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Fossils Indirect
The Law of Superposition
What early scientist is responsible for
these two important contributions to
evolutionary science?
Most Complex
The first fossilized fish appear
buried below the first fossilized
amphibians which appear below
the first fossilized reptiles
which appear below the first
fossilized birds and mammals.
Consistent with
Darwinian model of
Most Primitive
The second line of fossil
evidence for evolution
concerns transitional fossils.
Transitional fossils are fossils which
document the evolutionary change,
or transition, of one species into
The Mesohippus,
Merychippus, and Pliohippus are all
thought to be transitional fossils,
documenting the evolution of the
Eohippus into the modern horse.
Perhaps one of the most famous
“transitional fossils” of all time was the
archaeopteryx, which shows evidence of
transitioning between a reptile and a bird.
What is the difference between indirect and
direct evolutionary evidence?
Give an example of direct evidence, and of
indirect evidence of evolution.
How can the law of superposition be used
with fossil evidence to show that organisms
Give and example of, and describe how
transitional fossils are evidence of evolution.
Science sees structural similarities as evidence
that organisms evolved from a common ancestor.
Structural features with a common evolutionary
origin are called homologous structures.
All vertebrates
contain homologous
structures, and
therefore, come
from a common
Homologous parts are
similar in structure,
but may be very
different in function.
The body parts of organisms that do not have a
common evolutionary origin but are similar in
function are called analogous structures.
Analogous parts are
very different in
structure, but
perform similar
functions. They are
NOT evidence of
Another type of body feature that suggests
an evolutionary relationship is a vestigial
structure. These are structures that used to have a
function, but no longer do.
Why is discussion of analogous structures
inappropriate when detailing evidence of
How are homologous structures evidence of
Give an example of a human vestigial
structure, and describe why it is evidence of
Embryology is the study of organisms in
embryonic stages. The embryo is one of the
earliest stages of growth and development
of both plants and animals.
It is the shared features
in these vertebrate
embryos that suggests
evolution from a distant
common ancestor.
Shared Common Features:
• a tail posterior to the anus
• spinal cord
• muscles arranged in bundles
• cartilaginous, dorsal
notochord (what will become
the vertebral column in
• Pharyngeal gill slits
The biochemistry (DNA) of a bat is
much closer to that of a whale, than
that of a bird.
Not expected unless bat and whale
have a more recent common ancestor
than bat and bird, but evolution
predicts this. Why?
The same technology used to determine
paternity can be done to determine
shared ancestry.
Because bats and whales are mammals!
In one of the most extensive studies
comparing human and chimp DNA, the
researchers compared 19.8 million bases.
While this sounds like a lot, it still
represents slightly less than 1% of the
genome. They calculated a mean
similarity of 98.77% or 1.23% difference
Humans can be made temporarily immune to
certain diseases by receiving antibodies
produced in a horse’s body.
Physiology is the study of
mechanical, physical, and
biochemical functions of
living organisms. Anatomy, of
course, studies structures
within organisms.
Studying physiological and
anatomical similarities, and
differences in organisms will
tell you how closely they are
The more similarities they
share, the more closely
related they are!
What are two shared embryological features
among all vertebrates?
Give one example of how shared
biochemistry is evidence of relatedness, and
can therefore be used as evidence of
How can comparative anatomy and
physiology can be used to show relatedness,
and therefore be used as evidence of
The Hardy-Weinberg model enables us to compare a
population's actual genetic structure over time
(microevolution) with the genetic structure we
would expect if the population were in, what we
call, Hardy-Weinberg equilibrium (or not evolving).
If allelic
shift at all from
one generation
to the next,
then evolution
is occurring.
Hardy-Weinberg Equilibrium maintains five
basic assumptions:
Each of
1. the population is infinitely large, and that genetic
drift is not an issue within the population.
2. there is no gene flow, or migration in or out of
the population
3. mutation is not occurring
4. all mating is totally random
5. natural selection is not occurring
these five are
by which
Selection is
not the
Under these conditions it is obvious that evolution would
not occur. There are no mechanisms of evolution acting on
the population, so the process cannot happen--the gene
pool frequencies will remain unchanged.
However, since it is highly unlikely that any one of
these five conditions, let alone all of them, will
happen in the real world, evolution is inevitable.
What are the five basic assumptions that
must be in place in order for the HardyWeinberg equilibrium to be maintained?
How can we use the Hardy Weinberg as
evidence that evolution is occurring?