Grade 11 University Biology – Unit 3 Evolution
Structural Evidence for Evolution
Section 8.2 Page 332-340
Scientifically, we know the Earth formed about 4.5 billion years ago (BYA). The Christian biblical
interpretation of Earth’s formation is 6,000 years based on the stories describing events 4,000 years
before Christ and the 2,000 years hence. We have also estimated scientifically, according to the fossil
record, the first unicellular prokaryote appeared
between 3.8-3.5 BYA
Darwin’s achievement - He put together facts and
observations that seem previously related and
provided a theory that combines and explains life in a
geological time frame
Evidence of Evolutionary Theory
Fossil Record – The remains and traces of past life
that are found in sedimentary rock. The fossil record
reveals the history of life on Earth and the kinds of
organisms that were alive in the past.
The different periods are illustrated opposite and
Biology 11 (Page 333, Figure 8.5).
From this geological time scale and its fossil record,
we can see that some organisms have survived with
little change for many years, other organisms are the
ancestors of modern organisms, and some organisms
are extinct (…the trail ends with extinction).
The fossil record offers the following evidence:
 Fossil in upper layers (closer to the surface,
“younger” in time) are similar to the species
presently alive
 Fossil appear in chronological order in the rock
layers (…fossil of ancestors of species are found
in older rocks below the fossils of latter species)
 Not all organisms appear in the fossil record at
the same time. This suggests that some
organisms evolved from ancestral organisms.
The example is amphibians evolved from
ancestral fish, reptiles evolved from ancestral
amphibians, and both animals and bird evolved
from different groups of reptiles.
 Fossils provide direct evidence for changes in
life in rocks of different ages. The diagrammatic
skulls show the changes in the jaw articulation
and the ear region in the evolution from reptile to mammal. In reptiles, the lower jaw is made up of
several bones on each side and there is only one ear bone, the stapes, on each side. In
mammals, the lower jaw is made up of only one bone on each side and the other jaw bones have
taken on new functions in the middle ear. The reptilian articular bone becomes the malleus bone
of the middle ear of mammals and the quadrate bone of the reptilian jaw becomes the incus bone
of the middle ear of mammals. The angular bone is lost.
Transitional Fossils
 A fossil that shows intermediary links
between groups of organisms and
shares characteristics common to two
now separate groups.
 So…gaps exist in the fossil record.
Transitional fossils provide some
missing links.
 Vestigial Structures are structures that
are a reduced version of structures
that were functional in the organism’s
ancestors. As shown, the whale has a
femur and a pelvis. Yet, a whale does
not walk. These structures are not used in the modern whale. It is believed that the whale’s
ancestor was a terrestrial animal.
 See Figure 8.7 on Page 335 – Archaeopteryx: A Transitional Fossil
Can you identify the vestigial structures in the following species…using human as the base?
Biogeography
 Study of the past and present geographical distribution of different populations
 Darwin (…and Wallace…) hypothesized that species evolved in one location, and then, spread to
other regions. Darwin’s finches are an example. Darwin thought an ancestral finch evolved far
from the Galapagos Islands, and …somehow… migrated to the islands. Since the islands were
separate and the food resources on each island were also different, each finch evolved to
possess favourable traits to use the food resources on a particular island.
 The idea of biogeography is supported by the following evidence:
 Geographically close environments (i.e., in close proximity to one another) are more likely
to be populated by related species
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Animals found on islands often resemble animals on the nearby continent. In other
words, island species evolved from mainland migrants. Over time, the island dwellers
adapted to the island’s environmental conditions
Fossils of the same species
can be found on the
coastline of neighbouring
continents. As we know,
the continents drift. At one
time in geological history,
the continents were joined.
For example, Africa and
South America were one
joined super-continent
(Gondwana) about 510
million years ago. When
they drifted apart, similar
species occurred on either
continent (see Figure 8.8 on Page 335 of Biology 11).
Closely related species are almost never found in exactly the same location or habitat.
Anatomy
 Homologous Structures – Structures
that have similar structural elements
and origin, but they may have a
different purpose.
 Using the diagram, all organisms
illustrated have a humerus bone and a
carpal bone. As each organisms
adapted to its unique behavioural and
environmental conditions, the bones
began to perform different functions and
look structurally different.
 NOTE: Homologous structures can be
similar in structure, function or both.
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Analogous Structures – Structures of
organisms that do not share a common
evolutionary origin but perform similar
functions.
 Analogous structures evolve in species
of different origin who live in similar
ecological units. In your own words,
what does this mean?
 Analogous structures are structures that
are look and act very similar to one
another. Yet, they evolved separately to
perform a similar function. For an
example, wings on insects and wings
on bats have different ancestral origins, but both use their wings to fly. The wings are
superficially similar, but they serve the same purpose.
Analogous Structures arise from Convergent Evolution, the process in
which two distinct lineages evolve a similar characteristic
independently of one another. This often occurs because both
lineages face similar environmental challenges and selective
pressures.
Embryology
 The study of early, pre-birth stages of an organism’s
development
 It is used to explore and determine
evolutionary relationships between
different animal species. Embryos of
different organisms exhibit SIMILAR
STAGES of embryonic development.
 The similarities between embryos in
related groups (e.g. vertebrates) suggest
the groups shared a common ancestral
origin. Logically, related species share
some adult features (e.g., forearm bone
structure arrangement)
 In the illustration, all the embryos, in their
earliest stage (top of the illustration)
exhibit a tail extending behind the anus;
yet by the latest stage shown, the tails are
distinctly different or missing completely.
 As well, all early embryos have paired
pouches just beneath their “heads.” What
do you think these pouches becomes in a
fish and humans?
DNA
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Evolutionary relationships between species are present in their genes. DNA carries all the
genetic information. By comparing DNA from different species, you can determine how closely
they are related. If two species have similar DNA patterns, the two species must have inherited
the genetic information from a common ancestor at some point in evolutionary history.
DNA information supports our empirical observations (e.g., fossil records, anatomy,
biogeography)
HOMEWORK
 Page 340, Questions 3, 5, 6, 8, 11, 15
For more information and a very useful Internet tour, see Welcome to Evolution 101 at
http://evolution.berkeley.edu/evolibrary/article/evo_01