SESSION 3

Engage

Explore

Explain

Elaborate

Part A: 

Molecular Evidence

Part B: 

Molecular Clocks

Evaluate

Resources

Facilitator Notes

SESSION 3: What Is the Evidence for Evolution?

Elaborate Part A: Molecular Evidence

		Today, we have one additional tool not available to Darwin: molecular evidence. Surprisingly, molecular differences between species do not necessarily correlate with differences in their appearance. Watch Evolution Show Two video segment "Genetic Toolkit," then read "Animal Body Plans: Homeobox Genes" (pdf) and think about these questions: •  What is the significance for evolution of the Drosophila's set of eight homeobox genes that determine the embryo's development? •  How does the discovery of a genetic toolkit that determines segmentation relate to the Cambrian explosion?
Genetic Toolkit View in: QuickTime | RealPlayer

Since the discovery of the structure of DNA, a molecular revolution has taken place. Intense investigation by molecular biologists has uncovered new genetic links between very diverse animal species, providing new evidence of common ancestry.

For a summary of key information on molecular evidence, see "New Evidence from Molecular Biology" at the National Academy of Sciences Web site.

To learn how molecular evidence can be compared with anatomical evidence to describe relationships between organisms, do the In-depth Investigation: Molecular Connections activity from Unit 3 of the Evolution Teacher's Guide. Unit 3 pdf file | Resources for this activity

		Another activity on molecular phylogenies that you can do with your students can be found at the the National Health Museum's Access Excellence Web site.

Next: Elaborate Part B: Molecular Clocks