Download Evolution . . . .

Evolution . . . .
What is evolution?
 The change of organisms over time.
 The mechanism is called natural selection.
Evidence of Evolution
 The fossil record: signs of organisms from past
times.
 We know that the Earth has been around for
nearly 4.6 billion years!
 Started with no life
 Very little O2
 No plants for photosynthesis
 Life evolved ~3.5 bya (billion years ago)
 This was most likely in the oceans because of
the harsh atmosphere.
 First organisms were prokaryotic.
The Fossil Record
 Types of fossils:
 Trace fossils- footprints, trails,
burrows.
 Casts- minerals in rock fill in space left
by organism.
 Imprints- objects leave an imprint in
sediment that later hardens.
 Petrified- minerals replace the hard
parts of an organism  creating a copy.
 Amber- entire organisms found in tree
sap.
 Molds- an organism is buried in
sediment and decays, leaving an empty
space.
How old are these things???
 Relative dating (not what
it sounds like!)
 Older fossils are
imbedded deeper in
rock layers than new
ones.
 Radiometric dating
 Using radioactive
isotopes of elements
that break down over
time  usually
“Carbon 14”.
Plate Tectonics
 The earth has plates of
land that have been
moving over the years.
 Single land-mass was
called Pangea
 Continents are still
moving.
Humans
 Modern humans appeared about 200,000 years
ago.
Evolution now . . .
 Charles Darwin most famous for his theory of Natural
Selection and his study of Galapagos finches.
 British biologist, traveled to the Galapagos Islands
 Researched animals there, especially the finches
 Darwin studied animals in the
Galapagos Islands to help
understand how species can
change over time.
 Darwin collected evidence for
22 years.
 Published evidence in his book
“Origin of Species” and
introduced the idea of Natural
Selection.
Struggle to Survive
 Darwin proposed that organisms struggle to
survive because they compete for:
 Food
 Space
 Mates
 They struggle to escape from predators
 Think of how organisms compete for food . . . .
 How do they compete for mates?
 What happens when an organisms loses these
competitions????
Natural Selection
 Survival of the Fittest!
 What is fitness in this case?
 An organism’s ability to survive and pass on its genes
to offspring.
 This does not necessarily mean the fastest and
strongest . . . . . Sometimes it can mean the sneakiest
is most fit.
Natural Selection
 Natural selection acts on individuals.
 Natural Selection occurs when individuals with certain
traits survive, reproduce, and pass on their genes to
future generations. (Remember inheritable traits!)
 Organisms without these traits may be less likely to
survive and reproduce.
 This results in the evolution of the species, or changes in
that species over time.
Natural Selection
 Requires 3 things!
1) Variation
2) Differential Reproduction
3) Heritability
Adaptations
 Adaptations are structures or behaviors that give
organisms a better chance of survival in their
environment.
 Adaptations can arise as a mutation in one
individual that allows it to survive better.
 That mutation will be passed on to offspring.
Structural Adaptations
 These are physical
characteristics that help an
organism survive.
 Sharp teeth  help to eat meat
 Long sticky tongue  helps to
catch insects
Structural Adaptations
 Mimicry: Allows one organism to look like another
(usually a nasty one!)
 Camouflage: allows organisms to blend in with their
environment. Why do you think this is good?
Peppered
Moths
http://www.ted.com/talks/david_gallo_shows_underwater_astonishments.html
A structural adaptation . . . .the Aye Aye
Darwin’s Finches
Misconception :“Evolution is a theory
about the origin of life.”
Misconception : “Natural selection
involves organisms ‘trying’ to adapt.”
Either an organism has genes that
enable its survival or it doesn’t.
Misconception : “Natural selection gives
organisms what they ‘need.’ ”
A population either has the ‘right’ variation or it doesn’t. If it
doesn’t, the population may die out.
Misconception : “Evolution is like a
climb up a ladder of progress;
organisms are always getting better.”
Mechanisms of Evolution
 Genetic Drift
 Gene Flow
 Artificial Selection
 Natural Selection
Sexual Selection
Genetic Drift
Change in allele
frequency by
CHANCE
Gene Flow
Change in allele frequency as
a result of MIGRATION
Artificial Selection
Humans choose desired traits and
manipulate breeding
Sexual Selection
 Special case of Natural Selection
 Variations selected for their ability to
attract a mate
 May the best man/animal win
The Lyre bird!
Selective Pressures
 Environmental characteristics that favor the survival of
certain organisms
 Examples: drought, lack of food, extreme temperatures,
predation
Sources of Variation
 GENE FLOW moves genes among populations
 SEXUAL REPRODUCTION introduces new gene
combinations
 Random MUTATIONS in DNA lead to the formation
of new alleles (sound familiar?)
Natural selection
affecting populations
Three major types of
natural selection are:
 Stabilizing Selection
 Directional Selection
 Disruptive Selection
Stabilizing selection
 Average individual is
selected for
Directional selection
One extreme trait is selected for
Disruptive Selection
Both extremes
are selected for
Average selected
against.
Can evolution produce
new species?
 Of Course.
Called “Speciation”
 This happens by two
major methods
1. Geographic isolation
2. Reproductive
isolation
Geographic isolation
 Physical barrier
divides a
population
 New selective
pressures
 Two different
species
Reproductive isolation
No longer able to
mate
Different genetic
information
Mating behavior
differences