Transcript 03 EvolutionEvidence

Evidence of Evolution
by Natural Selection
AP Biology
2007-2008
Dodo bird
Evidence supporting evolution
 Fossil record

transition species
 Anatomical record
homologous & vestigial structures
 embryology & development

 Molecular record

protein & DNA sequence
 Artificial selection

human-caused evolution
Fossil record
 Layers of sedimentary rock contain fossils
new layers cover older ones, creating a
record over time
 fossils within layers show that a
succession of organisms have populated
Earth throughout a long period of time

Fossil Record
Fossil record
 A record showing us that today’s organisms
descended from ancestral species
Evolutionary change in horses
550
500
Body size (kg)
450
Equus
400
350
300
250
Merychippus
200
150
Mesohippus
Hyracotherium
100
50
Nannippus
60 55 50 45 40 35 30 25 20 15 10 5 0
Millions of years ago
Evolution of birds
 Archaeopteryx


lived about 150 mya
links reptiles & birds
Smithsonian Museum,
Washington, DC
Land Mammal
?
?
?
?
2006 Fossil Discovery of Early Tetrapod
 Tiktaalik

“missing link” from sea to land animals
Study of Paleontology ( Three scientists)
Older sediments are below younger sediments.
Georges Cuvier (1769-1832)
2005-
Gradualism
 James Hutton (1726-1797)

Earth’s geologic features —
profound change formed as
product of slow but continuous
& cumulative processes
2005-
Uniformitarianism
Charles Lyell
(1797-1875)
geologic processes
have not changed
throughout Earth’s
history
 Conclusion: Earth
must be much older
than 6,000 years

2005-
II. Anatomical record
Looking at
morphological divergence
and
morphological convergence
morphological divergence
 Proof in Homologous structures
Have similarities in characteristics
resulting from common ancestry
 BUT Diverge into separate species

Homologous structures
 Similar structure
 Similar development
 Different functions
 Evidence of close
evolutionary relationship

recent common ancestor
Homologous structures
spines
leaves
succulent leaves
needles
colored leaves
tendrils
Example of Morphological
divergence (text)
 All modern vertebrates share a ‘stem
reptile’ who crouched low to the
ground (common ancestor)
 Descendents of this stem reptile
diversified in new habitats and became
bird, reptiles, mammals
 Its 5-toed limbs became many things
Stem reptile:
walked
crouching on
the land
Morphological convergence:
Proof: Analogous structures
 Separate evolution of structures
Look alike in different lineages
But…
 different internal structure &
development
 different origin
 no evolutionary relationship

Don’t be fooled
by their looks!
Solving a similar problem with a similar solution
Example of…Convergent evolution
 Flight evolved in 3 separate animal groups
evolved similar “solution” to similar “problems”
 Have analogous structures

Does this mean
they have a
recent common
ancestor?
Example of Convergent evolution
 Fish: aquatic vertebrates
 Dolphins: aquatic mammals
similar adaptations to
life in the sea
 not closely related

Those fins & tails
& sleek bodies are
analogous structures!
Parallel Evolution
 Convergent evolution in common niches


filling similar ecological roles in similar
environments, so similar adaptations were selected
but are not closely related
marsupial
mammals
placental
mammals
Parallel types across continents
Niche
Burrower
Placental Mammals
Australian Marsupials
Mole
Marsupial mole
Anteater
Numbat
Anteater
Nocturnal
insectivore
Mouse
Climber
Marsupial mouse
Spotted cuscus
Lemur
Glider
Stalking
predator
Chasing
predator
Sugar glider
Flying
squirrel
Ocelot
Tasmanian cat
Wolf
Tasmanian “wolf”
Vestigial organs
 Modern animals may have structures that
serve little or no function


remnants of structures that were functional in
ancestral species
deleterious mutations accumulate in genes for
non-critical structures without reducing fitness
 snakes & whales — remains of pelvis & leg bones of
walking ancestors
 eyes on blind cave fish
 human tail bone
This is not
LaMarck’s loss
from “disuse”!
Vestigial organs
 Hind leg bones on whale fossils
Why would whales
have pelvis & leg bones
if they were always
sea creatures?
III. Comparative embryology
 Similar embryological development in
closely related species

