Transcript Darwin`s Theory of Evolution

Darwin’s Theory of Evolution
Chapter 10
The Puzzle of Life’s Diversity
Charles Darwin –
THEORY OF EVOLUTION
BY MEANS OF
NATURAL SELECTION
Made observations and
devised a theory on
how life changes over
time
Galapagos Islands and Beyond
Voyage of the HMS Beagle
Darwin was influenced by several other scientists:
-James Hutton and Charles Lyell – Studied
rock formations and changes in the earth
-Alfred Wegner - began theory of
continental drift; coined term “Pangaea”
-Jean Baptiste de Lamarck – Theory of
Inheritance of Acquired Characteristics
Darwin’s Observations
a) Patterns of
Diversity were
shown
b) Unique Adaptations
in organisms
c) Species Not Evenly
Distributed
i. Australia,
Kangaroos, but
No Rabbits
ii. S. America,
Llamas
Darwin’s Observations
• Both Living
Organisms & Fossils
collected
• Fossils included:
•Trilobites
•Giant Ground
Sloth of South
America
This species NO longer existed.
What had happened to them?
Vocab
• Extinct species = a species is no longer
living on this earth
– EX: the Dodo Bird
• Extant species = a species that is currently
living and reproducing on earth
Definition
• Evolution is the
slow , gradual
change in a
population of
organisms over
time
Darwin’s Observations
• Left unchecked, the number of
organisms of each species will
increase exponentially
(overproduction
• In nature, populations tend to
remain stable in size
• Environmental resources are
limited (competition)
• Only the best-suited organisms
survive (survival of the fittest)
LIMITING FACTORS keep
populations in check
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Food or water
Competition for mates
Space (spreads disease)
Presence or absence of antibiotics
Change in temperature/ climate
Darwin’s Conclusion
• Production of more
individuals than can be
supported by the
environment leads to a
struggle for existence
among individuals
• Only a fraction of
offspring survive each
generation
• Survival of the Fittest
Darwin’s Big Ideas
• Overproduction
– More offspring are produced than can survive
• Competition
– Resources are limited; competition ensues
• Survival of the Fittest
– Only the individuals best suited for their
environment will survive and reproduce
Darwin’s Observations
• Individuals of a
population vary
extensively in their
characteristics with no
two individuals being
exactly alike.
• Much of this variation
between individuals is
inheritable.
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
• Acts on phenotype
Darwin’s
Theory of
Evolution
•The unequal ability of individuals to survive
and reproduce leads to a gradual change in a
population, with favorable characteristics
accumulating over generations (natural
selection)
•New species evolve (SPECIATION)
Natural Selection
1. Individuals vary within a species
2. Individuals compete for resources in the
struggle for existence
3. Fitness is the ability of an individual to
survive and reproduce in its
environment
Natural Selection cont.
4. Fitness is the result of adaptations
5. Adaptations are inherited characteristics
or traits that increase an organisms ability
to survive (or increase fitness)
6. Adaptations can be physical OR
behavioral
7. Individuals that are most fit are able to
survive and reproduce - “survival of the
fittest.”
Natural Selection cont.
8. Natural Selection – results in changes in
the inherited characteristics of a
population. These changes increase a
species’ fitness in its environment
Over Time, natural selection
results in changes in the
inherited characteristics of a
population. These changes
increase a species’ fitness in
its environment.
How Evolution Works
Artificial Selection
• nature provides variation, humans select
variations that are useful.
• Example - a farmer breeds only his best
livestock
Artificial Selection: Roses
III. Descent with Modification
• Each living species has
descended with
changes from other
species over time
IV. Evidence of Evolution
1. Fossil Record
2. Biogeography (Geographic Distribution
of Living Species)
3. Anatomical Homologies (Similar Body
Structures)
4. Developmental Homologies (Similarities
in Embryology)
5. Molecular Homologies (Similarities in
DNA sequences)
Evidence of Evolution
A. Fossil Record
Fossils are preserved remains of
ancient organisms
By comparing fossils from older
rocks with fossils from younger
layers, could see life on Earth
has changed over time.
Darwin view the fossil record as
a record of evolution while
others in his time only viewed
them as preserved remains.
Evidence of Evolution
B. Biogeography:
Geographic
Distribution of Living
Species
–
Different
environments contain
similar organisms with
distinct differences.
Ex. Flying squirrel (N.
America) and sugar
glider (Australia)
– Alfred Wallace
Evidence of Evolution
C. Homologous Body
structures
–
Structures that have different
mature forms but develop from
the same embryonic tissues
e.g. Wing of bat, human arm, leg of turtle
–
Turtle
Ancient
lobefinned
fish
vestigial organs– traces of
homologous organs from other
species having no apparent
function
e.g. Appendix (digest cellulose), pelvic girdle
in whales
–
Alligat
or
Bird
recapitulation- structures lost
during development
e.g. Gill slits
http://cas.bellarmine.edu/tietjen/Ec&Ev_Distance_learning/Evidence/evidence_pix.htm
Mammal
Ontogeny recapitulates
phylogeny
• ontogeny is the process of embryo
development (from the Greek onto,
meaning "being" or "existence" and genesis
meaning "origin")
• phylogeny is a species' evolutionary history
(from the Greek phyla, meaning "tribe" and
genesis meaning "origin")
Homologous Structures
Evidence of Evolution
D. Developmental
Homologies:
Similarities in
Embryology
–
In their early stages of
development, chickens,
turtles and rats look
similar, providing
evidence that they
shared a common
ancestry.
Evidence for Evolution - Comparative Embryology
Similarities In Embryonic Development
E. Molecular Homologies: Similar DNA
sequences
• Organisms in the same taxonomic
categories share similar DNA sequences
and proteins.
Patterns of Evolution
• Charles Darwin understood that evolution was a
slow and gradual process. Still, if evolution is
gradual, there should be a fossilized record of
small, incremental changes on the way to a new
species. His conclusion was that the fossil record
lacked these transitional stages because it was
incomplete.
• In 1972, evolutionary scientists Stephen Jay
Gould and Niles Eldredge proposed another
explanation, which they called "punctuated
equilibrium."
Gradualism and Punctuated
Stephen Jay
Gould and
Niles
Eldredge
Summary of Darwin’s Theory:
Evolution by Natural Selection
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Variations occur within populations, and some
of the variations are favorable.
More offspring are produced than can possibly
survive
Organisms compete for resources and
individuals with favorable variations are more
likely to survive.
Natural Selection causes species to changes
over time.
Species alive today are descended with
modification from ancestors
Survival of the Fittest!