Transcript Evidence for Evolution

Evidence for Evolution
ORGANIZE YOUR THOUGHTS!
EVIDENCE FOR EVOLUTION
 The Fossil Record
 Radiometric Dating
 Morphology
 Homology
 Molecular Biology
 Biogeography
 Analogous Structures
 Direct Observations
Evidence for Evolution – The Fossil Record
Evidence for Evolution
There is
overwhelming
evidence that living
species evolve from
organisms that are
extinct.
Evidence for Evolution – The Fossil Record
• What are fossils?
– Fossils are the
petrified remains of
ancient objects.
– Petrified – means
turned to stone.
– Ancient – means very,
very old.
• Paleontologist: Scientist
that studies fossils
Fossil Record
 The fossil record refers to the order in which fossils
appear within layers of rock that mark the passing of
geologic time.
Evidence for Evolution – The Fossil Record
•FOSSIL RECORD
•Fossils form when an
organism becomes buried
in mud, volcanic ash, or
sediments
•Over time the organic
remains become replaced
with inorganic minerals
Evidence for Evolution – The Fossil Record
• Fossils offer the most
direct evidence that
evolution takes place
– A record of Earth’s past
life-forms
– Change over time can be
seen in the fossil record
– Darwin predicted that
intermediates would be
found
Evidence for Evolution – The Fossil Record
–Fossil intermediates that
have been found:
• Fishes and
amphibians
• Reptiles and birds
• Reptiles and
mammals
• Tiktaalik
.
 Radiometric dating is the
method used most often to
determine absolute ages for
fossils.
 Organisms accumulate
radioactive isotopes when
they are alive, but
concentrations of these
isotopes decline after they
die.
 The rate of conversion is
indicated as the half-life
 the time it takes for 50%
of the isotope to decay.
Absolute Dating
 While carbon-14 is useful for
dating relatively young fossils,
radioactive isotopes of other
elements with longer half-lives
are used to date older fossils.
 While uranium-238 (half life
of 4.5 billion years) is not
present in living organisms to
any significant level, it is
present in volcanic rock.
 If a fossil is found sandwiched
between two layers of volcanic
rock, we can deduce that the
organism lived in the period
between the dates in which
each layer of volcanic rock
formed.
Absolute Dating
Morphology
•
Comparative anatomy
– Describes two kinds of
structures that contribute
to the identification of
evolutionary relationships
among species.
– Compares external
morphology and internal
anatomy
Evidence for Evolution - Homology
•
•
In the context of biology, homology is the existence of shared
ancestry between a pair of structures, or genes, in different species.
Homologous traits of organisms are therefore explained by descent
from a common ancestor
Evidence for Evolution - Homology
Why use the same skeletal plan for these very different appendages?
Evidence for Evolution – Homologous Structures
develop from similar tissue in embryological development
• Similar in various
species – provides
strong evidence
that all four-limbed
vertebrates have
descended, with
modification, from
common ancestors
Evidence for Evolution – Vestigial Organs
 Vestigial organs:
organs with no
apparent function
or purpose imply
evolutionary
relationships to
primitive ancestors.
• The structure served a purpose
in an ancient ancestor but no
longer does.
Evidence for Evolution – Vestigial Organs
• Vestigial
Organs in
Humans
EVIDENCE FOR EVOLUTION –
Molecular Biology
All living things share
the same genetic code.
 Nucleotide and amino
acid sequences of
DNA and proteins
from different species.
 Closely related species
share higher
percentages of
sequences than
distantly related
species.


Why should different
organism possess related
genes?
Molecular Data and the Evolutionary
Relationships of Vertebrates
• More than 98% of the nucleotide sequences in humans and
chimpanzees are identical.
EVIDENCE FOR EVOLUTION Biogeography
Geographic
distribution of species
has revealed that
unrelated species in
different regions of
the world look alike
when found in similar
environments.
PATTERNS OF EVOLUTION
• Parallel Evolution
– Two related
species making
similar
evolutionary
changes after
their divergence.
– Marsupial and
Placental
mammals
Patterns for Natural Selection
• Convergent Evolution – when two species
look alike but do not have a common
ancestor
• Similar in appearance
• Similar in function
• Different in development, origin, &
anatomy
Opossum
Aye-Aye
EVIDENCE FOR EVOLUTION
Analogous Structures
 body parts that resemble
one another in different
species, not because they
have evolved from a
common ancestor
 they evolved these
similar adaptations
independently because
they evolved in similar
environments with the
same selection pressures.
Similar solutions to similar problems
Analogous Structures
–Examples: wings of bird, bat & insects are analogous structure
EXAMPLES OF
CONVERGENT
EVOLUTION
EVIDENCE FOR EVOLUTION –
Direct Observation
Evolution of pesticide
resistance in response to
selection.
Evidence for Evolution
– Evolution Observed
PHYSIOLOGICAL
ADAPTATIONS
Evolution of antibiotic
resistance in response to
selection.
What Industries should be worried about resistance?
Evidence for Evolution –Drug Resistance
Heterozygote Advantage
Hypothesis:
In malaria-infected cells,
the O2 level is lowered
enough to cause sickling
which kills the cell &
destroys the parasite.
• The recessive sickle-cell allele produces hemoglobin with
reduced capacity to carry oxygen
• This mutation also confers malaria resistance in heterozygotes
• This heterozygote advantage leads to a larger proportion of the
recessive allele than usual in areas where malaria is widespread
• These populations exhibit balanced polymorphism between the
mutant and wild-type alleles