Evidence for evolution
 In
the early 1800’s prevailing belief was
that:



organisms were specially created and
unchanged since their creation
Species created independently of each other
Earth not old. Ussher’s estimate: for Earth’s
creation 4004 BC
Lamarck
 Fact
of evolution proposed in late 1700’s
early 1800’s.
 Jean Baptiste Lamarck 1809, 1815
proposed that all species were derived by
gradual evolution from other species.
 Lamarck’s idea was that evolution was
driven by an innate tendency of organisms
to become more complex over time.
Inheritance of Acquired
Characteristics
 Lamarck’s
proposed mechanism of
evolution was called the Inheritance of
Acquired Characteristics (IAC)
 IAC
suggested that modifications to
organisms during their life could be
passed on to their offspring (e.g., a giraffe
stretching its neck during its life passes
slightly longer neck to offspring).
Inheritance of Acquired
Characteristics

Obviously, Lamarck’s ideas about the
mechanism of evolution largely contradict
current biological knowledge.

The information required to build a body is
stored in DNA and that information (influenced
by the environment) determines the phenotype.
Changes to the phenotype during life however
do not affect the DNA sequence. Information
flow is thus only in one direction from DNA 
phenotype, not in the reverse direction.
Epigenetics
 However,
recent research in the emerging
field of epigenetics shows that Lamarckian
effects may occur through changes in the
control of gene expression caused by
environmental effects e.g. food shortage
during development.
Epigenetics

Epigenetics is the study of heritable changes in
gene expression caused by mechanisms other
than changes in the DNA sequence.

The DNA nucleotide sequence is not changed
but whether and how much genes are
expressed can be altered and some of these
changes may be passed from one generation to
another.
Epigenetics

One way in which epigenetic effects have been
shown to occur is through environmentally
induced methylation in which a methyl group
(CH3) is added to cytosine nucleotides
converting them to 5-methyl-cytosine.

More heavily methylated regions are translated
and transcribed less frequently than nonmethylated regions.
Epigenetics

One well documented example of epigenetic effects
resulted from the Dutch winter famine of 1944/45 at the
end of WWII.

The children of women pregnant during the famine were
born smaller than normal (which was to be expected).

However, the children of those children were also born
smaller than average. This suggests the famine induced
epigenetic changes in mothers pregnant during the
famine that were passed to their offspring.
Charles Darwin
published
“On the origin
of species”
in 1859.
Charles Darwin (1809-1882)
 Son
of a wealthy doctor.
 Dropped out of medical school.
 Studied theology, but was much more
interested in natural history (e.g. he had a
large insect collection).
 After college signed on as captain’s
companion on The Beagle.
Voyage of the Beagle
Darwin companion for Captain Fitzroy on
Voyage of The Beagle (1831-1836).
 The Beagle’s mission was to map the
coast of South America, but the ship
traveled around the World.
 Sites visited included Galapagos Islands
a group of volcanic islands (hence of
recent origin) off the coast of Ecuador.

Unique animals on Galapagos include
giant tortoises, marine iguanas, and
Darwin’s finches.
Galapagos Giant Tortoise
Sharpbeaked
Ground
Finch
Influence of geological thinking on
Darwin
 By
the time of “The Beagle” voyage the
idea that Earth was young was being
challenged.
 Opposition based on principle of
Uniformitarianism.
 This is the idea that geological processes
happening today are the same as have
operated in the past.
Influence of geological thinking on
Darwin
 Uniformitarianism
contrasted with
Catastrophism which proposed that
current geological formations had resulted
from catastrophic events (such as the
biblical flood) which occurred on scale
unknown today.
 Uniformitarianism
first proposed by James
Hutton and championed by Charles Lyell.
Influence of geological thinking on
Darwin
 During
the voyage Darwin read Lyell’s new
book “Principles of Geology.”
 Lyell emphasized two points:
 1. Gradualism: Geological features can
be explained by the slow gradual action of
processes we observe every day e.g.
erosion by wind and water, deposition of
sediments in rivers.
 2. The Earth is very old: there has been
lots of time for change to occur.
Influence of geological thinking on
Darwin
 Hutton
and Lyell inferred Earth must be
very old based on measurements of rate
of ongoing rock forming processes (e.g.
deposition of mud and sand).
 These
developments in geology focused
Darwin on the potential importance of
gradual change in shaping structures.
What Darwin observed
 On
the voyage Darwin noted many things
that were puzzling from the point of view of
a creationist explanation for the diversity of
life.
What Darwin observed





