Vestigial Structures A vestigial structure is a structure or organ that through the course of evolution has either diminished in size or usefulness. It is believed that the human appendix, wisdom teeth and tail bone are vestigial structures, because they are diminished in size or usefulness from what they would have been much earlier on in the course of our evolution. Analyze the pictures above. Suggest a possible function for each structure and explain why it became vestigial (why that adaptation became less important for survival). Think about organisms that are closely related to us and the functions they have for those structures (meaning other mammals or specifically other primates). Record your answers in the table Structure Possible Function(s) Why it is considered vestigial Appendix Muscles that make hair stand up Coccyx (tail bone) Muscles that move ears Wisdom teeth Gradual changes have occurred through time that have in some cases reduced or removed the function of some body structures and organs. The penguin s wings and the leg bones of snakes are examples of this phenomenon. 1) The cave fish and minnow shown below are related, but the cave fish is blind. a. Explain why eyesight is not an important adaptation to life in a cave. b. Does the appearance of the cave fish and minnow suggest common ancestry? Why?
Embryology Many scientists use what an organism looks like as an embryo, or embryology, as evidence for evolution. The embryos of most vertebrates look very similar and have similar structures. For example, fish, bird, rabbit, and human embryos are similar in appearance in early stages. They all have gill slits and a tail with muscles to move it. Later as the embryos develop, they become less and less similar. Embryology Using complete sentences, describe how comparing early development can help scientists learn about the relatedness of species.
Homologous and Analogous Structures These structures are formed in similar ways during embryonic development and share similar arrangements; however, they have somewhat different forms and functions. They are called homologous structures. Homologous Structures Carefully examine the drawings of the bones shown below. Look for similarities among the various animals. a) Describe the function of each set of bones below. Animal Human Whale Cat Bat Bird Crocodile Function b) Are the bones arranged in a similar way in each animal?
Analogous Structures Some apparently unrelated animals have organs with similar functions, yet are very different in structure and form. These structures are called analogous structures. 1) Examine the butterfly wing and the bird wing shown below. a) What function do these structures share? b) How do these structures differ? c) Do you think the bird s wing and the insect s wing came from a common ancestor? Why or why not? Some apparently unrelated animals have organs with similar functions, yet are very different in structure and form. These structures are called analogous structures.
Fossils Fossil Evidence Darwin discovered many fossils during his journeys aboard the HMS Beagle and compared them to living organisms in the surrounding areas. The organisms above are from South America, one of the continents he visited. 1. What are the similarities and differences between the glyptodont (glip tuh dahnt) fossil and the armadillo? 2. What inference can you make about their existence? Fossils Study the figure at below. Which rock layer is the oldest? Which rock layer is the youngest? Explain what can scientists learn about evolution when comparing different fossils in different rock layers? (Use terms like relatedness, extinction, transition etc.) You must write at least two complete sentences.