Natural Selection

Today’s Objectives: SOL BIO.8b-d

TSW investigate and understand how populations change through time, including:– How variation of traits, reproductive

strategies, and environmental pressures impact on the survival of populations

– Recognizing how adaptations lead to natural selection

– How new species emerge

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