1. South American fossils resembled living South
American animals.
2. Parts of the world with similar habitats and
climates (e.g. Australia and South America) are
populated by very different animals.
3. Plants and animals on each continent are
different from those on other continents.
4. Many species on remote oceanic islands are
found only there (endemic).
5. Endemic species on islands closely resemble
species found on adjacent mainland.
What Darwin observed

These observations taken together don’t make
sense if organisms were specially created.



Why should similar habitats in different parts of the
world have different faunas?
Why should remote islands have unique faunas that
differ from but resemble those on adjacent land
masses?
Together these observations suggested to
Darwin that species change over time i.e., that
evolution occurs.
Darwin and Wallace

After returning from the voyage Darwin spent more than
20 years developing his ideas and gathering the evidence
to support them.

In 1858 Charles Darwin and Alfred Russel Wallace jointly
proposed natural selection as the primary mechanism by
which evolution takes place.

In 1859 Darwin published his book On the Origin of
Species, which summarized his ideas about evolution and
presented the evidence to support them.
The “modern synthesis”

Idea of evolution was accepted rapidly by
scientists.
 Lack of understanding of heredity and
population genetics, however, prevented natural
selection being accepted as the principal
mechanism of evolution until 1930’s.
 The “Modern Synthesis” in the 1930’s of
combined the ideas of population genetics and
natural selection to explain gradual evolution,
speciation, and macroevolution.
Evidence for Evolution
 Evidence
of change in organisms over
time
 An example in a living species:



evolution of beak length in soapberry bugs.
Soapberry bugs use long beak to penetrate
seeds in fruits and eat them.
Native host plant is balloon vine which has
thick fruits.
Evolution of Soapberry Bugs
 In
1926 flat-podded Golden rain tree
introduced to Florida. Has thin fruits.
 Today soapberry bugs feeding on Golden
rain trees have much shorter beaks than
those living on balloon vines.
Comparison of beak
lengths in areas
with and without
golden rain trees
Data from museum
specimens documents
change in beak length
over time.
Antibiotic resistance in bacteria

In 1947 only four years after the mass
production of penicillin began resistant strains of
Staphylococcus aureus began to be reported.

Antibiotic resistance is now widespread and in
the US half of all S. aureus infections are
resistant to multiple antibiotics including
penicillin, tetracycline, erythromicin and
methicillin.
Antibiotic resistance
 Bacteria
have evolved resistance quickly
in part because of their rapid reproduction,
but also because antibiotics were misused
(e.g. by being overprescribed or
prescribed for non-bacterial infections and
by people not completing their course of
antibiotics)
The evidence for evolution





Fossil evidence
Vestigial structures
Homologous structures
Atavistic structures
Other evidence



Jerry-rigged structures
Adaptive radiation
Artificial selection
Fossil evidence
 Fossils
are mineralized copies of the
remains of organisms preserved in
sedimentary rocks.
 In
the process of fossilization a dead
organism is covered by sediment and the
organic matter is replaced by minerals
leaving behind an impression of the
organism.
Fossil evidence of evolution
 Millions
of fossils have been collected and
it is clear from fossil evidence that many
species (in fact almost all that have ever
existed) have become extinct.
 Equally
clearly the faunas of different
geological eras are very different and have
changed over time.
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.
 South America contains both fossil and
living armadillos
Extinct glyptodont (2,000 kg) resembles the
modern-day South American armadillo (2 kg).
Fossil evidence of evolution
 Similarly
modern Australia is filled with
marsupials and fossils in Australia are of
similar marsupial forms.
 Extinct
short-faced kangaroo.
http://msnbcmedia2.msn.com/j/msnbc/Components/Photos/061226/061226_kangaroo_v
med_1p.widec.jpg
Fossil evidence of evolution
 Transitional
forms
 If fossil organisms are ancestral to modern
organisms then there should be
transitional fossils that show
characteristics intermediate between the
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
Evolution of mammals

