activity by clicking on that link at the bottom of the text. Students can slide the hand across the timeline that appears, as well as roll their cursors over the images in order to learn more about the various species, paying attention to particular physical features that changed over time. When they are done, they should click on the "show tree" button to see how the hominids might have been related.
Be sure that students understand the timeline, and ask them these questions (students can use their Human Origins student sheet to answer these questions):
- Look at A. ramidus, the most primitive of hominids found. Compare and contrast humans today to A. ramidus.
- Follow the "tree" over to Lucy and then to Homo habilis "handy man." What physical changes do you note between the two?
- How do you think the use of tools by "handy man" possibly changed the lives of Homo habilis?
- Do you think those tools led to what we have today?
- Now follow the "tree" up to Homo erectus and then over to Homo sapiens. What changes in traits do you notice?
- Finally, look at Homo sapiens. Generally, how do we differ from the various species that came before us? (Think about external physical traits, bone structure, language, and culture.)
- What similarities do you think there are between humans and the species that came before?
- Do you think there are more differences or similarities?
- Can you think of other species today that have evolved from earlier species, but are quite different from those earlier species?
(Answers may vary. Encourage students to explain their responses.)
Tell students that now they will learn more background information and explore more distinct physical differences between early hominids and today's species. They will begin their investigation at The National Geographic Outpost page. At this site, students should click on "Outpost" and then "Interpretation Station." A list of four articles will appear on the right side of the page. Have students read only the first and third articles, What's a Hominid? and Hominid Family Photo Album, because they most directly address the topic of physical features.
Ask these questions to help students understand how physical features provide clues about our ancestors:
- What physical feature first separated hominids from apes? (Bipedalism.)
- What are some advantages of bipedalism? (For example, faster travel allows for better view of surroundings.)
- What did the curved fingers of the very first hominids most likely represent? (They were still needed to climb trees.)
- How did the upper limbs of hominids change over time? What do these changes indicate? (Upper limbs became shorter and the fingers more straight. These changes indicate that over time, hominids became less adapted for tree climbing.)
- How did hominid tooth enamel change over time? What does that change imply in regard to behavior? (It became thicker, therefore allowing hominids to eat a wider variety of foods.)
- How did hominid canine tooth size change over time? What may this represent? (Canine tooth size became smaller, indicating fewer violent displays and interactions.)
- Describe the usefulness of looking at fossil records. (For example, it allows scientists to make inferences about animal behavior at various points in time.)
- Describe some limitations of using fossils to piece together our past. (For example, we can't be sure we'll find enough fossils to presume a direct line of human evolution; however, we can reconstruct patterns and pathways of evolution. Be sure that students understand the evolutionary timeline as a "bush" rather than a "tree.")
Now, ask students to imagine they are out in the field assisting on a fossil dig. They should create a journal that describes a discovery they made of an early hominid fossil. They can use these sites to "find" their fossil and gather information about it:
Students can use the Comparing Species through the Fossil Record student sheet to help them do this activity. Be sure students understand the outlined requirements. When students are finished, collect the journals and use them as a tool to assess student understanding of the benchmark ideas.
There are several other activities on the National Geographic Outpost website that could be used as extensions to this lesson. Click on "Human Origins," then "Tool Kit," and then "Classroom Ideas." Relevant activities for this grade level can be found by clicking on "Grades 9 Through 12." For example, there is an introductory activity that places cladograms in the context of humans and human ancestors.
Between one and two million years ago, several different groups of ape-men roamed the plains of Africa. The only clues we have as to how they lived and evolved come from fossils they left behind. Hominid Diet, a Weekly Science Update feature, tells us what some of those fossils reveal about the unusual diet of early hominids.
Becoming Human, an online documentary, is an excellent supplementary resource for this lesson.