Darwin s Postulates Continued Variation is heritable Postulate 2 Some of an individual s variation is passed on to its offspring Postulate 3 In every generation more offspring are produced than can survive Struggle for existence survival Example Mola Mola Lays 3 million eggs Example 2 Beetles Boris and Natasha They mate and produce 10 offspring Environment only allows for 5 of the offspring to live Postulate 4 Offspring that survive AND reproduce may have inherited variation that gives them an advantage Imagine that the 5 survivors from the last example had longer legs than their siblings o Longer legs increased speed to avoid predators and get food faster o Variation allowed for increased survival and growth This increases the likelihood of reproduction Increases their fitness NOT equal to quickness or physical agility It is an index of reproductive success Fitness increases with increased reproductive outputs Important that they survive AND reproduce Fitness 0 if no offspring are produced Survival of the fittest Now imagine that the same struggle to survive and reproduce is repeated over 1000 s of generations o Each successive generation of beetles will be slightly quicker longer legged May change so much that speciation occurs Evolution by Natural Selection One mechanism by which evolution occurs Requires that variation is adaptive and results in selection for or against organisms survival and reproduction 1 Variation must exist for given trait a Without variation selection does not affect survival in any way b All individuals respond the same to a given selective pressure c There are no advantages to be passed on to future generations 2 Variation leads to differential survival fitness a Peppered moth industrial melanism Percent of moth population 80 70 60 50 40 30 20 10 Light morph moth Dark morph moth 0 1850 Industrial Revolution Change in Industry Practice b Food availabilities can change Natural Selection i Example Ground Finch has variability in its beak bill characteristics Shorter thicker beaks allow the finch to eat larger seeds Narrow thin beaks allow for the finch to eat smaller seeds 3 Variation must be heritable a Can be passed on to offspring Lamarck 1744 1829 Evolution by acquired inheritance variation o Trait variation passed to offspring was based on use disuse by parents Example Giraffes have long necks because their ancestors had to stretch to reach the leaves in tall trees
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