Download Natural Selection and Speciation PP

Natural
Selection and
Speciation
Stabilizing Selection
• favors the average individual
• reduces variation in a population
Examples
• birth weight in humans
• Siberian husky- muscle mass
• “living fossils”- organisms that
have remained unchanged
for millions of years (sharks,
crocs)
Birth Weight
Directional Selection
• favors one of the extreme variations
• leads to rapid evolution of a population
Examples
PEPPERED MOTHS
PESTICIDE/ANTIBIOTIC RESISTANCE
Disruptive Selection
• favors both extreme variations
Examples
• Darwin’s finches
–small beaked birds could eat
small seeds
–large beaked birds could eat
large seeds
–medium beaked birds could
not eat either seed efficiently
STABILIZING
DIRECTIONAL
DISRUPTIVE
Divergent Evolution
• occurs when closely related
species evolve to look differently
• populations change to adapt to
different environments
• adaptive radiation- one species
evolves into several different
species
Darwin’s Finches
Hawaiian
Island
Honeycreepers
Convergent Evolution
• occurs when species of
different ancestry evolve to
look alike
–occurs b/c species occupy
similar environments
• analogous traits
Examples
• whales and fish
• birds and butterflies
• marsupial and placental
mammals
Speciation
• evolutionary formation of a
new species