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Scientific evidence to support the Theory
of Evolution by Natural Selection
• FOSSILS – are the
mineralized remains or traces
(tracks, imprints) of animals,
plants or other organisms
• THE FOSSIL RECORD –
fossils found in rock strata that
show a sequence or history of
life on Earth
Trilobite fossil found in
Burgess Shale
• The Burgess Shale is
a middle Cambrian
site (~540 MYA)
• One of the few places
in the world where
difficult-to-preserve
soft-bodied
organisms of our past
were preserved
Some of the fossils found here are
now long extinct and are unlike
anything presently existing
• Fossils found in young
layers of rock (ie closer to
the surface) tend to be
more similar to present
day organisms
• Fossils appear in
chronological order
(oldest ancestors in
deepest layers
• Not all organisms appear
in the fossil record at the
same time – ie fish are
the oldest vertebrates –
then in subsequent layers
amphibians, reptiles,
mammals and birds
• Transitional fossils
are fossils that show
intermediary links
between groups of
organisms
• They can provide a
link between the past
and present
Archaeopteryx – a transitional fossil
because of its characteristics of both
reptiles (dinosaurs) and birds
ARCHAEOPTERYX – transitional fossil
• Example: Basilosaurus and
Dorudon were ancient
whales with tiny hind limbs –
living entirely in water
• Ambulocetus – a more
recent ancestor, had heavier
leg bones and lived in both
water and on land
- The tiktaalik was an ancient tetrapod
- It was thought to have descended
from lobe-finned fishes
-- They lived in oxygen-poor water
- used their lobe fins to live partly on
land-possibly gave rise to amphibians
• Darwin and Wallace
observed that many
species evolve in one
location and spread
out to other areas
• Darwin found 14
different species of
finch – he theorized
all evolved from one
common ancestral
finch
ADAPTIVE RADIATION
– Diversification of a
common ancestral
species into a variety of
species
Close environments (ie
desert & forest in South
America) have more
related species than
geographically
separate but
environmentally similar
locations (ie – desert in
S.America, desert in
Australia)
-left: cactus from S.America
-right: cactus from Australia
Animals found in
islands often
resemble
animals found on
closest islands –
suggesting
animals have
evolved to suit
new environment
Example: lizards
off NW coast of
Africa (canary
islands are
similar to lizards
in West Africa
Top: Canary Island
lizard
Bottom: West African
lizard
• Fossils of the same
species can be found
on the coastline of
neighbouring
continents
• Example:
Cynognathus has
been found in Africa
and S.America
• At one time, all
continents were
joined (Pangea – 250
MYA)
-a depiction of the Earth 250 MYA –
continents were joined together
-distribution of ancient
organisms
Cynognathus crateronotus
Vertebrate forelimbs
can be used for many
different functions:
• Flying (birds, bats)
• Swimming (whales)
• Brachiation
(monkeys)
• Running-horses,dogs
HOWEVER: they ALL contain the
same set of bones organized in
similar ways – WHY?
Homologous structures are similar in
structure but often differ in function
Homologous structures provide
evidence for a common ancestor
amongst all vertebrates
Analogous Structures
Structures that evolve separately to
perform a similar function are
analogous. The wings of birds,
bats, and insects, for example,
have different embryological origins
but are all designed for flight.
•Bird: feathers
•Bat: skin
•Butterfly: chitin
VESTIGIAL STRUCTURES
• Vestigial structures
are thought to have
had a purpose at
one time in our
ancestry, but no
longer have a
specific function
(eg) human appendix
VESTIGIAL STRUCTURES
• “c” indicates the
Underdeveloped hind
legs
Of the baleen whale
• The muscles connected
to the ear of a human do
not develop enough to
have the same mobility
as those of the monkey
• The embryos of
different vertebrates
show similar stages
of embryonic
development
• Neck pouches – in
humans become ears
& throat
- in fish become gills
- Similarities among embryos point to a
common ancestor
Can you tell which
embryo is which?
A – cat
B – cow
C - horse
D - human
• Many organisms share
similar cellular
components such as:
• Proteins – long chains
of amino acids used for
building & repair
• Enzymes – made from
proteins – they control
many biochemical
reactions in the cell
• DNA – genetic material
found in the nucleus
The DNA of
chimpanzees & humans
is ~ 98% identical
• Hemoglobin—the oxygen-transport
protein that gives blood its red color—
got its start at about the time life
originated on earth, nearly four billion
years ago. Now it is almost ubiquitous,
appearing in the cells of plants, animals
and even bacteria, and a study of this
protein affords scientists a rare glimpse
back as well as forward in time. A look
at the ancestral hemoglobins indicates
that newly arising proteins co-opt the
chemistry of older ones and gain new
functions through structural alterations.
But these studies have revealed an
additional way to modify function.
Scientists are coming to the realization
that changes in a protein's regulation—
the when and how of its expression—
can also give rise to functional
differences. The surprise, says the
author, is that these regulatory changes
outpace structural ones—an important
lesson for students of molecular
evolution and a possible indicator of
where protein evolution will go in the
future.
http://adsabs.harvard.edu/abs/1999Am
Sci..87.....H
hemoglobin (found in
RBCs) is used to bond
to O2
Above: Hominid evolution