Evolution
Part 1
BIOL 1407
Evolution
• Heritable genetic change in populations
or groups of populations over time
• Changes in gene pool
Evolution
• Also includes populations diverging
from one another over time
 may lead to new species
Mechanisms of Evolution
• Genetic Drift
– Population Bottlenecks
– Founder Effect
• Gene Flow
– Immigration
– Emigration
• Mutations
• Natural Selection
Genetic Drift
• Changes in gene pool of populations
due to random chance
Genetic Drift
Genetic Drift
Image Credit: UC Museum of Paleontology's Understanding Evolution www.evolution.berkeley.edu
Genetic Drift
• Genetic drift has a bigger effect on
small populations.
Bottleneck Effect
• Changes in gene pool of populations
due to some event
 drastically reduces population
Bottleneck Effect
• Survival is random
• Whether an organism survives does not
depend on any characteristic (allele)
Example of Bottleneck Effect
• Population of plants on
a mountain side
• An avalanche wipes
out all but a patch of
plants behind the
shelter of a large
outcrop.
Example of Bottleneck Effect
• Plants behind the outcrop survived only
because they were out of the path of the
avalanche.
• There was nothing about the plants’
genes that influenced survival.
Example of Bottleneck Effect
• Surviving population has an allele
frequency different from the original
population.
Bottleneck Effect
Bottleneck Effect: Cheetahs
• 10,000 years ago,
cheetah
populations
worldwide
crashed
• Due to climate
change
•
Photo Credit: Courtesy of Smithsonian National
Zoo @ nationalzoo.si.edu
Cheetahs
• Only cheetahs
in Africa &
Eurasia
survived
• Location, not
genes 
Survival
•
Photo Credit: Kevin Walsh, 2006,
Wikimedia Commons
Cheetahs
• Cheetahs today: Genetically identical
•
Photo Credit: Lukas Kaffer, 2007, courtesy of Wikimedia Commons
Bottleneck Effect:
Northern Elephant Seals
• Once numerous in
the northern Pacific.
• 1800s: Hunted
extensively for
blubber
•
Photo Credit: Michael Baird of bairdphotos.com,
courtesy of Wikimedia Commons
Northern Elephant Seals
• Only 100-1000
animals in a
Mexican colony
survived
•
Photo Credit: Michael Baird of bairdphotos.com,
courtesy of Wikimedia Commons
Northern Elephant Seals
• Today:
>100,000
individuals
• Very little
genetic
diversity
•
Photo Credit: Mila Zinkova, 2008,
courtesy of Wikimedia Commons
Founder Effect
• New population established by very
small number of individuals (“founders”)
• By chance, founder group has a
different allele mix than original
population
Example of Founder Effect
• 200 German
immigrants
founded the
Old Order
Amish of
Pennsylvania
•
Photo credit: : Matthew Trump, 2004,
Wikimedia Commons
Old Order Amish
• One couple
brought allele
polydactyly
 Six fingers
and toes
•
Photo credit: G. Baujat and M
LeMerrer, 2007, Wikimedia
Commons
Old Order Amish
• Inbreeding has 
frequency of
polydactyly
• Click on this link:
http://www.pbs.org/wgbh/evolution/library/
06/3/l_063_03.html
•
Photo credit: gadjoboy, 2006, Wikimedia
Commons
Gene Flow
• Movement of alleles between populations
• Immigration: movement of alleles into a
population
• Emigration: movement of alleles out of
population
Example of Gene Flow
• Transfer of pollen from
one population of
sunflowers into another
population of
sunflowers
•
Photo Credit: Sunflower Pollen, Courtesy of
Wikimedia Commons
Example of Gene Flow
• Male juvenile Belding’s
ground squirrels
emigrate from their
birthing population to
new populations.
• 40-70% emigrate as
juveniles. Remaining
males leave by the end
of their first year.