There are numerous excellent fossil series that
document the transitions from ancestral species
to later species.

For example: the evolution of mammals from
synapsid reptiles.

An extensive series of fossils documents the
changes in the synapsid lower jaw from a jaw
made of multiple bones to the modern mammals
single dentary and the incorporation of some
synapsid jaw bones into the inner ear.
www.mun.ca/biology/scarr/142019_QA_to_DS_jaws.jpg
http://www.talkorigins.org/faqs/comdesc/images/jaws2.gif
Tiktaalik roseae

Another example is the evolution of the first
amphibians from lobe finned fishes.
 The transitional fossil Tiktaalik roseae
possesses an intermediate suites of characters.
 It has fish-like scales, palate and jaws, but an
amphibian-like mobile neck and head, an ear
that could hear in air, and the bones in its fins
are intermediate between those of fish such as
Eusthenopteron and Panderichthys and early
amphibians such as Acanthostega.
Tiktaalik roseae 375 mya
Figure 25.01a
http://images.google.com/imgres?imgurl=http://www.bringyou.to/apologetics/SynapsidRe
ptileMammal.jpg&imgrefurl=http://www.bringyou.to/apologetics/p15.htm&usg=__xL62Y1i
gePmktGVlxKZ_0QKqfxo=&h=617&w=489&sz=118&hl=en&start=3&um=1&itbs=1&tbnid
=pvmoIlV49CGugM:&tbnh=136&tbnw=108&prev=/images%3Fq%3Dsynapsid%2Bto%2
Bmammals%2Bjaw%2Bevolution%26hl%3Den%26sa%3DG%26um%3D1
Vestigial structures
 Many
organisms possess rudimentary or
functionless versions of body parts that
function in close relatives/ancestors.
 The
fact that structures are rudimentary
implies they had ancestors in which these
structures were functional. This suggests
an evolutionary history.
Examples of Vestigial structures
 Cave
populations of Mexican tetra fish
have eye sockets, but no eyes.
 Kiwis have tiny, stubby wings
 Boas have tiny remnant hind limbs
http://news.nationalgeographic.com/news/2006/02/images/060217_kiwi.jpg
Mexican Tetra
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 traits
 Adult
chickens: three bones in forefoot
(wing), four in hindfoot.
 However, digit 5 appears briefly during
embryonic development before
disappearing.
Molecular vestigial traits
 Human
genome contains large numbers of
pseudogenes that do not code for
functional RNA or proteins. These are
leftovers from evolutionary history once
functional genes that have been turned off.
 E.g.
there are several pseudogenes of
hemoglobin. May be as many as 6,000
pseudogenes in human genome.
Homologous structures

Homologous structures are those constructed
from the same basic components which have
been inherited from a common ancestor and
then modified for different purposes.

E.g. The forelimbs of a human, mole, horse,
dolphin and bat are constructed from the same
bones, but the bones differ in size and shape
and the structures made from the bones are
used in radically different ways.
Homologous structures
 Homologous
structures make no sense if
organisms were specially created, but they
do if a set of organisms share a common
ancestor and all inherited the same basic
bone structure from that ancestor.
 Homologous
structures imply an
evolutionary history and common ancestry.
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
Homology vs. Convergent
Evolution

Not all similarities between different species are due to
homology.

The streamlined shapes of sharks and whales are not a due to
common ancestry but to convergent evolution.

