Evidence for Evolution
 We
will see numerous examples of
populations evolving in which they show
change over time during the course of the
semester.
 However,
I want to also discuss various
other pieces of evidence that evolution has
occurred.
 The
process of evolution implies that
organisms have an evolutionary history.
 Organisms
were not created as they are
today, but instead developed and changed
over time. This is what Darwin called
“descent with modification”
 Also,
implicit in evolutionary theory is the
idea of common ancestry i.e. that
organisms share common ancestors and
share traits because they inherited them
from their ancestors.
Evidence for an evolutionary
history
 Possession
of vestigial structures
atavistic structures and jerry-rigged
structures imply an evolutionary history.
 Fossils
also provide evidence of
evolutionary history.
Vestigial structures
 Many
organisms possess rudimentary or
functionless versions of body parts that
would have functioned in their ancestors.
 Cave
populations of Mexican tetra fish
have eye sockets but no eyes.
 Kiwis have tiny, stubby wings
 Some snakes and whales have tiny
remnant hind limbs
Kiwi clip
 https://www.youtube.com/watch?v=go52m
HlKDEo
Python spurs (remnants of hindlimbs)
http://etb-whales.blogspot.com/2012/03/snake-evolution-photos-ofvestigial.html
Human vestigial structures
 Coccyx:
vestigial tailbone at base of spine.
 Arrector pili muscle at base of hair follicles
makes hair stand up.
 Appendix: reduced in size. Used in
digestion of cellulose in herbivores e.g.
rabbits.
Vestigial developmental trait
 Adult
chickens: three bones in forefoot
(wing), four in hindfoot.
 However, digit 5 appears briefly during
embryonic development before
disappearing.
 In humans during embryonic development
a coat of hair (called lanugo) appears and
then usually disappears before birth
Lanugo
www.babyfaq.info
Molecular vestigial traits
 Human
genome contains large numbers of
pseudogenes that do not code for
functional RNA or proteins.
 E.g.
several pseudogenes of hemoglobin.
May be as many as 6,000 pseudogenes in
human genome.
Atavistic structures





We contain DNA instructions for making many
structures our ancestors possessed, but these
genes are usually turned off.
Sometimes these genes are accidentally turned
on and atavistic structures occur, which are
“throwbacks” to our ancestral state.
Examples : Extra toes in horses.
Tails in human
Hind limbs in whales and dolphins
http://trueorigins.us/atavisms2/4581821436
http://trueorigins.us/atavisms1/4581821435
Bottlenose dolphin atavistic hindlimbs
http://medicaldictionary.thefreedictionary.com
/polydactyly
Jerry-rigged (sloppily built)
structures
 Jerry-rigged
(sloppily built) structures e.g.
the Panda’s thumb.
 Natural
selection unlike an engineer or
designer does not build from scratch.
 Instead
it must use whatever materials are
available to it and modify them for new
purposes.
Panda’s have
[count them]
5 digits
But they also have a sixth digit a “thumb”’
 Panda
uses this “thumb” to hold bamboo
when eating.
 The
thumb is actually a wrist bone (the
radial sesamoid) that is found in all bears
but has become enlarged in pandas.
http://www.athro.com/evo/pthumb.html
Panda’s thumb
 The
panda’s thumb is not a very efficient
solution to the problem of holding bamboo,
but clearly suggests evolution rather than
design.
Other examples of shoddy
design-human eye
 The
retina of the human eye is wired
backwards. The photoreceptors face away
from the light.
 Its
blood and nerve supply lie between the
light source and the retina.
Human eye
 This
results in blood vessels interfering
with the passage of light and a blind spot
where the blood vessels and nerves exit
the eye.
Recurrent laryngeal nerve
 Recurrent
laryngeal nerve. The left
recurrent laryngeal nerve innervates the
larynx from the vagus nerve (10th cranial
nerve) .
 It
takes a very roundabout path to the
larynx as it loops under the aorta and then
back up to the larynx.
"Recurrent laryngeal nerve" by Jkwchui - Based on drawing by Truth-seeker2004.
