Which one of the following statements is accurate?
a. Natural selection works on variation
already present in a population.
b. Natural selection works on non-heritable traits.
c. Individuals evolve through natural selection.
d. Organisms evolve structures that they need.
e. None of the statements are true.
Speciation and Macroevolution
Website: http://evolution.berkeley.edu/
•
Describe the patterns found in the study of macroevolution.
•
Explain the concept of exaptation and describe an examples.
•
Explain why mass extinctions can be seen as times of great opportunity
•
Define the biological species concept. Explain its limitations when applied to all types
of living organisms.
•
Describe the different types of pre-zygotic and post-zygotic reproductive isolating
mechanisms.
•
Explain the process of allopatric speciation.
•
Explain what a cladogram or phylogenetic tree, what information does it provide and
how can it be constructed
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Are these two groups of flies
two populations of the same species
or
are they two different species?
What is a species?
- population or groups of populations
- members can potentially interbreed in nature
- AND produce fertile offspring
- appearance is not important
2
Fly scenario
• An event splits the original
population in two
• Generations later…
• An other event brings the groups
together
But they are not interbreeding!!!
• Speciation has occurred
• Speciation:
process by which new species
come into being
New species originate as modified
descendants of other species
Process of Speciation
Step 1: Genetic Isolation
gene flow between
two populations is interrupted
(populations become
genetically isolated from each other)
Step 2: Populations diverge genetically
genetic differences gradually accumulate
between the two populations
Step 3: Reproductive isolation
Some of these genetic differences
will be reproductive barriers
(traits that prevent two populations from interbreeding with each other)
3
Genetic differences  phenotype differences reproductive barriers
Reproductive barriers
before the zygote forms or after the zygote forms
What can cause speciation?
Geographical barrier
(Allopatric speciation)
4
Many geological and climatic events
can produce geographic barriers
causing speciation
Over the last 3. 8 billions of years
Microevolution
and
Speciation
has resulted on all the species that have ever existed
But only 1% are alive today because of…
If we reconstruct the speciation events
over this time….
5
Through descent with modification
over 3.8 billion years
all organisms are genetically related
Macroevolution:
evolution above species level
Reconstructing the speciation events
over the history of life
Trunk is one species over some time
Speciation happens and the tree splits
Continuing through time reveals new branching
6
How do scientists reconstruct these speciation events?
Systematists
are the detectives of life’s history
Evidence:
Observable characters
need to be derived (unique) and shared
Result:
Produce a tree-like diagram
Called phylogeny or cladogram
How to interpret a cladogram?
Who is more closely related to B?
A or C
If a new trait appears in green line, who A, B or C have it?
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Evolution is NOT a
climb up a ladder of progress
where organisms are always getting better
It is important to remember that:
Humans did not evolve from chimpanzees
Humans and chimpanzees
are evolutionary cousins and
share a recent common ancestor
that was neither chimpanzee nor human.
Humans are not "higher" or "more evolved"
than other living lineages.
Since our lineages split,
humans and chimpanzees
have each evolved traits
unique to their own lineages.
Importance of reconstructing evolutionary histories
We can observe large scale patterns
through out life’s history
We can organize species based on
their relationships
8
Macroevolution patterns
Stasis:
Some species don't change
much for a long time
Example
Coelacanth (discovered 1930)
Unchanged during the last 80 million years
Rapid change:
Macroevolution patterns
Extinction:
is the disappearance of
an entire species
from the face of the Earth
99% of species that have
existed are extinct today
Mass extinctions:
events that have
wiped out anywhere from
50% to 95% species
Adaptive Radiation :
event in which a group of species
rapidly diversifies
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Macroevolution Patterns
Convergent evolution:
Unrelated species develop similarities
due to adaptation to similar environments
Analogous characters
similar looking structures
due to adaptation to similar environments
not due to common ancestry
skeleton made of
cartilage
skeleton made
of bone
use gills to get
oxygen from the
water in which
they swim
go to the
surface and
breathe air in
through their
blowholes
don't nurse their
young
do nurse their
young
don't have hair
do have hair —
they are born
with hair around
their "noses"
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