Natural Selection

• Father of Evolution

• Proposed a mechanism for evolution, natural selection

• Darwin went on a 5-year trip around the world on the ship, the HMS Beagle

  • As the ship’s naturalist, he made observations of organisms in South America and the Galapagos Islands

• Wrote a book, “Origin of the Species”​

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Charles Darwin

Natural Selection

Natural Selection: Organisms that are best adapted to an environment survive and reproduce more than others.

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Darwin's Theory of Natural Selection

Darwin’s Theory of Natural Selection occurs in four steps:

• Overproduction

• Variation

• Competition

• Selection

• Each species produces more offspring that can survive

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Overproduction

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• Each individual has a unique combination of inherited traits.

  • Adaptation: an inherited trait that increases an organism’s chances of survival

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Variation

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Why is Variation Important?

• Because the environment changes.

• The more variation within a species, the more likely it will survive

  • EX: If everyone is the same, they are all vulnerable to the same environmental changes or diseases

• The more variation of types of species in an habitat, the more likely at least some will survive

  • EX: Dinosaurs replaced by mammals

Competition

• Individuals COMPETE for limited resources:

  • Food, water, space, mates

• Natural selection occurs through “Survival of the fittest”

  • Fitness: the ability to survive long enough to reproduce

• Not all individuals survive to adulthood

Subject | Subject

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Selection

• The individuals with the best traits / adaptations will survive and have the opportunity to pass on it’s traits to offspring.

  • Natural selection acts on the phenotype (physical appearance), not the genotype (genetic makeup)

  • Ex: When a predator finds its prey, it is due to the prey’s physical characteristics, like color or slow speed, not the alleles (BB, Bb)

• Individuals with traits that are not well suited to their environment either die or leave few offspring.

• Evolution occurs when good traits build up in a population over many generations and bad traits are eliminated by the death of the individuals.​