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Chapter 22: Descent With
Modification
A Darwinian View of Life
On the Origin of Species by Means of
Natural Selection by Charles Darwin
 Attempts to create a family tree for all
life on Earth
Mechanism=
natural selection
Groundwork for Darwin’s Theory

Taxonomy


Paleontology



Cuvier
Study of fossils
Gradualism


Linnaeus- group organisms based on similar
structures
Change is slow but continuous
Lamarck’s Theory

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
First to include gradualism
Use & disuse
Inheritance of acquired characteristics
Natural Selection


Population CAN change over generations if
individuals with better adaptations leave more
offspring
Evolutionary adaptation


Inherited characteristics that enable survival and
reproduction in a certain environment
Evolution


Change in genetic composition of a population over
time
Descent with modification (Darwin’s term)


All organisms are related through descent with an ancestral
organism
Modifications in species a result of inhabiting different
environments
Natural selection

Requirements
Resources are limited



Struggle for existence
Individuals with heritable traits better suited
to environment leave more offspring
Population gradually evolves to exhibit higher
number of individuals with beneficial trait
Natural Selection


INDIVIDUALS DO NOT EVOLVEPOPULATIONS CAN!!!!
Environment determines which traits are
favored

Biogeography- similarities found among
species in similar ecological niches
Convergence- unrelated species in similar niches
have similar adaptations
 Divergence- related species in different ecological
niches have dissimilar adaptations


Environment does not create change- it
selects for individuals who already
possess beneficial adaptation
Examples of natural selection at
work



Guppy sexual maturation age & predatory
pressure
Drug resistant HIV
Insecticide resistance in insects
Evidence


Fossil record
Homology





related species have similar underlying traits
that MAY be used for different functions
Homologous structures
Comparative embryology
Vestigial structures (remnant structures)
Molecular similarities (DNA, protein)