Transcript Evolution by Natural Selection

Evolution by Natural Selection
Scientific Theory
 An explanation of natural phenomenon
supported by a large body of scientific
evidence obtained from many different
investigations and observations.
Evolution
 A gradual change in a species (populations) through
adaptations over time.
 Adaptation = some phenotypic feature or trait that
improves an organism’s likelihood of survival and
reproduction.
 In Georgia, there is a popular hunting area of forest
called the Poopycack forest, where the Poopy Deer
lives. This species of deer has 6 ears.
 How might this adaptation have occurred and how is it
beneficial?
 What would you expect to happen to the Poopy Deer
population in the next 1000 years?
Charles Darwin
“Theory of Evolution by Natural Selection”
 Proposed that new species
could develop through a
process called Natural
Selection
 During his travels aboard
HMS Beagle, made
numerous observations
and collected evidence
that led him to propose a
revolutionary hypothesis
about the way life changes
over time
Darwin’s Voyage
Darwin studied animal species in the Galapagos
Islands and found they each had unique
adaptations
Darwin’s Studies
 Galapagos finches demonstrate different
adaptations to eat different kinds of foods
 Galapagos tortoises are the biggest in the
world
Natural Selection
 Acts on Phenotype rather than Genotype
 Those better suited for their environment will survive
 Those least suited to their environment will die faster,
leaving fewer offspring
Genetic variation is essential!
Mutations
 _________ promote
genetic variation,
which helps ensure
a species survival
 Like crossing over!
How does a great number of
species ensure that at least
some organisms survive
major changes in the
environment?
 Those who are better at adapting will
survive major changes in the environment
Natural Selection
 A mechanism for change in a population
 Natural Selection (NS) is responsible for
most evolutionary change by selectively
changing genetic variation through
differentiated survival and reproduction.
 Goal - To be fit enough to survive and
reproduce
 Three types of NS
Stabilizing Selection
 Favors average
individuals in a
population
 Those individuals
have a “selective
advantage”.
 Reduces variation
in a population
Directional Selection
 Favors one of the extreme variations of a
trait
 Can lead to rapid evolution of a population
Disruptive Selection
 Favors both
extreme
variations of
a trait
 Leads to
evolution of
two new
species
Speciation
 A process of producing
two individual species
from one
 Members of the
population no longer
interbreed within their
natural environment
Evidence for Evolution:
 1. Fossil record
 A piece of organism or imprint left behind.
 Fossils show that species have changed over time.
 2. Vestigial structures
 Body structures that have shrunken and are not used anymore.
 3. Homologous structures
 Structures that share a common ancestry and look/behave
similarly.
 4. Embryology
 5. DNA homology, Amino Acid homology,
Mitochondrial DNA, Photosynthetic Plant cells
Evidence For Evolution
 Fossils
 Provide a
record of
early life and
evolutionary
history
Defining age of fossils!
Geologic Strata (sedimentary
layers) and Carbon Dating
 Carbon-14
(remember
isotopes?)
 Used to date any
object composed of
carbon
 Radioactive carbon
decays over time
 check amount of C14
left in sample,
enabling you to tell
age of object
 Did you know that whales have feet?
 Well, sort of….
Fossils help us determine whale evolution
60 million
years ago
50 million
years ago
40 million
years ago
Yesterday
Vestigial Structures
 Human tail-bone, wisdom teeth, appendix (they
have no purpose)
 Snake feet,
 Whale feet
Homologous Structures
(derived from a common ancestral feature)
means the same!
Limb adapted to function
Analogous
Structuressimilar in
function but
not structure
Evidence For Evolution
 Embryology
 Similarities among
the young embryos
suggest evolution
from a distant,
common ancestor
 Biochemistry
 Comparing DNA
and RNA
How do we know what happened
when?
 Radiometric dating relies on half-life decay of
radioactive elements to allow scientists to
date rocks and materials directly
 Stratiography provides a sequence of events
from which relative dates can be extrapolated
 Molecular Clocks allow scientists to use the
amount of genetic divergence between
organisms to extrapolate backwards to
estimate dates.
(Means the same!)
DNA/Amino Acid Homology
 Human
5’A-T-C-T-T-A-C-G-A-A-T-C-A-T-G-C-C-C-T-A-AC-T-T-C-G-G-C-A-T-T-A-C-G-C-T-A-G-C-3’
 Whale
5’A-C-C-T-T-A-C-C-A-A-T-C-A-T-T-C-C-C-T-A-AC-T-T-A-G-G-C-A-T-T-A-C-G-C-T-A-G-C-3’
 Frog
5’A-C-C-A-T-G-C-G-T-G-T-C-A-T-C-C-C-C-G-A-GC-T-T-C-G-G-T-A-T-T-A-C-G-C-A-A-G-C-3’
 Gorilla
5’A-T-C-T-T-A-C-G-A-A-T-C-A-T-G-C-C-C-T-A-AC-A-T-C-G-G-C-A-T-T-A-C-G-C-T-A-G-C-3’
Can you create a cladogram from the information above?
 http://www.youtube.com/watch?v=faRl
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