Natural Selection

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

Colouring

– 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