Transcript Evidence for Evolution II

Review: Radiometric Dating
If Uranium-239 isotope has a half-life of 80 000
years, how many years would it take for all but
1/8 of the uranium to decay?
Second Half-life
First Half-life
100% Ur-239
½
Third Half-life
¼
1/8
80 000 yrs 80 000 yrs 80 000 yrs
= 240 000 years
It takes 240 000 years for Uranium-239 to decay
to 1/8 of its original amount (3 half-lives).
Evidence for Evolution II:
Biogeography,
Homologous, Analogous and
Vestigial Features
Biogeography
Biogeography: the scientific study of the
geographic distribution of organisms based on
both living species and fossils
Fossil Distribution
Remember Pangaea
–Fossils of the same species are found
on entirely different continents –
Africa, India, and Antarctica
Break up of
Pangaea
Fossil Distribution
• Mesosaurus – fossils found in both South
America and Africa
• Lived during the Permian, when Africa and
South America were joined
Current Distribution of Species
• Similar species are found on different continents
• Share a common ancestor that lived when the
continents were connected
• When the continents separated, the populations
were isolated and they diverged into different
species.
• Example: Different species of elephants are found in
Africa and India
Current Distribution of Species
Rhinos
Indian Rhino
African Lion
African Rhino
Old World Monkeys
(Africa/Asia)
Big Cats
Monkeys
New World Monkeys
(America’s)
American Puma
Indian Tiger
The Link with Biogeography
• All of these species share
common ancestors but
are found far from each
other today
• By looking at their
current distribution and
comparing it with the
fossil record, we can
establish both current
and ancient
biogeography
Example: Australian Marsupials
• Australia has the largest and most diverse
population of marsupials in the world
• Most other continents mostly have placental
mammals
• Why is this??
Australian Marsupials
• Marsupials evolved before placental mammals
• When placental mammals began outcompeting
marsupials on other continents Australia had already
separated and was isolated from them
• This allowed marsupials to diversify and evolve on
Australia without competition from placental
mammals
Homologous Features
“What can be more curious than the hand of a man, formed for
grasping, that of a mole for digging, the leg of a horse, the paddle
of a porpoise, and the wing of a bat, should all be constructed on
the same pattern, and should include the same bones, in the
same relative positions?”
-Darwin
Homologous Features
• A flipper or a wing has
no use for fingers, so
why should they have a
five-fingered structure?
• Why should giraffes
have the same number
of neck bones as
humans?
• If these features were
built from scratch, there
are more efficient ways
to do it
Homologous Features
• Homologous Feature: A structure with a
common evolutionary origin that may serve
different functions in modern species
Homologous Features in
Mammals
• In the forearms of different mammalian
species, the same features can be seen
Homologous Features in
Mammals
• We can use
homologous features
to “define” groups of
organisms
• In fact those hallmark
features of mammals
are also homologous:
– Live-birthed young
– Milk-producing
mammary glands
– Hair
All in the Family
• For species
to share a
homologous
feature,
they must
share a
common
ancestor
Examples of Homology
• Leaves and cactus spines
Examples of Homology
• Nest building behaviour
Examples of Homology
• Genes that Code for Eyes
Examples of Homology
• Embryos
Examples of Homology
• Embryos
Examples of Homology
• Embryos
Some Features go out of
Style
• Some homologous features indicate common
ancestry, but are no longer used
Analogous Features
• Analogous Feature: a structure that performs
the same function as another but is not
similar in origin or anatomical structure
Similarities in Unrelated
Species
• We observe similarities between unrelated
species
• Consider dolphins and sharks
Analogous Features
• We can expect to see analogous features
between species that fill similar ecological
niches
Examples of Analogous
Features
• Wings
Evolution of Flight or NearFlight
Examples of Analogous
Features
• Jointed Legs
Examples of Analogous
Features
• Beaks in squid and birds
Vestigial Features
• Vestigial Feature: A non-functioning, or only
marginally functioning, structure that is
homologous to a full functioning structure in
closely related species
Vestigial Features
• Vestigial features are homologous features
– They just aren’t used by that species any more
Examples of Vestigiality
• Dandelion Sex Organs
Examples of Vestigiality
• Hind Legs and Hips in Whales
Examples of Vestigiality
• Wings on Flightless Birds : Kakapo
Why do Features become
Vestigial?
• When a feature is not used, it is more likely to
become vestigial in time
• This can only happen if lack of use does not
hurt a population’s chance of survival
• Birds can only become flightless if they have
no need for wings
– In the case of the Kakapo, what might we guess
about predators?
Why do Features become
Vestigial?
• Birds can only
become flightless if
they have no need
for wings
– In the case of the
Kakapo, what might
we guess about
predators?
• No predators in New
Zealand
Assignment