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Wednesday, February 3, 2016 • HOMEWORK: None • OBJECTIVE: I will be able to understand evolution is learning to recognize variation within species by examining different variations. • DO NOW: – Define evolution in your own words. – What do you think a variation in a species is? Scientists estimate there are over 8.7 million species alive on earth. This may be less than 1% of all the species that have ever existed on earth! How did so many species come about? How did these species evolve? A subset of the species Mexican Tetra (Astyanax mexicanus) lives in dark caves and many, many generations ago the fish in the population had eyes and silver color, but now they don’t. Why did this happen? Other kinds of animals have also lost their sight in caves over many generations. Kentucky Cave Shrimp Texas Cave Salamander Blind Cave Catfish Cave Crawfish Male Video Female The male red back spider sacrifices himself by throwing himself into the females fangs as he mates with her. Why do you think this happens? Male Female Male peacocks have long colorful tail feathers and females do not. Why do you think they have long colorful feathers? Why do males have them, but females don’t? Many bacteria are becoming resistant to antibiotics. MRSA is a kind of bacteria that infects people. Years ago, MRSA could be killed by many kinds of antibiotics. Now MRSA is resistant to many of these antibiotics. How did this occur? The rough skinned newt produces a toxin that is unusually strong. It is the most poisonous animal in the United States. One newt has enough poison to kill over a dozen people. Why does the newt produce so much toxin? The average horn size of bighorn sheep today is smaller than it was 30 years ago. Why are their horns smaller? The average head size of a red-bellied black snake born in the last few years is smaller than the average head size of those born 50 years ago. The average body size stayed the same. Why has the average head size changed since 50 years ago? Male guppies from one stream are very colorful while in other streams they are less colorful. More Colorful Less Colorful In a severe drought, some finches survived and others didn’t. Why? Why has the flower population changed? But the pesticides are no longer working as well! Why are more bed bugs surviving after pesticides are used? Why are most moths in those woods lighter today? Closure Based on what you learned so far, what do you think a variation is? Closure 35 million years ago, a large mammal called moeritherium lived on the earth. Moeritheriums are the ancestors of elephants. Moeritheriums had small ears and a short snout (or nose). Modern African elephants have big ears and a long trunk. Write an explanation about either the ears or the trunk. (You don’t need to write about both.) Closure Explain why the ears or trunk of a modern day elephant are different from the ears or snouts of moeritheriums. How did the change occur? Also, moeritheriems do not have tusks but modern African elephants do have tusks. Why do you think this change occurred?