Natural Selection

Charles Darwin On the Origin of Species Sailed with the HMS Beagle Observations made in the Galapogos Islands These observations helped him form the theory of how species change over time called natural selection

What is Natural Selection? Natural selection is governed by the principles of genetics.

Types of Adaptations Protective Coloring –Camouflage –Mimicry Physiological Adaptations –Reproductive Changes –Other changes Behavioral Adaptations

Evidence for Evolution Fossil record Anatomy –Homologous structures –Analagous structures Vestigial structures Embryology Molecular biology (DNA differences)

What is a Population? Populations evolve over many generations, individuals don’t Populations are groups of interbreeding individuals that live in the same place at the same time Individuals in a population compete for resources with each other

How Does Evolution Work? Populations produce more offspring than the environment can support The unequal ability of individuals to survive and reproduc leads to the gradual change in a population over many generations

Mechanism for change in a population of organisms Animals who have greater fitness survive in environment and live to reproduce Random changes (mutations) can lead to greater or less fitness Adaptations allow an organism to survive better in their environment

Mutations & Variety Produced by Sexual Reproduction Allow for Diversity within a Population Genetic drift (caused by chance) –Bottleneck –Founder effect Genetic equilibrium –Hardy-Weinberg law –In H-W equilibrium, does not occur

Adaptations Can arise in response to environmental pressures –Temperature –Antibiotic resistance in bacteria –Pesticide resistance –Morphological changes in peppered moths

Types of Selection Directional –Extreme form favored by natural selection Stabilizing –Middle form most successful Disruptive –Two extreme forms successful in separate environments

How are new species created? Geographic isolation Reproductive barriers Change in chromosome numbers Adaptive radiation

Types of Evolution Convergent evolution –Dolphins & fishes –Wings of bees & bats Divergent evolution –Darwin’s finches –Adaptive radiation

How fast does evolution occur? Gradualism –Darwin –Species change slowly over time Punctuated Equilibrium –Gould & Lewontin –Species can make rapid “leaps” in evolution Modern Synthesis –Parts of both are correct