Download Evidence for evolution

 Assigned
reading: chapter 2 of text
Natural vs. Supernatural
explanations
 All
societies have or had creation myths
that invoke the action of supernatural
forces to explain the origins of life and the
history of the earth.
 Ideas
invoking the role of gods and divine
actions are supernatural (i.e. beyond
nature).
In 1859 Charles Darwin published “On the origin of
species.”
Darwin and the origin
 In
“The Origin” Darwin presented a
detailed strongly, supported argument,
that life had originated naturally and that
over time organisms had evolved by
means of a mechanism he called natural
selection.
 How
did this transition from supernatural
to a natural explanation for the diversity of
life occur?
Development of Natural
Philosophy
 The
early Greeks were among the first to
develop natural philosophy to explain the
world.
 Natural
philosophers aimed to develop
sets of physical laws to explain the world
around them and how it worked.
Methodological Naturalism
 The
Greeks’ approach of trying to explain
the world using only natural phenomena is
sometimes called Methodological
Naturalism.
 Methodological because this strategy
provides a procedure or method for
scientifically explaining the world and
natural because it focused on nature.
Anaximander’s cosmology
 An
early example of methodological
naturalism is Anaximander’s cosmology
(p. 31 of text) . He proposed the earth is a
disk surrounded by huge wheels on which
the moon and sun rotate around the earth.
 His
explanation is mechanistic because it
invokes a natural (although incorrect)
mechanism to explain the presence and
motion of celestial objects.
Aristotle (384-322 BC)
 Aristotle
was the first Greek philosopher to
emphasize observation and the testing of
ideas to explain those observations (i.e.,
hypothesis testing).
 Supernatural explanations are inherently
untestable.
 The Greeks also emphasized the
importance of logic in moving from
observations to general principles.
An ancient and ever-changing
earth
 That
the earth is old and undergoes
constant change was not widely accepted
until recently in western thought.
 Most of Darwin’s contemporaries
considered the earth to be young (only
thousands of years old rather than 4.6
billion).
An ancient and ever-changing
earth
 By
time Darwin was a young man the idea
that the Earth was young was being
challenged.
 Opposition based on principle of
Uniformitarianism.
 Idea that geological processes happening
today are the same as have operated in
the past.
An ancient and ever-changing
earth
 Uniformitarianism
contrasted with
Catastrophism which proposed that
current geological formations had resulted
from catastrophic events (such as biblical
flood) which occurred on scale unknown
today.
 Uniformitarianism first proposed by James
Hutton and championed by Charles Lyell
in his books Principles of Geology.
An ancient and ever-changing
earth
 Hutton
and Lyell inferred the Earth must
be very old based on measurements of
rates 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.
The intellectual environment
 In
the early 1800’s the world was primed
for a comprehensive theory of evolution to
be developed.
 Multiple people put forward the idea that
evolution had taken place, what was
lacking was a workable mechanism.
 One influential scientist is this period was
Jean-Baptiste Lamarck.
Jean-Baptiste Lamarck
 In
1809 Lamarck suggested that
organisms descended gradually from older
less complex species. He considered
lineages of organisms had an inherent
tendency to become more complex over
time and transformed over time.
 His primary mechanism was called the
Inheritance of Acquired Characteristics
(IAC).
Inheritance of Acquired
Characteritics
 IAC
suggested that traits an organism
acquired during its life could be passed on
to its offspring. By this process of
transformation lineages would change
over time.
 For example, a giraffe stretching its neck
during its life would become slightly longer
necked and pass this slightly longer neck
to its offspring.
Inheritance of Acquired
Characteristics
 Lamarck’s
ideas were widely discussed
and influential in his time as there was no
understanding of how heredity occurs.
 Obviously, Lamarck’s ideas about
mechanism of evolution contradict current
biological knowledge.
 Information flows from DNA to phenotype
not in the reverse direction
Charles Darwin (1809-1882)
 Was
the son of a wealthy doctor, but he
himself dropped out of medical school.
 Studied theology at university, but was
more interested in natural history.
 After graduation signed on as the
Captain’s companion for a round the world
voyage aboard the surveying ship HMS
Beagle.
The Beagle Voyage
 On
the voyage Darwin read Lyell’s
Principles of Geology and was greatly
influenced by Lyell’s emphasis of two
major points .
 1. The Earth is very old.
 2. Geological features we see around us
can be explained by the action of the slow,
gradual processes we can observe every
day (e.g. the eroding of rock by waves and
wind; the slow deposition of sediment).
The Beagle Voyage
 Darwin
was Captain Fitzroy’s companion
during the voyage (1831-1836).
 The Beagle mapped the coast of South
America and circled the globe.
 Visited South America, Australia, Pacific
Islands and South Africa.
 Famously visited the Galapagos Islands a
group of volcanic (hence quite young
islands) off the coast of Ecuador.
Unique animals on Galapagos include
giant tortoises, marine iguanas, and
Darwin’s finches.
Galapagos Giant Tortoise
Sharpbeaked
Ground
Finch
The Beagle Voyage
 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 animals.
 2. Parts of the world with similar climates and habitats
(e.g. Australia, South America) populated by very different
organisms.
 3. Plants and animals on each continent are distinctive.
 4. Many species on oceanic islands are
found only there (endemic).
 5. Endemic species on islands closely resemble species
on adjacent mainland.
What Darwin observed