all vertebrate embryos have similar
structures at different stages of
development
 gill pouch in fish, frog, snake, birds, human, etc.
Similarity due to: Master Genes
(Homeotic genes)
 A set of genes that determine
development in the embryo
 Failure of one of these genes most
often leads to devastating results in
body plan
 These genes are highly ‘conserved’
meaning that they have not changed
over evolutionary time.
 Embryos of many
vertebrate species
develop in similar ways
 Example: All vertebrates
go through a stage with
four limb buds and a tail
Ex. Master Genes and Appendages
DLx gene expression
leads to appendages
So, what controls where
appendages grow on the body?
 HOX master gene
 When present, it suppresses the


activity of Dlx
Example: embryonic pythons – Hox is
expressed along the length of snake’s
body – no appendages.
Read about this on page 306
Molecular record
 Comparing DNA & protein structure

universal genetic code!
Why compare
these genes?
 DNA & RNA

compare common genes
 cytochrome C and b (respiration)
 hemoglobin (gas exchange)
Human/kangaroo
Closely related species have
sequences that are more similar
than distantly related species
 DNA & proteins are a molecular
record of evolutionary relationships
Nucleotide substitutions
100
Dog/
cow
75
Human/
cow
Rabbit/
rodent
50 Horse/
donkey
Llama/
cow
Horse/cow
Sheep/
goat
25
Human/rodent
Pig/
cow
Goat/cow
0
0
25
50
75
100
Millions of years ago
125
Comparative hemoglobin structure
Human Macaque
Dog Bird
Frog
Lamprey
32 45
67
125
Why does comparing
amino acid sequence
measure evolutionary
relationships?
8
0 10 20 30 40 50 60 70 80 90 100 110 120
Number of amino acid differences between
hemoglobin (146 aa) of vertebrate species and that of humans
DNA and amino acid sequence
differences...
...are greatest among lineages that
diverged long ago,
...and less among recently diverged
lineages
Comparing Cytochrome b Sequences
10 different species compared to the
Honeycreeper (bird)
Differences shown in red
They tend to be neutral mutations and
do not affect the overall sequence for
the cytochrome b protein
(found in cellular respiration)
Building “family” trees
Closely related species (branches) share same line of
descent until their divergence from a common
ancestor
What data from whole
genome sequencing can tell
us about evolution of humans
Example: the
Evolutionary Hypothesis
of Common Ancestry
Chromosome Numbers in
the great apes:
human (Homo)
chimpanzee (Pan)
gorilla (Gorilla)
orangutan (Pogo)
46
48
48
48
Testable prediction:
If these organisms share a common
ancestor, that ancestor had either
48 chromosomes (24 pairs) or
46 (23 pairs).
Testable prediction:
Common ancestor had
48 chromosomes (24
pairs) and humans carry
a fused chromosome; or
ancestor had 23 pairs,
and apes carry a split
chromosome.
Chromosome Numbers in
the great apes
(Hominidae):
human (Homo)
chimpanzee (Pan)
gorilla (Gorilla)
orangutan (Pogo)
46
48
48
48
Ancestral
Chromosomes
Fusion
Homo sapiens
Inactivated
centromere
Telomere
sequences
Centromere
Telomere
Human Chromosome #2 shows the exact
point at which this fusion took place
Homo sapiens
Inactivated
centromere
Telomere
sequences
Chr 2
“Chromosome 2 is unique to the human
lineage of evolution, having emerged as a
result of head-to-head fusion of two
acrocentric chromosomes that remained
separate in other primates. The precise fusion
site has been located in 2q13–2q14.1 (ref. 2; hg
16:114455823 – 114455838), where our analysis
confirmed the presence of multiple subtelomeric
duplications to chromosomes 1, 5, 8, 9, 10, 12, 19,
21 and 22 (Fig. 3; Supplementary Fig. 3a, region
A). During the formation of human chromosome 2,
one of the two centromeres became inactivated
(2q21, which corresponds to the centromere from
chimp chromosome 13) and the centromeric
structure quickly deterioriated (42).”
Hillier et al (2005) “Generation and Annotation of the DNA
sequences of human chromosomes 2 and 4,” Nature 434: 724 – 731.
IV. Artificial selection
 Artificial breeding can use variations in
populations to create vastly different
“breeds” & “varieties”
“descendants” of wild mustard
“descendants” of the wolf
Natural selection in action
 Insecticide &
drug resistance
insecticide didn’t
kill all individuals
 resistant survivors
reproduce
 resistance is inherited
 insecticide becomes
less & less effective

Evolution is "so overwhelmingly
established that it has become
irrational to call it a theory."
-- Ernst Mayr
What Evolution Is
2001
Professor Emeritus, Evolutionary Biology
Harvard University
(1904-2005)
2007-2008
Don’t be a Dodo…
Ask Questions!!
2007-2008