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Transcript
Theory of Evolution
& Natural Selection
Theory
• In science, theories are statements or models that
are used to support facts.
• Theories have some important properties:
– They explain a wide variety of data and observations
– They can be used to make predictions
– They are not absolute, they serve as a model of
understanding the world and can be changed as the world
view changes
The theory of evolution remains one of the
most useful theories in biology because it
explains many questions and observations.
Some questions that can be answered by
evolution.
• Why do so many different animals have the same structures, the arm
bones in a human are the same bones as a flipper in a whale?
• Why do organisms have structures they no longer use, like the appendix in
a human? Non functioning wings in penguins
• Why are there bones and fossil evidence of creatures that no longer exist?
What happened to these creatures?
• Why do so many organisms' morphology and anatomy follow the same
plan?
• Why is the sequence of DNA very similar in some groups of organisms but
not in others?
• Why do the embryos of animals look very similar at an early stage?
Evolution
• Evolution = change over time
Evolution of Species
• The change in a population of organisms over
time caused by both genetic change and
environmental factors.
History of Evolutionary
Thought
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Early Ideas On Earth’s Organisms
• Aristotle believed
species were fixed
creations arranged
by their complexity
• Idea lasted 2000
years
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Early Ideas On Earth’s Organisms
• Linnaeus – 1st to group
similar organisms and
assign them Latin
names
• Two word name
(Genus species)
• Known as Binomial
nomenclature
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Lamarck
• Jean-Baptiste Pierre Antoine de Monet,
Chevalier de la Marck (1744 - 1829), often just
known as "Lamarck.”
• Naturalist who lived before and during
Darwin’s lifetime
Lamarck
• Ideas that were proven to be untrue
– Traits evolved through use or disuse (Ex. neck of
giraffe, wings of a penguin)
– Traits acquired over an individual's lifetime could
be passed down to its offspring (Ex. Bodybuilder)
• Ideas that Darwin built upon
– Evolutionary change takes place gradually and
constantly
Lamarck’s Theory of Evolution
• Jean-Baptiste Lamarck, 1809
• One Of First Scientists To
Understand That Change
Occurs Over Time
• Stated that Changes Are
Adaptations To Environment
acquired in an organism’s
lifetime and passed to
offspring
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12
Lamarck’s Theory of Evolution
• Idea called Law of
Use and Disuse
• If a body part were
used, it got
stronger
• If body part NOT
used, it
deteriorated
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14
Lamarck’s Mistakes
• Lamarck Did NOT Know how traits were
inherited (Traits are passed through
genes)
• Genes Are NOT Changed By Activities In
Life
• Change Through Mutation Occurs
Before An Organism Is Born
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15
Lamarck’s Theory of Evolution
• Inheritance Of Acquired Traits
– Traits Acquired During Ones Lifetime Would Be
Passed To Offspring
Clipped ears of dogs could be passed to offspring!
16
Charles Darwin the
Naturalist
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Charles Darwin
•
•
•
•
1809 – 1882
Born in England
Biologist & Naturalist
Explored Galapagos Islands
on the HMS Beagle
• Wrote On the Origin of
Species
Darwin’s Voyage of Discovery
A reconstruction of the HMS Beagle sailing off Patagonia.
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19
Darwin Left England in 1831
Darwin returned
years later in 1836
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cmassengale
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HMS Beagle’s Voyage
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The Galapagos Islands
• Small Group of Islands 1000 km West of
South America
• Very Different Climates
• Animals On Islands Unique
• Tortoises
• Iguanas
• Finches
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Galapagos Islands
• Vast number of
endemic species,
found only on the
islands
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Darwin’s Observations &
Conclusions
The Struggle for Existence
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Voyage of the Beagle
During His Travels, Darwin Made
Numerous Observations And
Collected Evidence That Led Him To
Propose A Revolutionary Theory
About The Way Life Changes Over
Time
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Darwin’s Observations
• Patterns of Diversity
were shown
• Unique Adaptations in
organisms
• Species Not Evenly
Distributed
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Adaptation
• Process where a population becomes better suited to
its environment This process takes place over many
generations.
• May also refer to a feature which is especially
important for an organism's survival.
Definition
• Evolution is the
slow , gradual
change in a
population of
organisms over
time
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Darwin’s Conclusion
• If there are more individuals
than can be supported by the
environment there will be a
struggle for existence among
individuals
• Only a fraction of the offspring
survive each generation
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Darwin’s Observations
• Individuals of a population
vary in their
characteristics with no
two individuals being
exactly alike.
• Much of this variation
between individuals is
genetically inheritable.