These observations taken together don’t make
sense if organisms are specially created. Why
should similar habitats in different parts of the
world have completely 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.,
evolution occurs.
Natural Selection
 Convinced
by the time he returned to
England that evolution occurs, Darwin
needed a mechanism to explain how
evolution happens.
 His
mechanism is the process of natural
selection.
Natural selection
 An
important event in developing natural
selection was when Darwin read Thomas
Malthus’ “Essay on population.”
 Malthus
emphasized that the reproductive
potential of animals and the rate at which
populations could increase in size was
much greater than the rate at which food
resources might increase.
Natural selection
 Darwin
realized that most organisms that
were born could not survive to reproduce.
There just were not enough resources.
 Thus,
there must be “a struggle for
existence” in which only some organisms
survived to reproduce and the remainder
did not.
Natural Selection
 Darwin
knew that individuals in
populations are different from each other
(there is variation).
 His insight was in realizing that if success
in surviving and reproducing was related
to variation (i.e. to the traits individuals
possessed) that beneficial traits would
become more common and populations
would change over time.
Darwinian Natural Selection
Artificial Selection
 Artificial
Selection. Humans have
selectively bred for desirable traits in
domestic animals and plants for millenia.
 Process has produced our crop plants,
garden plants, pets, and domestic
animals.
 Darwin closely studied pigeon breeding.
Pigeon breeding
 Pigeon
fanciers by selecting for particular
traits among Common Rock Doves by
breeding from only certain individuals had
been able to produce a huge variety of
different breeds of domestic pigeons.
 These varieties were so different in
appearance that they would have been
considered to be different species if
encountered in the wild.
Common Rock Dove
http://ibc.lynxeds.com/photo/rock-dovecolumba-livia/perched-my-balcony
Hungarian Buga
www.PigeonBreed.com
Holle Cropper
www.PigeonBreed.com
Pomeranian Pouter
www.PigeonBreed.com
Frillback Crested
www.PigeonBreed.com
Evolution by Natural Selection
 Darwin
envisaged a process similar to
artificial selection that had produced
organisms we see today. He called it
Natural Selection.
 Instead
of humans deciding who would
breed, nature would.
Evolution by Natural Selection
 Darwin
proposed evolution was the
inevitable outcome of 4 postulates:

 1.
There is variation in populations.
Individuals within populations differ.
 2.
Variation is heritable.
Evolution by Natural Selection
 3.
In every generation some organisms
are more successful at surviving and
reproducing than other. There is
differential reproductive success.
 4.
Survival and reproduction are not
random, but are related to variation among
individuals. Organisms with best
characteristics are ‘naturally selected.’
Evolution by Natural Selection
 If
these 4 postulates are true then the
population will change from one
generation to the next.
 Evolution will occur.
Darwin and Wallace
 Darwin
realized his ideas would be
controversial and delayed publishing them
for fear of the backlash that would result.
Instead he continued to gather evidence to
support his ideas.
 It was not until he received a letter from
Alfred Russel Wallace in 1858 in which
Wallace outlined the idea of natural
selection was Darwin finally prompted to
publish his work.
Darwin and Wallace
 1858
Charles Darwin and Alfred Russel
Wallace jointly proposed natural selection
as the mechanism of evolution in a paper
presented to the Royal Society.
 1859
Origin of Species published
The Modern Synthesis
 Idea
of evolution accepted rapidly
 Lack of understanding of heredity and
population genetics prevented natural
selection being accepted as mechanism
until 1930’s.
 “Modern Synthesis” of population genetics
and natural selection to explain gradual
evolution, speciation, and macroevolution.
Evidence for Evolution
 Evidence
of change in organisms over
time
 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.
Vestigial organs
 Many
organisms possess rudimentary or
functionless versions of body parts that
function in close relatives/ancestors
 Cave populations of Mexican tetra fish
have eye sockets but no eyes.
 Kiwis have tiny, stubby wings
 Boas have tiny remnant hind limbs
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.
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.
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 related to each
other and differ from organisms in other
areas.
 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).
Fossil evidence of evolution
 Transitional
forms
 If fossil organisms 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
180mya
Evidence of common ancestry.
Homologous structures
 Structures
constructed from the same
basic components.
 Forelimbs of human, mole, horse, dolphin
and bat constructed from same bones, but
used in radically different ways.
 Makes no sense if organisms specially
created, but logical 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

Not all similarities due to homology.
 Streamlined shapes of fish and whale not a
result of common ancestry but convergent
evolution.
FIG 2.12.
Molecular Homology
 With
few exceptions all organisms use
same genetic code.
 Genetic
flaws shared by species.
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.
Other evidence for evolution

Jerry-rigged structures e.g. The Panda’s
thumb.
Panda’s Thumb

In Pandas, a wrist bone modified as tool to strip
bamboo.
Panda’s “thumb” not very efficient solution to
Bamboo-stripping problem.


Natural selection must work with the material
available.
“Thumb” implies pandas not designed,
but evolved.

Other evidence for evolution

Adaptive radiation and clusters of
species.
Many remote islands populated by
diverse, but closely related species.

Adaptive radiation
 Ancestral
colonist arrives on island.
 Shortage
of resident species means many
niches are unfilled.
 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 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 created, why are woodpecker finches,
but not woodpeckers found on the Galapagos?
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.