Transcript Natural Selection and Genetics of Species

Evolution, Natural Selection &
Genetics of Species
History of Evolution
Darwin served as naturalist aboard the
H.M.S. Beagle on a British science
expedition around the world.
He observed variation in related or similar
species of plants and animals that were
geographically isolated from each other.
These observations were the basis
for his ideas.
Evolution
• Changes in a species over time
1. Species become different
2. Descendants differ from their ancestors
3. New species arise from existing ones
History of Evolution
Darwin presumed that populations of individuals changed
over time
• In 1844, he developed the concept of evolution
• Many years later that he published his idea
“I have called this principle, by which
each slight variation, if useful, is preserved, by the
term Natural Selection.”
- Charles Darwin, "The Origin of Species“
Speciation
• One species splits into two
locations (geographic isolation)
and over time becomes two
different species.
How Fast Does Evolution Occur?
• Gradualism
– Slow & steady change of one species into another
– Small changes continually build
• Punctuated Equilibrium
– Rapid periods of evolution
– Due to sudden environment change
– Ex: Mammal diversity after dinosaur extinction
Phylogentic Tree
• Signify a change in speciation
with regard to time
Speciation
• The formation of new species
• As new species evolve, populations become
reproductively isolated
– Reproductive Isolation
• Members of the same species cannot produce fertile offspring
(due to separation of population)
• Speciation in the Galapagos finches occurred by:
– Founding a new population
– Geographic isolation which led to reproductive isolation and
changes in the gene pool due to competition for food
Three Isolating Mechanisms
• Behavioral Isolation
– Capable of breeding but have differences in
courtship rituals
• Geographic Isolation
– Separated by geographic barriers like
rivers, mountains, bodies of water
• Temporal Isolation
– Two or more species reproduce at different
times
Donkey + Horse= Mule
• Mule is sterile, so a donkey and horse are
not the same species, since they don’t
produce viable offspring.
Tigon
Result of male tiger and female
lion mating inc aptivity.
Offspring are infertile.
Separated both geographically
and ecologically.
Liger
Result of male lion and female tiger
mating in captivity.
Offspring are infertile.
Four species of leopard frogs differ in their mating
calls. Hybrids are inviable.
These squirrels live on opposite sides of the Grand Canyon.
This is an example of geographic speciation.
Patterns in Evolution
• Extinction = the elimination of a species
• Extinctions occur continuously at a very low rate.
– Occur at roughly the same rate as speciation
– Usually affects a few species in a small area
– Caused by local changes in environment
Adaptive Radiation
• Small population of one species differentiates
into a variety of different species
FOUNDER SPECIES
Adaptation of Finch Beaks
Adaptations
Coevolution
• Two or more species evolve together in response
to changes in each other
Coevolution
• Can occur in beneficial relationships
– Both species receive benefits from the
other as a result of adaptations.
• Coevolution can occur in competitive relationships
– Sometimes called evolutionary arms race
Convergent Evolution
Describes evolution toward similar traits in
unrelated species
– Unrelated species with a similar environment
•
Faced similar evolutionary pressures
Divergent Evolution
Evolution toward different traits in closely
related species
– Cause = isolation
kit fox
red fox
ancestor
Different environments