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NYS LabNYS Lab

Beaks of FinchesBeaks of Finches

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Survival of the Fittest

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Overproduction

• Within a population, there are more offspring produced in each generation than can

possibly survive.

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Competition• Natural resources; like food, water, and space available to a

population is limited.• Because there are many

organisms with similar nutritional requirements, there must be

competition between them for the resources needed to survive.

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Survival of the Fittest• Variations among

members of a population make some of them better adapted to the environment than others.

• It is generally the best-adapted individuals that will survive.

• The environment is the agent of natural selection determining which species will survive

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Natural SelectionThe environment determines which traits are

beneficial to the survival of an organism in a particular habitat.

Selected traits “good” tend to be retained and

passed on.

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Natural Selection1. Natural selection involves the

struggle of organisms to survive and reproduce in a given environment.

2. Traits which are beneficial to the survival of an organism in a particular environment tend to be retained and passed on, and therefore, increase in frequency within a population.

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Natural Selection

3. Traits which have low survival value to an organism tend to diminish in frequency from generation to generation. Ex: ALBINISM

4. If environmental conditions change, traits that have low survival value may now have a greater survival value.

5. Therefore, traits that prove to be favorable under new environmental conditions will increase in frequency.

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Ex: Insects resistant to insecticides

1. Genetic make-up of some insects make them resistant to the effects of insecticides.

2. Before the widespread use of insecticides, this trait was of no particular survival value.

3. With the increased use of insecticides, this trait developed a very high survival value.

4. Therefore, insects with resistance to insecticides survived and reproduced much more successfully than those lacking the trait.

5. As a result, the frequency of insecticide resistance has increased greatly in insect populations.

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Ex: Rats resistant to rodenticidesNot Immune!

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Reproduction

• Individuals that survive and then reproduce transmit these variations to their

offspring.

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Speciation

• The development of a new species occurs as variations or

adaptations accumulate in a population over many

generations.• Ex: common ancestor

Chimpanzees & Humans