The Theory of Natural Selection

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Presentation transcript:

The Theory of Natural Selection

Artificial Selection Defined: Humans select (not nature) 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

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

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

Natural Selection Four factors: With adaptation Without adaptation Not all these wildebeast 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.

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

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

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

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

Video: Part 4- How does evolution really work? https://www.youtube.com/watch?v=Pf9P0lrpgLk&index=4&list=PL18D04D3530C00CE0

Sexual Selection Defined: a trait that increases mating success. Ex: Bright coloring or large antlers There are two types: Intrasexual selection: competition among the same sexes (males vs. 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

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.