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Change Over Time
Evolution
 Theory proposed by
Charles Darwin
 Latin word meaning
unfolding or opening out
 All living things on Earth
are changed forms of
living things that came
before
Another Definition
 Evolution can be defined as a change in
species over time.
 Species: a group of organisms that share
similar characteristics and can interbreed to
produce fertile offspring
Mutations
 Agents of change
 A change in a gene will
produce a change in the
offspring
 One major driving force
behind evolution
 Most mutations are
negative, but sometimes
they improve the
organism
Adaptation
 A change that
increases an organism’s
chances of survival is
called an adaptation
 Organisms that are
better adapted live
longer and reproduce
New species may evolve over long periods
of time
 Many small adaptations
may occur over
time…..new species
evolves
 New species may not
resemble old
 New species may result
in the extinction of
another
Populations Evolve
……not individuals
Natural Selection
 Process that results in adaptation of an organism to its
environment by means of selectively reproducing
changes in its genotype.
 This is the driving force behind evolution.
Natural Selection
 Variations that increase chances of survival and
reproduction are preserved and multiplied over
generations
 Less advantageous variations are overpowered by the
better variations.
Natural Selection
 May arise from differences in survival, fertility, rate of
development, mating success, or any other aspect of
the life cycle.
 mutation, gene flow, and genetic drift, all of which are
random processes, also alter gene abundance.
Natural Selection
 Ultimately over many generations the number of
organisms in a population with beneficial mutations
(adaptations) increases and the harmful mutations are
eliminated because those organisms that carry them
die off.
 Also known as “Survival of the Fittest”
Citation (MLA)
. Britannica Concise Encyclopedia.
Learn360. 11 March 2010
http://www.learn360.com/ShowArticle.aspx?ID=291902
Evidence to Support Evolution
 Fossil Record
 Example: Whale-like
skull found in 1983 from
50 million years
ago…boney structure for
hearing could not have
worked under
water….ancestors of
modern whales must
have spent time on land
Example of Fossil Evidence……armadillo and glyptodont
Anatomical Evidence
 Similarities in physical
structure
 Example: The shape and
arrangement of bones
for a salamander, lizard,
turtle, and opossum
 This suggests evolution
from a common
ancestor
Anatomical Evidence Continued: Similar Vertebrate Limbs
Evolution of Horses (Anatomy Continued)
Evolution of Horses Graph
Embryological Evidence
 Embryos are organisms in early stages of
development
 Growth and development are controlled by
genes
 Similarities in embryos indicate sharing a
common ancestor
Embryological Evidence Continued
Chemical Evidence
 DNA molecular
structure will be
similar if two animals
are closely related
 Example: Zebra-like
animal from 100 years
ago is 95% similar in
DNA to modern day
zebra….they share
common ancestry that
dates back 3 million
years
Molecular Evidence
 Proteins made by genes
can also be analyzed.
 The closer the
similarity in protein
structure of different
organisms, the more
recently their common
ancestor existed
Human Karyotype: Molecular Evidence
History of Life Timeline
Have we really evolved?