Evolution: Natural Selection Flashcards
What are the 5 postulates?
History of earth is long
Individuals are variable
Some traits are passed on from generation to generation
Survival and reproduction are not random
More offspring are produced than can survive.
What are the four types of natural selection?
Directional, Stabilizing, Disruptive, Sexual
What is directional selection?
Selection that favours either an increase or decrease in a trait variations from the population average.
What is directional selection commonly used for by humans? Give an example of this
Artificial breeding: extreme trait variations are favoured (like bigger and sweeter strawberries)
What is an example of directional selection in nature?
Longer bills on hummingbirds to reach longer flowers for nectar.
What is stabilizing selection?
Selection against traits that deviate from the population average. (when average phenotype is preferred by the environment).
What is an example of stabilizing selection in nature?
Medium sized hummingbird bills are favoured in an environment with medium length flowers.
Longer bills take too much energy to carry around.
Shorter bills can’t reach the nectar
What is disruptive selection?
Selection that favours traits that deviate from the population average.
What is an example of disruptive selection in nature?
Environment with black and white rocks:
Black and white rabbits survive (extreme trait variation)
Grey rabbits die (average trait variation)
Or hummingbirds example with long and short flowers, no medium
What is sexual selection? What are the two subcategories of sexual selection?
Selection favouring any trait that increases the mating success of an individual
Female choosing male mates based on coloration and behaviours
Male vs male competition: body size, physical traits
Why might sexual selection hinder an individual?
Coloration and eye-catching behaviours may make an individual easier prey