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Darwin’s Conclusion
• Individuals who inherit
characteristics most fit
for their environment
are likely to leave more
offspring than less fit
individuals
• Called Natural Selection
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Natural Selection
• Survival of the Fittest
• Fitness = ability to survive
• Darwin’s theory that life forms better adapted
to their current environment have a better
chance of surviving and will pass on their
traits to their offspring
• Natural selection -> Evolution
Darwin Presents His Ideas to the
public
On the Origin of Species
published in 1859
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Publication of “On The Origin of
Species”
• Upon His Return To England, Darwin
Developed His Observations Into The Theory
of Evolution
• But He Did Not Publish For Almost 25
Years –
Why?
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Publication of “On The Origin of
Species”
• Darwin Knew That His Theory Would Be
Extremely Controversial And Would Be
Attacked
• His Theory Challenged Popular Beliefs
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Publication of “On The Origin of
Species”
• Darwin read an Essay From Alfred
Wallace
– Fellow Naturalist
– Independently Developed The
Same Theory that species changed over
time because of their struggle for
existence
• When Darwin read Wallace’s essay, he
knew he had to publish his findings
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5 Major of Points of Darwin’s Theory
of Evolution by Natural Selection
1. Populations have Variations
2. Some Variations are favorable
What type of finch would be most fit to live in an
area with many seeds available to eat?
3. More offspring are produced than
survive
If more offspring die than are
produced this eventually will result in
extinction, when a species no longer
exists
4. Those that survive have favorable
traits (the most fit)
Peppered Moths
5. Populations will change over time
Common Descent with
Modification
• Darwin proposed that
organisms descended
from common
ancestors
• Idea that organisms
change with time,
diverging from a
common form
• Caused evolution of
new species
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Theory of Evolution
Supporting
Evidence
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Evidence of Evolution
Darwin Argued That Living Things Have Been
Evolving On Earth For Millions of Years.
Evidence For This Process Could Be Found
In:
– The Fossil Record
– The Geographical Distribution of Living
Species
– Homologous Structures of Living Organisms
– Similarities In Early Development
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Evidence to Support Evolution &
Natural Selection
• Comparative Anatomy
• Geology & Fossils
• DNA research
Comparative Anatomy
• Study of similarities and differences in the
anatomy (structure) of different organisms.
• Indicates that various organisms share a
common ancestor.
Homologous Structures
• Features of organisms that may not perform
the same function but share similar anatomy.
Homologous Structures
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Embryology
• The study of developing organisms
• Embryo – early stages of vertebrate
development
Similarities In Early
Development
• Embryonic Structures Of Different Species
Show Significant Similarities
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Ex. Similarities of chordates
• 1. Pharyngeal slits
• 2. Notochord
3. Dorsal, hollow nerve cord
4. Posterior elongation of body
Evidence for Evolution - Comparative Embryology
Similarities In Embryonic
Development
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Geological & Fossil Evidence
• By comparing layers of rock from different
parts of the world, the sequence from the
very earliest life to the present can be
observed in fossils, in this way the fossil record
shows a change from simple to complex
organisms.
DNA evidence
• DNA in every organism shares the same amino
acid base pairs
– (A/T, C/G)
• Different amount of pairs
• Different sequence of pairs
Phylogenic Tree
• Life forms have evolved
from simple organisms
in oceans through
amphibians to higher
forms such as primates.
Common Descent with
Modification
• Darwin proposed that
organisms descended
from common
ancestors
• Idea that organisms
change with time,
diverging from a
common form
• Caused evolution of
new species
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Common Ancestor
• An organism or group of organisms to which
two or more species can trace their history
Phylogenic Tree
• Life forms have evolved
from simple organisms
in oceans through
amphibians to higher
forms such as primates.
Modern Evolutionary Concepts
Gene Pool
• All of the alleles
(genes) in a
population of
species
• Also called allele
frequency
Genetic Drift
• Change in the frequency of alleles in a
population’s gene pool through mutation,
reproductive isolation, or chance
Mutation
• A change in DNA, usually results from a
mistake during mitosis
• Can be helpful, harmful or have no effect on
an organism
Reproductive Isolation
• What is Isolation?
• Reproductive Isolation = Processes or
behaviors that prevent a species from
reproducing
– 3 Types
Temporal Isolation
• When timing does not
allow for reproduction
• Ex. Winter vs. Summer
Rabbits
Behavioral Isolation
• Different mating rituals
Geographic Isolation
• Organisms are
separated by land or
water features
Speciation
• New species can develop when part of the
population becomes separated and evolves in
isolation.
Founder Effect
• Loss of genetic variation that occurs when a
new population is established by a very small
number of individuals from a larger
population.
Bottleneck Effect
• Reduction in size and genetic variation in size
of a population due to natural disasters,
disease or predators.
Biodiversity
• Evolution & Natural Selection can lead to
biodiversity
• Biodiversity = Variety of species living in the
same habitat or environment
Benefits of Biodiversity
•
•
•
•
Reduces competition
Helps to cycle nutrients and waste
Medicine & Food
Industry & Leisure