Natural Selection in
Action
Section 6.3
Discussion
• During the past
several hundred
years, a rapidly
expanding human
population has
caused some species to become extinct either
from habitat destruction or overhunting.
• If people are as much a part of the environment
as trees and birds are, are people’s actions just
parts of natural processes?
media-2.web.britannica.com
Changes in Population
• Well adapted organisms are more
likely to survive and reproduce.
• Example: Before the Industrial
Revolution, the peppered moth was
mostly found in a light-grey form with
little black speckled spots. These
moths were able to blend in with the
light-colored lichens and tree bark,
and the less common black moth was
more likely to be eaten by birds.
en.wikipedia.org
Changes in Population
• Due to widespread pollution
during the Industrial Revolution,
many of the light-colored
lichens died out, and the
trees they rested on became
blackened by soot, causing
most of the light-colored
moths to die off from predation.
However, the dark-colored moths
flourished because of their ability
to hide on the darkened trees.
en.wikipedia.org
en.wikipedia.org
Changes in Population
• Since then, with improved
environmental standards,
light-colored peppered
moths have again become
common.
• This evolved darkening of
color due to industrialization
is called melanism.
RealPlayer Videos\Evolution of the Peppered
Moth - Bing Videos.flv
en.wikipedia.org
en.wikipedia.org
Changes in Population
• Something similar has occurred in
the elephant population in
Uganda, since most elephants in
that region have tusks, which are
very valuable.
• In 1930, 99% of the male elephants had tusks
(1% tuskless). Due to hunting, today around 15%
of the male elephants are tuskless. Why?
• Tuskless elephants are relatively safe and live to
reproduce, unlike their brothers with tusks.
www.wildlife-pictures-online.com
Insecticides
• When insecticides are used, most of
the insects are killed. Those that
survive are resistant to the chemical.
They live to reproduce, and the
insecticide doesn’t work as well on
future generations – most offspring
inherited the trait of being insecticide
resistant.
• Evolution takes time, but insects have
a short generation time, so they can
evolve more quickly than other
species.
www.drearth.com
Insecticides
Bacteria and Antibiotics
• Something similar can occur
when a bacterial infection is
treated with antibiotics.
• Some bacteria are less
susceptible to the affects of the
antibiotic. They may not be
killed by it or may take longer
periods of exposure for the
antibiotic to work.
www.faqs.org
www.steadyhealth.com
Bacteria and Antibiotics
• This is why you should
always take all of your
prescription, even once you
get to feeling better.
Otherwise, the resistant
bacteria will live and
reproduce and you will get
sick again.
• Further treatment will be
less effective, since more of
the bacteria are resistant.
www.aenvirocure.com
Adaptive Coloration
• Penguins, puffins, killer
whales and blue sharks are just
some of the ocean animals that
have white bellies and black or
dark blue dorsal surfaces. This
type of coloration is called
countershading.
naturescrusaders.files.wordpress.com
www.esr.org
www.cs.usask.ca
www.free-desktop-backgrounds.net
Adaptive Coloration
• When seen from below, the white underside
helps the animal blend into the lighter sky
above the water.
• Viewed from above,
the dark coloration
makes the animals
difficult to see
against the ocean
depths.
www.doobybrain.com
Sexual Selection
• The selection of traits that is
brought about by a specific
pattern of mating.
• In many organisms, members of
one sex must compete with each
other for access to mates.
• The “choosiness” of one sex may
drive the evolution of traits that
confer no apparent advantage to
the opposite sex.
www.bio.davidson.edu
img1.photographersdirect.com
Sexual Selection
• Females prefer to mate with
colorful males, so colorful males
have more offspring than
noncolorful males. Colorful males
are more likely to pass on their
genes to the next generation,
increasing the proportion of
colorful males.
• The long tails and colorful plumage
of many male birds are considered
examples of such “runaway sexual
selection.”
RealPlayer Videos\Sexual Selection and the Art of Courtship.flv
img.xcitefun.net
s3.amazonaws.com
Forming a New Species
• New species can form if a group gets cut off
from the rest of the population.
• The new population adapts to its
environment over generations, and
eventually the new population is different
enough from the old population that they
can no longer interbreed, even if brought
back together.
Forming a New Species
• Some species that have adapted to
live in total darkness no longer even
have eyes. Just as whales have
evolved into legless forms, these
species have completely adapted to
life without light, and have evolved
forms lacking eyes altogether.
• Examples include blind cave fish,
eels, salamanders, worms, shrimp,
crayfish, spiders, beetles and
crickets.
webecoist.com
forum.globaltimes.cn
webecoist.com
Forming a New Species
• The leopard frog and the
pickerel frog are similar
species and probably had
the same ancestor species.
• After separation, they
began to mate at slightly
different times of the year,
so they can no longer
interbreed.
www.torontozoo.com
Forming a New Species
• This process is called speciation and involves 3
basic steps.
• Separation – part of a population becomes
separated from the rest (possibly by new water or
land formations)
• Adaptation – natural selection will act on the
separate populations in different ways, depending
upon their environmental conditions.
• Division – the two groups grow to be distinct from
one another and can no longer interbreed – they
have become different species.
RealPlayer Videos\Speciation.flv
Speciation Example
Speciation Example
Speciation Example
RealPlayer Videos\A look at the finches of the Galapagos islands.flv
Watch the PBS video on Evolution:
http://video.pbs.org/video/1372073556/
Nova Video: What Darwin Never Knew
A video in 8 15-min parts
RealPlayer Videos\What Darwin Never Knew Part 1 8 NOVA
HD.flv
RealPlayer Videos\What Darwin Never Knew Part 2 8 NOVA
HD.flv
RealPlayer Videos\What Darwin Never Knew Part 3 8 NOVA
HD.flv
RealPlayer Videos\What Darwin Never Knew Part 4 8 NOVA
HD.flv
Nova Video: What Darwin Never Knew
A video in 8 15-min parts
RealPlayer Videos\What Darwin Never Knew Part 5 8 NOVA
HD.flv
RealPlayer Videos\What Darwin Never Knew Part 6 8 NOVA
HD.flv
RealPlayer Videos\What Darwin Never Knew Part 7 8 NOVA
HD.flv
RealPlayer Videos\What Darwin Never Knew Part 8 8 NOVA
HD.flv
Or watch the PBS video on Evolution (streamed video):
http://video.pbs.org/video/1372073556/
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http://www.bio.davidson.edu/people/vecase/Behavior/Spring2009/Hartye/Media/Male_and_female_superb_fairy_wren.jp
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http://img.xcitefun.net/users/2009/08/107429,xcitefun-pet-birds-1.jpg
http://s3.amazonaws.com/readers/scienceray/2008/07/27/238861_10.jpg
http://www.torontozoo.com/adoptapond/guide_images/Leopard%20Frog.jpg
http://www.torontozoo.com/adoptapond/guide_images/Pickerel%20Frog.jpg
http://forum.globaltimes.cn/forum/attachment.php?attachmentid=37650&thumb=1&d=1283844936
http://webecoist.com/wp-content/uploads/2010/08/Eyeless_2.jpg