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Chapter 25 ~
Phylogeny & Systematics
Phylogeny: the evolutionary history of a species
• Systematics:
the study of biological
diversity in an
evolutionary context
• The fossil record:
the ordered array of
fossils, within layers,
or strata, of
sedimentary rock
The fossil record
• Sedimentary rock: rock
formed from sand and
mud that once settled on
the bottom of seas,
lakes, and marshes
•Dating:
•1- Relative~ geologic time
scale; sequence of species
•2- Absolute~ radiometric
dating; age using half-lives of
radioactive isotopes
Absolute Dating
Biogeography: the
study of the past and
present distribution of
species
• Pangaea-250 mya
√ Permian extinction
• Geographic isolation-180 mya
√ African/South
American reptile fossil
similarities
√ Australian marsupials
Mass extinction
• Permian
(250 million years
ago): 90% of
marine animals;
Pangea merge
• Cretaceous
(65 million years
ago): death of
dinosaurs, 50% of
marine species; low
angle comet
Phylogenetics
• The tracing of
evolutionary
relationships
(phylogenetic tree)
• Linnaeus
• Binomial
• Genus, specific epithet
• Homo sapiens
• Taxon (taxa)
Phylogenetic Trees
• Cladistic Analysis: taxonomic approach that classifies
organisms according to the order in time at which branches
arise along a phylogenetic tree (cladogram)
• Clade: each evolutionary branch in a cladogram
Types:
• 1- Monophyletic single ancestor that gives rise to all
species in that taxon and to no species in any other taxon;
legitimate cladogram
• 2- Polyphyletic members of a taxa are derived from 2 or
more ancestral forms not common to all members; does not
meet cladistic criterion
• 3- Paraphyletic lacks the common ancestor that would
unite the species; does not meet cladistic criterion
Constructing a Cladogram
• Sorting homology vs. analogy...
• Homology:
likenesses attributed to
common ancestry
• Analogy:
likenesses attributed to
similar ecological roles and
natural selection
• Convergent evolution:
species from different
evolutionary branches that
resemble one another due to
similar ecological roles
A Cladogram
Chapter VI
Chapter VI
Chapter VI
…Organs of extreme perfection and complication. -To suppose that the eye, with all its inimitable
contrivances for adjusting the focus to different
distances, for admitting different amounts of light,
and for the correction of spherical and chromatic
aberration, could have been formed by natural
selection, seems, I freely confess, absurd in the
highest possible degree.
…Organs of extreme perfection and complication. -To suppose that the eye, with all its inimitable
contrivances for adjusting the focus to different
distances, for admitting different amounts of light,
and for the correction of spherical and chromatic
aberration, could have been formed by natural
selection, seems, I freely confess, abserd in the
highest possible degree.
…Organs of extreme perfection and complication. -To suppose that the eye, with all its inimitable
contrivances for adjusting the focus to different
distances, for admitting different amounts of light,
and for the correction of spherical and chromatic
aberration, could have been formed by natural
selection, seems, I freely confess, abserd in the
highest possible degree.
Yet reason tells me, that if numerous gradations
from a perfect and complex eye to one very
imperfect and simple, each grade being useful to its
possessor, can be shown to exist; if further, the eye
does vary ever so slightly, and the variations be
inherited, which is certainly the case; and if any
variation or modification in the organ be ever useful
to an animal under changing conditions of life, then
the difficulty of believing that a perfect and complex
eye could be formed by natural selection, though
insuperable by our imagination, can hardly be
considered real. …
Yet reason tells me, that if numerous gradations
from a perfect and complex eye to one very
imperfect and simple, each grade being useful to its
possessor, can be shown to exist; if further, the eye
does vary ever so slightly, and the variations be
inherited, which is certainly the case; and if any
variation or modification in the organ be ever useful
to an animal under changing conditions of life, then
the difficulty of believing that a perfect and complex
eye could be formed by natural selection, though
insuperible by our imagination, can hardly be
considered real. …
Yet reason tells me, that if numerous gradations
from a perfect and complex eye to one very
imperfect and simple, each grade being useful to its
possesser, can be shown to exist; if further, the eye
does vary ever so slightly, and the variations be
inherited, which is certainly the case; and if any
variation or modification in the organ be ever useful
to an animal under changing conditions of life, then
the difficulty of believing that a perfect and complex
eye could be formed by natural selection, though
insuperible by our imagination, can hardly be
considered real. …
Chapter VI
Chapter VI
Chapter VI
…Organs of extreme perfection and complication. -To suppose that the eye, with all its inimitable
contrivances for adjusting the focus to different
distances, for admitting different amounts of light,
and for the correction of spherical and chromatic
aberration, could have been formed by natural
selection, seems, I freely confess, abserd in the
highest possible degree.
