Download Homologous

http://www.johnkyrk.com/evolution.html
Palaeontology
• Life has existed for
more than 500 million
years
• Very different than
today
• None of the top
predators we have
around today were
around at the time of
the dinosaurs
Fossils as evidence for evolution
• First organisms were simple in structure
(matches the expected sequence)
• Life forms have increased in size and
complexity
• Life forms are constantly changing
• Evolutionary dead ends
• Punctuated equilibrium vs gradualism
Palaeontology
many living organisms
today have no identical
form in the fossil record
(Apart from organisms
such as certain types of
sharks, cockroaches or
ferns)
Evidence of Evolution
• Sequence also fits with ecology of the groups
– plants before animals, land plants before
land animals, plants suitable for insect
pollination before insects
• Many known sequences that link together
existing organisms with their ancestors
(Equus)
Evidence of Evolution:
Fossil Record
• Strong evidence that evolution HAS occurred
• Does not reveal mechanism for evolution
CLADOGRAM ACTIVITY
Adaptive Radiation
Textbook definition:
• Emergence of numerous species from a
common ancestor into an environment that
presents a diversity of new opportunities and
challenges
 Is this divergent or convergent evolution????
Homologous
• Similar due to inheritance
• Modified structure seen among different
groups of descendants
Homologous Structures:
Tetrapod Limb
• They are all built from many individual bones.
• They are all spin-offs of the same basic bone
layout: one long bone attached to two other
long bones.
Pentadactyl limbs
The difference?
• Homologous: look superficially different, serve
different purposes but structures are
anatomically similar b/c of shared
ancestry…not necessarily used the same
way…variations on a structural
theme…divergent evolution!)
Homology: Evidence for Evolution
• http://evolution.berkeley.edu/evolibrary/articl
e/similarity_hs_01
Analogous:
• serve the same function, but not constructed
similarly, no common ancestry (an example of
convergent evolution)
For these four critters, identify and
explain whether the structures are
homologous, analogous, or neither.
Importance of homology to
evolution
• Similar construction = evidence that
organisms in question have a common
ancestor…”unity of plan”
• Linked to embryological development as
well…
• Don’t prove anything – but difficult to explain
without evolution
• Presence of vestigial structures also linked –
traces of an organism’s evolutionary history
• Differing sizes and variations in morphology
• Basic shape and position of the limb bones =
same
• Suggests common ancestry
• **Not just limited to structures – also applies
to DNA!!! (molecular homologies)
• http://www.pbs.org/wgbh/evolution/educato
rs/teachstuds/unit3.html
Vestigial Structures
Florida Sand Skink
Vestigial Structures
• A structure of little or no importance to an
organism
• Historical remnants of structures that had
important functions in ancestors.
• Evolution MODIFIES existing structures.
Anatomical remodeling…
Embryological Development
• Compare early stages of development
• Reveals other homologies not seen in adult
forms
• Example: vertebrate tails
• Example: vertebrate pharyngeal pouches
Molecular Homologies
• All forms of life use the same genetic
machinery of DNA and RNA
• Genetic code is universal
• Organisms share many genes
• Many of the gene products (proteins) are the
same too
 Analysis of DNA and proteins: as number of
similarities increases, do does the degree of
relatedness.
Human, Chimpanzee, and Gorillas…who
is more closely related?
ACTIVITY