Evidence of Evolution Activity
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| Blind cave fish, Astyanax fasciatus mexicanus,
live in freshwater pools like this one within the dark caverns of three caves in San Luis Potosi, Mexico In one of the world's more recent - and evident - examples of evolution, fish from the species Astyanax fasciatus (a type of tetra) migrated into a system of dark caves in Mexico and lost all need for their eyes, so the useless organs gradually disappeared. Now a separate subspecies named Astyanax fasciatus mexicanus, these fish are born with functional eyes, but after about two weeks, the eyes become distorted and partially enclosed in tissue. As the young fish grow, their rudimentary eyes shrink and become completely covered, leaving them eyeless and blind. Although they have lost their sight, blind cave fish have gained other senses that help them to live in the dark. An especially keen sense of smell guides them toward their favorite food sources, including animal or plant remains that wash into the caves and nutrient-rich bat droppings that fall from the craggy ceilings. Another sense, which is still being studied by researchers, prevents the fish from bumping into both each other and their surroundings. Although a number of physiological changes have taken place since these fish moved into their blackened home, they split off from their seeing relatives recently enough that the two subspecies can still interbreed. Directions: Answer us based on your new understanding. a. Explain why eyesight is not an important adaptation for life in a cave. b. Does the appearance of the cave fish and minnow suggest common ancestry? Why? III. Human vestigial structures. Organs or structures that have lost their function in the organism and become reduced in size (because of efficiency) are called vestigial structures. Human vestigial organs are well documented. Directions: Read the list of human vestigial structures shown in the table below. Suggest a possible function for each structure and explain why it became vestigial. Record your answers in the table.
IV. The appendix is a small outgrowth at the lower part of the large intestine. In some plant eating animals, it is much larger - and is important in digestion. Sometimes, a person's appendix become infected and is removed. Surgeons have removed millions of appendixes. No bad side-effects have been noted after its removal. Directions: Answer based on your new understanding. a. What does this prove? Download 3.1 Mb. Share with your friends:
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