…Organs of extreme perfection and complication. -To suppose that the eye, with all its inimitable
contrivances for adjusting the focus to different
distances, for admitting different amounts of light,
and for the correction of spherical and chromatic
aberration, could have been formed by natural
selection, seems, I freely confess, abserd in the
highest possible degree.
Yet reason tells me, that if numerous gradations
from a perfect and complex eye to one very
imperfect and simple, each grade being useful to its
possessor, can be shown to exist; if further, the eye
does vary ever so slightly, and the variations be
inherited, which is certainly the case; and if any
variation or modification in the organ be ever useful
to an animal under changing conditions of life, then
the difficulty of believing that a perfect and complex
eye could be formed by natural selection, though
insuperable by our imagination, can hardly be
considered real. …
Yet reason tells me, that if numerous gradations
from a perfect and complex eye to one very
imperfect and simple, each grade being useful to its
possessor, can be shown to exist; if further, the eye
does vary ever so slightly, and the variations be
inherited, which is certainly the case; and if any
variation or modification in the organ be ever useful
to an animal under changing conditions of life, then
the difficulty of believing that a perfect and complex
eye could be formed by natural selection, though
insuperible by our imagination, can hardly be
considered real. …
Yet reason tells me, that if numerous gradations
from a perfect and complex eye to one very
imperfect and simple, each grade being useful to its
possesser, can be shown to exist; if further, the eye
does vary ever so slightly, and the variations be
inherited, which is certainly the case; and if any
variation or modification in the organ be ever useful
to an animal under changing conditions of life, then
the difficulty of believing that a perfect and complex
eye could be formed by natural selection, though
insuperible by our imagination, can hardly be
considered real. …
…Organs of extreme perfection and complication. -To suppose that the eye, with all its inimitable
contrivances for adjusting the focus to different
distances, for admitting different amounts of light,
and for the correction of spherical and chromatic
aberration, could have been formed by natural
selection, seems, I freely confess, abserd in the
highest possible degree.
Chapter VI
Chapter VI
Chapter VI
Chapter VI
Chapter VI
Chapter VI
Chapter VI
…Organs of extreme perfection and complication. -- To suppose that the
eye, with all its inimitable contrivances for adjusting the focus to
different distances, for admitting different amounts of light, and for the
correction of spherical and chromatic aberration, could have been
formed by natural selection, seems, I freely confess, absurd in the
highest possible degree.
Yet reason tells me, that if numerous gradations from a perfect and
complex eye to one very imperfect and simple, each grade being useful
to its possessor, can be shown to exist; if further, the eye does vary ever
so slightly, and the variations be inherited, which is certainly the case;
and if any variation or modification in the organ be ever useful to an
animal under changing conditions of life, then the difficulty of believing
that a perfect and complex eye could be formed by natural selection,
though insuperable by our imagination, can hardly be considered real.…
Charles Darwin, The Origin of Species
• The principle of parsimony states
that a theory about nature should be
the simplest explanation that is
consistent with the facts.
• Phylogenetic trees are hypotheses
• The strongest phylogenetic
hypotheses of all are supported by
both the morphological and
molecular evidence.