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Evolution
AP Biology
Essential Questions
 What
is evolution?
 How does evolution work?
 What is the mechanism of evolution?
 How
does natural selection work?
 What are the different variations of selection?
 What
is the evidence for evolution?
History of Evolutionary Theory
 Linnaeus
 Developed
a system of
classification based on body
structures (morphology)
 Lamarck
 Said
species could “will”
themselves to change
Images taken without permission from http://65.107.211.206/victorian/science/lamarck.jpg
and http://www.necsi.org/projects/evolution/lamarck/lamarck/giraffes.jpg
History of Evolutionary Theory
 Darwin
 Natural
Selection causes species
to change
 Mendel
– now used as another
way to look at evolution
 Genetics
Img Src: http://www.panspermia.org/darwin.jpg
Natural Selection
5 parts:
1. Population growth has the
ability to be exponential.
2. Populations tend to be stable
in size (despite #1).
3. Resources are limited.
4. Individuals vary in phenotype.
5. Much phenotypic variation is
heritable.
Img Src: http://www.abc.net.au/nature/parer/img/galapagos.gif
Natural Selection (in summary)
 There
are more individuals produced than
the environment can support  leads to
competition for resources.
 Individuals with advantageous traits in this
competition will survive to reproduce and
pass on those advantageous traits to the next
generation.
Artificial Selection
 Breeding
animals or plants to have the
desired traits
 Ex. Dog & Cat breeds
Great Dane
Shar-Pei
American curl cat
Images taken without permission from http://www.caine.de.rasa.ham.8m.com/images/shar_pei.jpg,
http://www.petsmart.com/aspca/images/dogs/great_dane.jpg, http://www.cfainc.org/breeds/profiles/articles/acurl.html
Newer developments in Artificial Selection
 Cocker
spaniel + poodle
= Cockapoo
 Labrador + Poodle =
Labradoodle
 Why mix with poodles?
 Their
fur tends to shed
less– they were originally
bred in an effort to create
a guide dog for people
who were allergic to dogs.
Vestigial Structures

Structures that are no
longer used in an
organism


Ex. Appendix, tail
bone
Many structures
present in embryos are
also used to show
common ancestry -developmental biology
Img Src: http://www.vh.org/adult/provider/anatomy/AnatomicVariants/SkeletalSystem/Images/19.html
Analogous Structures
 Similar
functions, different structures
 Indicates different ancestors
 Ex. Bird wing, butterfly wing
 Result from convergent evolution:
similar selection pressures cause similar
structures to evolve.
Homologous structures
 Similar
structure,
different functions
 Indicate a common
ancestor
 Ex. Human hand,
seal flipper, bat
wing
Biogeography
Study of distribution of
organisms (past and present)
 Demonstrate that organisms can
evolve similarly to one another in
similar environments from
different ancestors
 Ex. Marsupials in Australia –
they are only found in Australia
but some share similar
characteristics with other
organisms

Genetic Drift
 Changes
in the gene pool caused by
random events
 Examples: Bottleneck Effect, Founder
Effect, Geographic Isolation
Bottleneck Effect

drastic reduction in population (due to natural
disasters, predators, etc.)
Example of Bottleneck Effect:
Cheetahs
Img Src: http://www.meerkats.com/images/cheetah-cub.jpg
Img Src: http://easyweb.easynet.co.uk/~iany/patterns/images/cheetah.jpg
Founder Effect
 A few
individuals become isolated from the
original population
 The resulting population is not
representative of the original population
Example of
Founder Effect
Another Example of Founder Effect: Ellis-van Creveld Syndrome
Img src: http://www.emedicine.com/ped/images/296682EVC-polydactylya.jpg
Img Src: http://www.emedicine.com/ped/topic660.htm
Geographic Isolation
 When
physical
separation/isolation results in
the formation of new species
 Is a cause of founder effect
 Adaptive radiation = many
species evolving from one
original ancestor
Example of Geographic Isolation
Img Src: http://www.desertfishes.org/na/cyprinod/cyprinod/cssalinu/cssalin1.jpg
Gene Flow
 Migration (immigration, emigration)
 Breeding across prior barriers (cultural barriers, for
instance, as in human populations)
 Changes allelic frequencies
 Ex. Human migration
Phenotypic Polymorphism
 Defined
 Due
-
as variety of physical traits
to
genetic variation
genetic polymorphism
nonheritable variation
Fitness
 fitness = contribution of individual to gene
pool, relative to others’ contributions
 relative fitness = contribution of a genotype
(all individuals alike)
 fitness of 1 means you (or your genotype)
contribute at a maximum (100%)
 fitness of 0 means you (or your genotype)
do not reproduce at all
Types of Selection
 Selection
= Environment chooses those with
the best adaptations to survive
Stabilizing Selection = middle phenotype is selected for
Disruptive Selection
 The
two extremes are selected for
 Ex. Snails
Directional Selection = one phenotype is selected for
Img Src: http://web.nmsu.edu/~wboeckle/pepper_moth2.JPG
Industrial melanism
Heterozygote Advantage
 When
being heterozygous
gives you an advantage
 Explains why a harmful
recessive allele does not
get eliminated from a
population
 Ex. Sickle cell anemia –
heterozygotes are resistant
to malaria
Img Src: http://www.nidcd.nih.gov/news/releases/02/malaria.jpg
Img Src: http://www.unomaha.edu/~swick/images/sickel.jpg
Sexual Selection
 Genders
appear different
due to Sexual
Dimorphism
 Competition is inter- and
intragender specific
 Ultimately has to do with
competition for higher
fitness
Constraints on Natural Selection
 Populations
are not perfectly suited to their
environments because
 Environments
constantly change (Ex. A new
population of people marooned from a breaking
ship begin a new population. They do not
necessarily represent the best of the gene pool)
Constraints on Natural Selection
 Populations
are not perfectly suited to their
environments because
 Evolution
is slow and new structures rarely
form (Ex. Birds have 2 wings rather than 4,
which could help with flight, because they
evolved from a 4-appendage reptile; 2 wings
and 2 legs)
Constraints on Natural Selection
 Populations
are not perfectly suited to their
environments because
 Adaptations
are compromised (Ex. seal legs would help
in land motion, but swimming with legs is less efficient
than with flippers)
Constraints on Natural Selection
 Populations
are not perfectly suited to their
environments because
 Natural
selection can only pick the best
variation—it can’t create variations