Transcript in natural selection

Charles Darwin (1809-1882)
Sailed around the world 1831-1836
Darwin found…many unique species
How did tortoises and birds differ among
the islands of the Galapagos?

Each island
had its own
type of
tortoises
and birds
that were
clearly
different
from other
islands
Galapagos
Turtles
What did Darwin’s
Travels reveal?

The diversity of living
species was far
greater than anyone
had previously
known!!

These observations
led him to develop the
theory of evolution!!
What do you think evolution is?
or
What do you think “evolution”
means?
Turn to a partner and discuss.
Evolution is when organisms change over time. So,
modern organisms descended from ancient ones
Convergent Evolution
Species exposed to the
same selective pressure
in different parts of the
world tend to develop
the same adaptations
 Even though they may
be completely unrelated
 e.g. the placental wolf
and the marsupial
thylacine or Tasmanian
wolf

© 2008 Paul Billiet ODWS
Thylacine Thylacinus cynocephalus
Wolf Canis lupus
Convergent evolution led to mimicry

Why do these pairs look so similar?
Monarch male = poisonous
fly
bee
Viceroy male = edible
moth
bee
Divergent Evolution
Populations of a species that are
separated and evolve under different
selective pressures develop different
adaptations as they diverge
 They are usually geographically separated
so that there is a barrier to the mixing of
genes

© 2008 Paul Billiet ODWS
Evidence supporting evolution

Fossil record


shows change over time
Anatomical record

comparing body structures
 homology
& vestigial structures
 embryology & development

Molecular record


comparing protein & DNA sequences
Artificial selection

human caused evolution
1. Fossil record
 Layers
 new
of rock contain fossils
layers cover older ones
 creates
a record over time
 fossils
show a series of organisms have
lived on Earth
 over
a long period of time
Fossils tell a story…
Primate Fossils
Australopithecus
Homo erectus
Homo sapien
Relative vs.
Absolute
Dating
Relative Dating
Can determine a
fossil’s relative age
 Performed by
estimating fossil age
compared with that
of other fossils
 Drawbacks –
provides no info
about age in years

Absolute dating
Can determine the
absolute age in
numbers
 Is performed by
radioactive dating –
based on the amount
of remaining
radioactive isotopes
remain
 Drawbacks - part of
the fossil is destroyed
during the test

Carbon-14 Dating
2. Anatomical record
Animals with different
structures on the surface
But when you look under
the skin…
It tells an evolutionary story
of common ancestors
Homologous structures

Structures that come from the same origin
 homo-
= same
 -logous = information

Forelimbs of human, cats, whales, & bats
 same
 on
structure
the inside
 same
development in embryo
 different functions
 on
the outside
 evidence
of common ancestor
Homologous Body Structures
But don’t be fooled by these…

Analogous structures
 look
 on
similar
the outside
 same
function
How is a bird  different structure & development
like a bug?
 on
the inside
 different
origin
 no evolutionary relationship
Solving a similar problem with a similar solution
Analogous structures
Dolphins: aquatic mammal
 Fish: aquatic vertebrate

 both
adapted to
life in the sea
 not closely related
Vestigial Organs
 traces
of homologous organs in other
species
 Organ that serves no useful function
e.g. Appendix
Vestigial organs

Hind leg bones on whale fossils
Why would whales
have pelvis & leg
bones if they were
always sea creatures?
Because they
used to
walk on land!
In your notes….

In one sentence, write your answer to
the following question…..
 What
is the difference between homologous
and analogous structures?
*Similarities in
Embryology
In their early
Stages of
development,
chickens, turtles
and rats look
similar, providing
evidence that they
shared a common
ancestry.
Embryological development
3. Molecular record

Comparing DNA & protein structure
 everyone
uses the same genetic code!
 DNA
 compare
common genes
 compare
common
proteins
number of amino acids
different from human
hemoglobin
Human
Macaque
Dog Bird
Frog
Lamprey
8
32 45
67
125
0 10 20 30 40 50 60 70 80 90 100 110 120
4. Artificial selection

How do we know natural selection can
change a population?
 we
can recreate a similar process
 “evolution by human selection”
“descendants” of wild mustard
Questions for you……

What do you think artificial selection is?

Do you think the use of artificial selection
is a “good thing?” Why or why not?
Artificial Selection
nature provides variation, humans select
variations that are useful.
 Example - a farmer breeds only his best
livestock

Selective Breeding
Humans create the
change over time
“descendants” of the wolf
Artificial Selection
…and the
examples keep
coming!
I liked
breeding
pigeons!
Artificial Selection gone bad!

Unexpected
consequences of
artificial selection
Pesticide resistance
Antibiotic resistance
Insecticide resistance
 Spray
but…
the field,
 insecticide
didn’t
kill all individuals
 variation
 resistant
survivors
reproduce
 resistance is
inherited
 insecticide becomes
less & less effective
Natural
Selection

The traits that
help an
organism survive
in a particular
environment are
“selected” in
natural selection
Natural Selection and Species
Fitness
Overtime, natural selection results in
changes in the inherited
characteristics of a population.
 These changes increase a species
fitness (survival rate)

Summary of Darwin’s Theory
1. Organisms differ; variation is inherited
2. Organisms produce more offspring than
survive
3. Organisms compete for resources
4. Organisms with advantages survive to
pass those advantages to their children
5. Species alive today are descended with
modifications from common ancestors
Any Questions??