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Baylor University - ENV 1301 - Class Notes - Week 3

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Baylor University - ENV 1301 - Class Notes - Week 3

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background image Environmental Science- Class Notes (09/12- 09/14)  Natural Selection:  Common descent- The idea that all life on earth is related through a common ancestor.  Descent with modification- Parents pass traits to their children, but children are different from 
their parents and from their siblings.  
Natural Selection gave credibility to the theory of evolution because it provided a natural 
mechanism for it.  
It is based on the idea that creatures with certain beneficial traits will survive and pass those 
traits on to their offspring while those who do not have the beneficial traits will die off.  
Evidence that led to idea of Natural Selection:  Throughout history, people have domesticated animals by breeding them to have the traits that 
benefit us.   
Galapagos tortoises- Tortoises on different islands were similar, but were different enough to be 
considered separate species.  The differences between the species corresponded with what was 
beneficial to life on the specific island that each species lived on.  
Evidence for Evolution:  Comparative anatomy, embryology, fossil record, DNA comparisons  Example of cetaceans (whales and dolphins):  o  Comparative anatomy- Whales have placentas and give live birth like other mammals.   They also have blowholes which are like mammal noses and a strange pair of bones 
where leg bones should be. 
o  Embryology- The embryos of dolphins and humans look similar (as do those of many  other animals).  o  Fossil record- Fossils of whales from long ago had the blowhole closer to the front of  their face like a nostril. Other fossils seem to reveal a whale-like species with legs.  o  DNA comparisons- Whale DNA is very similar to the DNA of hippos.  They also have  similar features which seem to indicate a common ancestor.   o  All of these things point to whales descending from a four-legged ancestor.  There are many similarities between bird wings and reptile claws.   There seems to be evidence that mammals descended from reptiles which descended from 
amphibians which descended from fish.  
How Evolution Works:  Creatures are of the same species if they can reproduce with each other offspring which can 
also reproduce.  
More offspring are produced than are needed, which creates more diversity within a species.   Recombination- DNA of two parents is combined  Mutation- DNA changes slightly, making offspring different from parents  The offspring with more beneficial traits survive and pass on their traits while those with less 
beneficial traits die. 

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School: Baylor University
Department: Environmental Science
Course: Exploring Environmental Issues
Professor: Larry Lehr
Term: Spring 2016
Tags: evolution
Name: ENV notes 3
Description: Evolution, Natural Selection and Food Webs
Uploaded: 09/19/2016
2 Pages 22 Views 17 Unlocks
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