Common Ancestry

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Common Ancestry
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Evolution
The idea that species slowly change over time as
a result of natural selection was proposed by
Charles Darwin. Evolving means to slowly change,
so this idea is called the theory of evolution.
Charles Darwin
HMS Beagle
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Most scientists believe that all forms of life
can trace their origins back to a single common
ancestor.
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Scientists believe that all of the species alive
today share a common ancestor. They theorize
that populations adapted to different
environments, and they changed over time into the
great diversity of life that we observe today.
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Common Ancestry
We show the relationships between different
species using cladograms and phylogenetic trees.
Both of these instruments show these
relationships in a very similar way.
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Common Ancestry
Different species that are more closely related
have a much more recent common ancestor.
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Common Ancestry
Scientists use evidence that they uncover in
fossils, studying biogeography and investigating
homologous structures (anatomical, molecular, or
developmental) to draw conclusions about the
relatedness of organisms.
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Common Ancestry
Fossils can help us study organisms that are now
extinct as well as about the history of an
ecosystem. By studying the fossils, we can learn
about what species that are alive today might be
related to the extinct species.
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The Fossil Record
Fossils can be used to study the ancestors of a
species. By studying the sequence of fossils
found in layers of rock, scientists can make
observations about how species have changed over
time.
Change Evolution
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Fossil of archaeopteryx
Artists Rendering of archaeopteryx
The study of fossils has led many scientists to
theorize that birds can trace themselves back to
a common ancestor that was a dinosaur.
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The Fossil Record
The fossil record is not complete, and there are
sometimes gaps between species. Because of this,
there are two major theories about the rate of
evolution based on the fossil record.
Punctuated Equilibrium
Gradualism
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The Pace of Evolution
Gradualism describes evolution as a process of
slow and continuous change. Populations are
gradually changing over time into new species.
Gradualism
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The Pace of Evolution
Punctuated equilibrium describes evolution as
having long periods of stability that are
interrupted by geologically brief periods of
significant change.
Punctuated Equilibrium
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The Pace of Evolution
When the populations are stable, they are in
equilibrium. These periods are punctuated by
periods of great change.
Punctuated Equilibrium
Rapid Change
Period of Stability
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Gradualism vs. Punctuated Equilibrium
There is evidence to support both of these
theories, and scientists believe that there may
have been times when evolution occurred according
to both of these theories.
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Gradualism vs. Punctuated Equilibrium
We depict these processes differently to suggest
the different rates. Gradualism shows the slow,
gradual changes with winding lines while
punctuated equilibrium is depicted with rapid
change followed by straight periods of stability.
Punctuated Equilibrium
Gradualism
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Homologies are similar structures in different
species that were derived from a common ancestor.
These homologous structures are studied to
determine the relatedness of species. These
homologies can be anatomical, molecular, or
developmental.
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Porpoise
Human
Bird
Elephant
Some animals have similar anatomy in their limbs,
but use their limbs for different purposes.
However, it is similar structure that shows
common ancestry. The different functions of
these limbs is due to natural selection.
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Common Ancestry
Comparing the DNA sequences of different species
provides some of the best evidence for common
ancestry. Because proteins are made from genetic
information, comparing amino acid sequences also
provides great evidence.
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Common Ancestry
Two species are more related when their molecular
structures are more alike. The species which are
more alike most likely have a more recent common
ancestor.
Cytochrome C is a mitochondrial protein found in
most eukaryotic organisms. It is compared across
species to determine the relatedness of different
species.
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Common Ancestry
Human embryos have gill slits and tails, and
this suggest that humans have a common ancestor
with other animals species that still have these
traits.
Different species can also display homologies in
their development. Embryology provides evidence
of homologous structures that often cannot be
observed in the fully developed organisms.
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It is homologous structures that provide the best
evidence for evolution. Using this evidence,
scientists construct diagrams to show
evolutionary relationships between species.
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Phylogenetic Tree
Cladogram
Species with a more recent common ancestor are
more closely related to each other, and this
would be evidenced by a greater number of
homologous structures.
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Common Ancestry
Fossils provide evidence that the continents were
once joined together in a supercontinent called
Pangea.
Biogeography is the study of the distribution of
species around the earth. By studying the
species that live in an area now (and in the
past), scientists can study how species have
changed and how they might be related.
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Biogeography
The field of biogeography has identified several
large zoogeographic regions that are separated
from each other by geographic boundaries such as
mountain ranges, broad deserts or oceans.
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Biogeography
Species in a region are isolated from other
regions and have been able to become adapted to
their own region over a long period of time.
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Charles Darwin, who first proposed the theory of
evolution, studied the distribution of finches on
the Galapagos Islands. Darwin concluded that the
different species came from a common ancestor,
and the differences between the species were a
result of natural selection.