The same selection pressures to be able to swim efficiently in
water have independently produced similarly shaped bodies
instead of the traits being inherited from a recent common
ancestor.
Homology vs. Convergent
Evolution

Whales and dolphins evolved from terrestrial
ancestors about 50 million years ago, whereas
shark fossils as much as 350 million years old
are known.

The whales are most closely related to
artiodactyls (hoofed mammals that include deer
and hippos) and both whales and deer evolved
from hoofed, carnivorous ancestors.
http://static.howstuffworks.com/gif/great-white-shark-1.jpg
www.seaworld.org/.../images/
killer-whale.jpg
Homologous vs. Analagous
structures
 Similarly,
the wings of butterflies and birds
are not homologous (because their
structural components were not derived
from a recent common ancestor) but
perform the same function.
 Such
structures are analagous. They carry
out the same function.
Molecular Homology

All organisms (with a few minor exceptions) use
the same genetic code to specify which
sequences of bases specify which amino acids
when assembling proteins.

The reason the code is essentially universal is
that a mutation that altered the code would alter
almost every protein produced and so would be
lethal.
Figure 1.1.1. The standard genetic code and known variant nuclear codes.
(1) Candida, a unicellular yeast. (2) Micrococcus. (3) ciliated protozoans and green algae.
(4) Mycoplasma. (5) suppressor codon in bacteria. (6) Euplotes.
(7) the selenocysteine codon (8) Spiroplasma. (9) Micrococcus.
(10) resume codon in ssrA RNA (Lehman 2001).
http://www.talkorigins.org/faqs/comdesc/section1.html
Molecular Homology: Genetic flaws
shared by different species
 Chromosome
17 in humans PMP22 gene
has duplicate sequence of DNA (CMT1A
repeat) on either side of it.
 It
is the result of duplication and insertion
of DNA and 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.
Atavistic traits
 Atavistic
traits are anatomical
“throwbacks” that occasionally occur when
a feature present in an ancestor reappears
in a modern organism.
 For
example, occasionally horses are born
that have additional toes either side of
their hoof. Similarly, sometimes people
are born with a short tail.
http://atheistzoo.blogspot.com/2010/10/atavisms-blast-from-past.html
Atavistic traits
 Such
oddities are due to errors in
development that cause ancestral traits
normally suppressed in the genome to be
expressed.
 The
presence of genes for such traits
indicate an evolutionary history.
Atavistic traits
 The
embryos of a diverse array of
vertebrates are very similar in early
development.
 Atavistic
traits such as gill slits and a
postanal tail, which are not present in the
adult appear briefly before disappearing
later in development.
Other evidence for evolution: jerryrigged structures
 Jerry-rigged
structures e.g. the Panda’s
thumb.
 In
pandas, a wrist bone has been modified
into a “thumb” that is used to grip bamboo
stalks and assist in stripping leaves.
 The
“thumb” is not a very efficient solution
to the problem of bamboo stripping.
http://www.athro.com/evo/pthumb.html
http://www.athro.com/evo/pthumb.html
Panda’s Thumb

Natural selection must work with the material
available to it. Process is more like someone
tinkering in their workshop and assembling an
object from spare parts than an engineer building a
structure from scratch.

The jerry-rigged nature of the panda’s “thumb”
implies pandas were not designed, but evolved.
Other evidence for evolution:
adaptive radiation
 Adaptive
radiation and clusters of species.
 Many
remote islands are populated by
morphologically diverse clusters of closely
related species.
 This
pattern is difficult to explain without
evolution.
Process of adaptive radiation
 Ancestral
colonists arrive on island.
 Shortage
of resident species means many
niches are unfilled.
 Ancestral
colonizing species gives 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 1,250
species of Drosophila fruit flies found on
Hawaiian Islands.

