Natural+Selection--Perfect+Organisms?

Natural selection does not create perfect organisms because of several reasons. The first reason is

evolution is limited by historical constraints. Every organism comes from ancestral forms.

Evolution does not forget the anatomy of its ancestors and make a whole new structure; it

chooses existing structures and adapts them to a new situation. An example would be how some

bird species might benefit from having wings and four legs for a speedy get away, but instead

they become reptiles that had two pairs of limbs instead of four. The second reason is adaptations

are often compromises. Each organism must be able to many different things. An example would

be a seal who walks on rocks and would have an easier time walking on those rocks if it had

legs but it wouldn't swim as well. The third reason is the chance of natural selection interaction.

Events that happen by chance can affect the history of populations. An example of this is when a

storm blows hundreds of birds or insects over an island in the ocean. The wind does not always

transport the members of the species that are best suited for the new environment and the ones

that are transported may not contain the necessary traits needed to survive. The fourth reason is

selection can edit only existing variations. Natural selection favors the fittest organisms and those

organisms may not contain the ideal traits and new alleles will not rise on demand. Due to

these reasons natural selection cannot make a perfect organism(1).

<span style="color: #0000ff; font-family: 'Arial Black',Gadget,sans-serif;">Genetic Variation is preserved in a population by mutations, selective pressures, and genetic drift.

<span style="color: #0000ff; font-family: 'Arial Black',Gadget,sans-serif;"> Genetic Variation is important because it provides the material for natural selection(3).



(1). AP Biology Book page 469-470

(2). http://www.bio.miami.edu/~cmallery/150/unity/c7.1.23.finches.jpg

(3). http://www.eoearth.org/article/Genetic_variation

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