Transcript Evolution and Darwin

HOW does Evolution
Occur?
Evolution
Evolution: The change of genetic information
over time, from one generation to the next.
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Ingredients for Evolution
“VIST”
Variation  mutations & sexual reproduction
Inheritance DNA passes on traits
Selection well matched or not to enviro
 choice of mates
• Time not a choice, can take millions of years
or happen relative quickly due to random
events
Mutations- achieve variation
Mutation: cause variation in genes
A change in the order of bases in DNA that
creates a new version of a gene (an allele)
5 Mechanisms of Evolutionary
Change:
1)
2)
3)
4)
5)
Mutation
Natural Selection
Gene Flow
Genetic Drift
Non-Random Mating
Natural Selection…
“Survival of the Fittest”
• Individuals with favorable traits:
( traits that are well suited for their environment)
 are more likely to survive & pass on their
genes via offspring
• Example:
English peppered moth (Biston betularia)
& the Industrial Revolution
- light and dark phases
Five Mechanisms of Evolution
(Review from last class)
1. Mutation:
Change in an organism’s DNA that
creates a new allele.
2. Natural selection:
Individuals well suited to their
environment are more likely to survive
Five Mechanisms of Evolution
3. Gene Flow:
The gain or loss of alleles (versions of a
specific gene) from a population by the
movement of individuals
– Immigration or emigration
4. Genetic drift:
The occurrence of a chance/random
event causes a particular version of a
gene (a trait) to become more OR less
common in a population
the relative frequency of a gene changes
due to chance!
Implies that inheritance of traits is NOT
ALWAYS related to fitness or natural
selection… sometimes CHANCE is a factor!
Examples of Genetic Drift:
1. Natural Disasters:
Earthquakes, Volcanoes, Floods
randomly wipe out part of the population
Eg) short legged goats at bottom survive goats at
top are killed, short leg gene gets passed on in a &
becomes much more
common!
2. Number of offspring
- an individual with a unique trait
(randomly) has more offspring than
it’s sister. The unique trait becomes
more common
Ex) Dog A has 10 puppies- curly hair
Dog B has 6 puppies- straight hair
 The allele for curly hair becomes
more common because Dog A had
more puppies not because it helps
survival!
• 3. Colonization:
-a small number of individuals are
separated and take over a new area
(eg. An island)
Ex) Darwin’s finches
Different islands have finches with
different beak types
could have resulted from BOTH
Genetic Drift AND Natural Selection
Speciation:
• The evolution of new species.
• Often results from reproductive isolation!
•  populations are separated & become so different
reproduction does not / cannot occur
Adaptive Radiation
• Introduction to new & diverse environments
creates new “selection pressure”…
– a new or different trait allows individuals to be
well suited to their new environment
– Over time this trait increases in frequency & can
lead to speciation
• Many different species come from one
common ancestor
• aka “Divergent Evolution”
• Example: Darwin’s Finches
Divergent Evolution in Darwin’s
Finches
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Divergent Evolution in Darwin’s
Finches
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Homologous Structures
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• Result from
adaptive
radiation
• Structures that
may LOOK
DIFFERENT &
SERVE
DIFFERENT
NEEDS BUT
originate from
the same body
parts
Analogous Structures
• Result from
convergent
evolution
• Structures similar
in appearance &
function BUT
have different
origins & internal
structure
Convergent Evolution
• Species from different evolutionary branches
come to resemble one another if they live in very
similar environments.
• Example:
1. Ostrich (Africa) and Emu (Australia).
2. Sidewinder Snake (Mojave Desert) and
Horned Viper (Middle East Desert)
Two Theories of How New
Species Arise
1. Gradualist Model (Darwinian):
Slow changes in species over time.
2. Punctuated Equilibrium:
Evolution occurs in spurts of relatively
rapid change.
A
B
Review from last class…
How do New Species Arise?
1. Gradualist Model (Darwinian):
Slow changes in species over time.
2. Punctuated Equilibrium:
Evolution occurs in spurts of relatively
rapid change.
Five Mechanisms of Evolution
5.Non-random mating:
The selection of mates other than
by chance.
• “Sexual Selection”
• Video to illustrate
• (8mins)
Does Sex Matter?
• Yes!
• Evolution can be driven by mate choice
and pressure to attract mates
• Mating is NOT random…it creates a
“selection pressure”
• Sex = “an evolutionary arms race”
5. Non-random mating:
The selection of mates other than by chance.
• Video: “Why Sex?”
(~8 mins)
Results of Sexual Selection
• Males: competition
• Males are often selected for increased size for fighting
other males, defending territory etc in order to obtain
access to females
• Females: choice of mates
• “Handicap Principle”- females are attracted to males
with potentially damaging traits (ie bright colours)
because it advertises “good genes” ie) ability to be
colourful and still avoid predators