Few insect competitors so Drosophila
have diversified to fill large number of
niches.
If faunas were created why are
there woodpecker finches, but no
woodpeckers on the Galapagos
Islands?
Artificial Selection

Artificial Selection. Humans as the agents of
selection have selectively bred for desirable
traits in domestic animals and plants for
thousands of years.

The tremendous diversity of body forms that
have been produced in domestic dogs in very
few generations show how quickly organisms
can change in response to selection.
Tameness in silver foxes

One excellent example of artificial selection is
Dimitri Belyaev’s work to breed tame Silver
foxes.

In each generation he bred only from the tamest
individuals and in only six generations was able
to produce foxes that were eager for human
contact and behaved like domestic dogs rather
than foxes.
Tameness in silver foxes

After about 30 generations 70-80% of the
experimental population displayed extreme
tameness.

In addition many foxes lots their fox-like look,
became piebald and resembled Welsh collies.
These were side-effects of selection for
tameness (an example of pleiotropy: genes
having more than one effect).
Silver fox after multiple generations of
selection for tameness (upper left)
http://www.nature.com/scitable/nated/
content/42740/Belyaev_foxes_MED.jpg
Creationism and “Intelligent
Design”

The idea of evolution has been harshly criticized
by religious fundamentalists since the
publication of the Origin in 1859.

This has been especially true in the U.S.

Repeatedly, believers in the literal truth of the
Bible have attempted to have alternatives to
evolution (i.e., creationism) taught in the public
schools and to have the teaching of evolution
either banned or restricted.
Creationism and “Intelligent
Design”
 The
U.S. Supreme Court has prohibited
the teaching of creationism in public
schools as a violation of the establishment
of religion clause of the Constitution.
 Latest
attempt to insert creationism into
schools is the idea of “Intelligent Design.”
Creationism and “Intelligent
Design”

The concept of “intelligent design” is outlined
most clearly in Michael Behe’s book “Darwin’s
Black Box.”

The central idea in “intelligent design” is that
some structures in the body are so complex that
they could not possibly have evolved by a
gradual process of natural selection. These
structures are said to “irreducibly complex.”
Creationism and “Intelligent
Design”
 By
“irreducibly complex” Behe means that
a complex structure cannot be broken
down into components that are
themselves functional and that the
structure must have come into existence in
its complete form.
Creationism and “Intelligent
Design”
 If
structures are “irreducibly complex”
Behe claims that they cannot have
evolved. Thus, their existence implies
they must have been created by a
designer (i.e. God, although the designer
is not explicitly referred to as such).
Creationism and “Intelligent
Design”
 Behe’s
main examples are various
biochemical pathways in the body, the
blood clotting system, and structures such
as the bacterial flagellum.
Creationism and “Intelligent
Design”
 Since
the publication of Behe’s book, it
has been demonstrated repeatedly that
things he has claimed to be irreducibly
complex are not in fact so.
 E.g.
the flagellum in eel sperm lacks
several of the components found in other
flagella, yet the flagellum functions well.
Creationism and “Intelligent
Design”
 The
blood clotting system in dolphins lacks
at least one component that the human
system has, yet it too is functional.
 In
addition, plausible gradual scenarios for
the evolution of biochemical pathways
including the Kreb’s cycle have been
documented.
Evolution of complex structures
 The
evolution of complex structures, such
as the eye, appears difficult, but natural
selection achieves this by the slow
accumulation of minor improvements from
one generation to the next.
Evolution of complex structures

Each step on the evolutionary pathway from a
simple light sensing cell to a complex eye
capable of focusing and producing color vision,
must be beneficial to the organism that possess
it and a slight improvement on earlier versions.

It is not necessary for a structure to be perfect or
even very good, it just needs to be better than
the alternatives to be favored by selection.
Variation in mollusc eyes from (a) pigment spot to (b) pigment cup to
(c) simple optic cup in abalone to (d) complex lensed eyes in a marine snail and
octopus.
Evolution of complex structures
 Computer
simulations suggest that eyes
can evolve easily and in nature eyes have
evolved independently more than 40
times.