Natural Selection

Your Definition How would you describe the mechanism of natural selection?

Natural Selection... is the primary mechanism of evolutionary change changes the genetic make-up of a population is the “survival of the fittest”

Why is “reproduction of the fittest” a better description than “survival of the fittest?” –Fitness = leave the most descendants

Necessary conditions for natural selection 1.Genetic variation in a population 2.More offspring produced than can be supported by environment 3.Organisms compete and resources limited 4.Differential reproduction - individuals most suited to environment reproduce –“reproduction of the fittest” 5.Over time, beneficial gene becomes more common and population changes

Acquired Characteristics vs. Natural Selection Variations are purposeful Variations are the result of an organism striving to be better Variations are random Variations due to genetic mutation

Natural Selection Examples

Using the variation in snail shells (as seen in the picture), make up a scenario in which natural selection might occur in this snail population.

Biogeography plorations/tours/stories/middle/G8.htmlhttp:// plorations/tours/stories/middle/G8.html

Biogeography Write down one observation you can make about how the yellow line moves. What is the explanation (inference) for why the same type of tree is found in many parts of the world?

Common Ancestor Geographic Isolation

A Variety of Beaks Reproductive Isolation

Divergent Evolution

Explain the following statement... Speciation occurs through divergent evolution.

Extinction Extinction is the ultimate fate of all species 99.9% of all the species that have ever existed are now extinct

Factors affecting speciation and extinction large-scale movement of the continents gradual climate changes rapid climate changes

Speciation - Extinction = Biodiversity

Variations in Guppies

Selecting a Variety of Peppered Moths