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The Theory of Natural Selection

The Theory of Natural Selection. Artificial Selection. Defined : Humans select (not naturally) traits thought to be advantageous Humans created diversity choosing specific traits to breed Dogs, Crops, Livestock Only heritable traits can be passed down

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The Theory of Natural Selection

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  1. The Theory ofNatural Selection

  2. Artificial Selection • Defined: Humans select (not naturally) traits thought to be advantageous • Humans created diversity choosing specific traits to breed • Dogs, Crops, Livestock • Only heritable traits can be passed down • Importance: Shows life can change over a period of time

  3. Dog traits have been selected by breeders for centuries to produce various breeds.

  4. Plants have been bred to produce certain traits for human use also!

  5. Natural Selection With adaptation Without adaptation Not all these wildebeest will survive These kittens have variations • Four factors: • Overpopulation: more offspring are born than can survive 2) Variation: individuals of a population have differences 3) Adaptation: Some variations allow a better chance of survival 4) Descent w/ modification: Over time, those with advantages make up most of the population.

  6. The Myth The Truth Natural selection can act only on traits that already exist

  7. Which rabbit is best adapted to this environment? Over time, those not adapted most likely die…that’s natural selection!

  8. Which rabbit is best adapted? Do the dark rabbits turn white? No! They get eaten. (survival of the fittest)

  9. Struggle for Survival • Fitness: measure of the ability to survive & produce more offspring • As environments change… • Those with adaptation: more likely to survive & reproduce • Those without adaptation: more likely to perish • Populations do not grow unchecked • Limiting Factors: food, water, shelter, disease, predators

  10. Sexual Selection • Defined: a trait that increases mating success. • Ex: Bright coloring or large antlers • There are two types: • Intrasexual selection: competition among males • Intersexual selection: males display certain traits to females • Mating can have an important effect on the evolution of a population • Occurs due to higher cost of reproduction for females. • Males produce many sperm continuously • Females are limited in the number of offspring they can produce

  11. Review • What is artificial selection? • What is natural selection? • How does natural selection lead to population changes? • Why don’t populations (such as deer) continue to grow unchecked? • Compare the two different types of sexual selection.

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