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Transcript
Mechanisms for Evolution Natural Selection • Darwin found on his journey that certain animals were better suited for their environments than other animals • Darwin found that some of these animals were better suited to survival than others Natural Selection • Darwin believed that certain animals were better suited to survival and that helped them live and have offspring • Those animals that lived and had offspring would be the ones that you see in the world • This idea was called natural selection Natural Selection • Natural selection can only happen when one organism has an increased chance to spread its genes • The probability that an organism will pass on its genes to the next generation is referred to as fitness Natural Selection • An organism that has an increase in fitness have a larger chance of passing on their genes • An organism that has a decrease in fitness has a smaller chance of passing on their genes Overproduction • There are also several other things that Darwin noticed during his travels that helped form his opinion of natural selection • One of the things he noticed was the number of offspring that were produced Overproduction • Most animals can produce more offspring than can survive to maturity • This means that some of the offspring will die when they are young • The offspring that will die are ones that will not be passing their genes on in the gene pool Overproduction • The idea that some offspring do not survive to maturity and cannot contribute their combination of genes is called overproduction • Examples of this would be wild octopus • More octopus are produced each year than can survive Genetic Variation • Darwin also noticed that within a population there are a difference in traits • The difference in traits creates a full range of traits within a species • This is easy to observe in any population Genetic Variation • The range of traits within a population helps determine how natural selection proceeds • Natural selection tends to select for certain traits and have certain other traits die out • The range in traits is called genetic variation Genetic Variation • The range in traits allows for a species to survive if some traits are not variable • If deer with large antlers are hunted and killed easier, there will be deer that have small antlers that would survive • If there were no variation among deer, none would survive Insert Graph of Height # Of People 7 6 5 4 # Of People 3 2 1 0 4' 9" 5' 5' 3" 5' 6" 5' 9" 6' 6' 3" Adaptation • Some of the variations help an organism survive in an environment • These variations tend to become more frequent in a population • The more frequent that trait is in a population, the better chance that population will survive Adaptation • A trait that makes an individual more likely to survive in an environment is called an adaptation • Something like thick fur in a cold environment is a successful adaptation • Something like thick fur in a warm environment is not a successful adaptation Adaptation • Remember an adaptation is a something that is passed down from the parents • Adaptations are not something that is spontaneous or planned by the organism Artificial Selection • What is the process that Darwin proposed is the driving force behind evolution? • Natural selection is a process that occurs in the natural world • This means that no human can interfere Artificial Selection • Sometimes humans tamper with natural selection • This can be seen most often in dogs • Humans tend to want dogs with certain desirable traits • They breed dogs together that have these traits Artificial Selection • Artificial selection is the process of humans selecting individual traits to give to the next generation • It is the only way that we could have gotten one of these from one of these Video • Watch First! • http://www.youtube.co m/watch?v=nVSJNhUhV -4 • Watch Second! • http://www.youtube.co m/watch?v=gxeD65E_A vE • http://www.youtube.co m/watch?v=0zHnhbW0 8yQ