Licensed under CC BY-SA 3.0 via Wikimedia Commons http://commons.wikimedia.org/wiki/File:Recurrent_laryngeal_nerve.svg#mediaviewer/Fil
e:Recurrent_laryngeal_nerve.svg
Recurrent laryngeal nerve
 Why
the long indirect route? (about 15 feet
in giraffes).
 Consequences
of developmental
pathways inherited from fish ancestors.
http://www.todayifoundout.com/index.php/2011/09/how-fish-gills-work/
Recurrent laryngeal nerve
 Early
in human embryological
development brachial arches form in the
neck.
 Arches 4 and 6 give rise to some of the
major blood vessels.
 The 4th branch of the vagus nerve lies
behind the 6th brachial arch and as the
arch moves into the thorax the nerve has
to move with it.
Fossil evidence of evolution
 Clear
from fossil evidence that many (in
fact almost all that have ever existed)
species have become extinct.
Fossil evidence of evolution
 Law
of Succession: Fossil and living
organisms in same area are related to
each other and differ from organisms in
other areas.
 The fact that recent fossils found in
continents resemble contemporary
organisms is of course consistent with the
current fauna having evolved in place.
 E.g.
Australia filled with marsupials, fossils
are of similar marsupial forms.
 South America contains both fossil and
living armadillos
Extinct glyptodont (2,000 kg) resembles
modern-day armadillo (2 kg). South America.
Modern Australian grey kangaroo (top) and
fossil kangaroos (below)
Pleistocene “giant” koala
and modern koala (above)
Fossil evidence of evolution
 Transitional
forms
 If fossil organisms are ancestors of
modern organisms then there should be
transitional fossils that show
characteristics intermediate between older
and more recent groups.
Archaeopteryx
 Archaeopteryx
the oldest known fossil bird
(name means “ancient wing) has mix of
reptilian and avian features.
 Reptilian:
long tail, teeth, long clawed
fingers
 Avian:
feathers, ribs with uncinate
processes, avian shoulder girdle.
Archaeopteryx
(oldest known
fossil bird)
Jurassic
150mya
Jaw evolution in mammals
 In
the distant ancestor of mammals known
as the synapsids the jaw was made up of
an anterior tooth-bearing dentary with a
series of bones (the post-dentary bones)
forming the posterior half.
 In
this condition the articular bone of the
lower jaw articulated with the quadrate
bone of the skull.
http://www.bbc.co.uk/nature/life/Synapsid
Synapsids
Jaw evolution in mammals
 In
modern mammals however the dentary
articulates with a skull bone called the
squamosal.
 How
did we transition from one articulation
articular-quadrate to the other dentarysquamosal?
Jaw evolution in mammals
 Our
ancestors could not have gone
through a “no articulation” phase.
 Organisms
cannot get less well adapted to
later become better adapted.
 What
do you predict must have happened
in the proto-mammal jaw?
Jaw evolution in mammals
 There
had to have been two jaw joints at
one point.
 We
have clear fossil evidence of this.
Jaw evolution in mammals
 In
a group of synapsids called the
cynodonts a process of the dentary grew
back and eventually made contact with the
squamosal bone of the skull.
 This
contact eventually formed the
dentary-squamosal joint. These animals
also had an A-Q joint.
Cynodonts
Evolution of dentary-squamosal joint
http://beta.revealedsingularity.net/content/articles/mammal_ear/images/jaw_artic.png
Jaw evolution in mammals
 Later
the original (A-Q) joint was lost, and
the jaw was reduced to a single bone the
dentary articulating with the squamosal
bone of the skull.
 Some of the post-dentary bones (incus,
malleus and stapes) came to form part of
the inner ear .
Whale evolution
 Whales
are aquatic mammals that evolved
from terrestrial ancestors.
 The
evolution of whales is well
documented by fossil discoveries.
Fossil whales
 Modern
whales have peg-like teeth or
baleen for feeding.
http://cimioutdoored.org/whale-teeth-vsbaleen/
http://designeranimals2011.wikispaces.co
m/killer+whale
 Early
fossil whales such as Dorudon (40
mya) however had more complex teeth
that were similar to those of contemporary
terrestrial mammals.
Dorudon
 Dorudon
and modern whales share
numerous features of the skull in common,
including a distinctive thick-walled
ectotympanic bone.