•
Photo Credit: Courtesy of Yathin at FlickR,
http://www.flickr.com/photos/yathin/807378578/i
n/set-72157600812861150/
Mutations
• Mutations can
add new alleles
to a population
• Review this BIOL
1406 concept
•
•
Photo Credit for black Eastern Fox Squirrel: Jeffrey
Pippen, Duke University
Photo Credit for wild-type Eastern Fox Squirrel:
Calibas, 2007, Wikimedia Commons
Asexual Populations
• Mutations are
primary source
of genetic
variation in
asexual
populations
•
Photo Credit for E. coli 0157 colonies: Centers
for Disease Control, 2005, Wikimedia
Commons
Natural Selection
• Environment determines which genes
are passed onto the next generation
• Based on which individuals successfully
survive and reproduce
Natural Selection
• Requires:
– Genetic Variation
– Overproduction of Offspring
– Struggle for Existence
– Differential Survival and Reproduction
View video at: http://www.pbs.org/wgbh/evolution/library/11/2/e_s_4.html
Photo credit: Dean E. Briggins, U.S. Fish and Wildlife Service, http://www.nsf.gov/news/news_images.jsp?cntn_id=104263&org=LPA
Genetic Variation
• Organisms in the population vary in their
characteristics
• Variations are heritable  Passed from
parents to offspring
Variation in Snail Shells
Flower
Variations
Natural
Selection
Flow
Chart
How
Natural
Selection
Works
View “Pocket Mouse and Predation” at
http://www.hhmi.org/biointeractive/evolution/animations.html
Photo Credit: Cheryl S. Brehme, USGS at http://soundwaves.usgs.gov/2006/02/pubs.html
View “Pocket Mouse Evolution” at
http://www.hhmi.org/biointeractive/evolution/animations.html
Photo Credit: J. Harris, American Society of Mammalogy, at: http://www.mammalogy.org/mil_images/images/mid/752.jpgl
Artificial Selection
• Humans select which genes are passed
onto the next generation
• Based on characteristics that humans
find valuable or desirable
View “Dog Breeding” at http://www.hhmi.org/biointeractive/evolution/video.html
Photo credit: papillon.cz, courtesy of Wikimedia Commons (http://commons.wikimedia.org/wiki/Image:%21flowers.jpg)
View “Breeding Teosinte” at http://www.hhmi.org/biointeractive/evolution/video.html
Photo credit: USDA, 2005, courtesy of Wikimedia Commons
Another Example of Artificial Selection
Sexual Selection
• Some
characteristics
influence
individual’s
chance of
mating
•
Photo Credit: Ian Sewell, 2006,
Wikimedia Commons
Sexual Selection
• Individual may
have shorter life
but will have
better chances
of mating and
producing
offspring
•
Photo Credit: David Dennis, 2007,
Wikimedia Commons
Types of Sexual Selection
• Mate Competition
– One sex competes for access to the other
sex
– Other sex always “chooses” winner
• Mate Choice
– One sex chooses mate based on
characteristics of other sex
Example of Mate Competition
• Male bighorn
sheep fight for
mates
• Male with largest
horns usually
wins
•
Photo Credit: Alan D. Wilson,
naturespicsonline.com,
courtesy of Wikimedia
Commons
Video of Bighorn Sheep Fighting:
http://www.youtube.com/watch?v=WKmGiSm3-2U
Photo Credit: Jon Sullivan, Wikimedia Commons
Example of Mate Choice
• Peacocks
display their tails
• Females choose
male with
showiest tail
•
Photo credit: Aaron Logan,
www.lightmatter.net, courtesy of Wikimedia
Commons
Example of Mate Choice
• Large tails
decrease
survival of
peacocks
• Natural selection
favors small tails
•
Photo credit: Jörg Hempel, courtesy of
Wikimedia Commons
Example of Mate Choice
• Peacocks with
small tails do
not mate
• Mate choice
favors large
tails
•
Photo credit: Jyshah, 2007, courtesy
of Wikimedia Commons
View the video at:
http://www.pbs.org/wgbh/evolution/library/01/6/l_016_09.html
Photo credit: Myukii, courtesy of Wikimedia Commons
The End
Unless otherwise specified, all images in this presentation came from:
Campbell, et al. 2008. Biology, 8th ed. Pearson Benjamin Cummings.