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.