 The
same distinctive bone is found in
Pakicetus a terrestrial carnivorous animal
from 50 mya.
Pakicetus
 Pakicetus
also possesses a distinctive
ankle bone called the astragalus.
 In
Pakicetus it has a double-pulley like
morphology and this structure is found
only in artiodactyls (hoofed mammals such
as cows, pigs and deer).
Fossils reveal links to land mammals
• Shape of astragalus connects whales to artiodactyls
 These
and other fossil discoveries have
enabled biologists to construct a
phylogentic tree (a tree of branching
relationships) that depicts the evolutionary
history of the group.
Evidence of common ancestry.
Homologous structures
 Structures
constructed from the same
basic components.
 Forelimbs of human, mole, horse, dolphin
and bat contain the same bones, but used
in radically different ways.
 This makes no sense if organisms were
created, but does if organisms share a
common ancestor.
Homologous structures (i.e. derived from a common ancestor). Even though the
forelimbs have evolved to carry out very different tasks they are all constructed
from the same bones.
FIG 2.11
Developmental Homology
 Embryos
of diverse array of vertebrates
very similar in early development
Convergent Evolution

Not all similarities are due to homology.
 Streamlined shapes of fish and whale not a
result of common ancestry but of convergent
evolution.
FIG 2.12.
Convergent evolution
 Convergent
evolution means the same
evolutionary solution to a problem has
develops independently in unrelated
lineages.
 E.g.
Flying squirrels in Africa, U.S. and
Australia
http://www.nature.ca/notebooks/english/flys
quir_p8.htm. Northern flying squirrel
(Glaucomys sabrinus). U.S. (above)
Australian sugar glider Petaurus breviceps
(marsupial) right.
http://www.larsfoto.se/en/gallery/bird-images-from-foreigntrips/ghana/6414-pels-flying-squirrel?res=768. African flying
squirrel Anomalurus.
Molecular Homology
 With
few exceptions all organisms use
same genetic code.
http://plato.stanford.edu/entries/information-biological/
Molecular Homology
 Chromosome
17 in humans PMP22 gene
has duplicate sequence of DNA (CMT1A
repeat) on either side of it.
 Result
of duplication and insertion of DNA.
 Occasionally
causes inaccurate crossing
over during meiosis.
Molecular Homology
 Humans
share CMT1A repeat with
bonobos and chimpanzees, but not
gorillas, orang-utans or other primates.
 Suggests
CMT1A derived from common
ancestor of bonobos, chimps and humans.
http://theleagueofreason.co.uk/viewtopic.php?f=24&t=11401&start=20
Chromosomal homology
 Humans
have 23 pairs of chromosomes,
but chimps, and other great apes have 24.
 If
humans and the other great apes share
a common ancestor how is this possible?
 https://www.youtube.com/watch?v=8FGYz
ZOZxMw
 Centromere:
portion of chromosome that
link sister chromatids during cell division
 Telomere:
protective cap at the end of a
chromsome
Chromosome 2
 Chromosome
2 resulted from the fusion of
two chromsomes.
 Evidence
for this is that ch 2 contains two
centromeres instead of the usual one as
well as telomeres in the interior of the
chromosome.
Biogeographic evidence for
evolution: adaptive radiation
 Many
remote islands have unique floras
and faunas.
 They
are populated by arrays of diverse
but closely related organisms.
 This
is a result of process of adaptive
radiation
Adaptive radiation
 Ancestral
colonist arrives on island.
 Shortage
of resident species means many
niches are unfilled so no competition.
 Ancestral
species give rise to many
species that occupy unfilled niches.
Adaptive radiation
 Examples:
Darwin’s finches on
Galapagos Island, Drosophila on Hawaiian
Islands.
Darwin’s Finches
 On
Galapagos Islands there are 13
species of anatomically very different, but
closely related species of finch.
 They
differ greatly in beak size and diet
having evolved very different lifestyles.
Hawaiian Drosophila
 More
than 25% of the world’s Drosophila
fruit flies occur only in the Hawaiian
Islands.
 There
are few insect competitors so
original colonizers diversified to fill a large
number of niches.
If faunas created, why are woodpecker finches,
but not woodpeckers found on the Galapagos?