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Chapter 29
The Problem
 Evidence for evolution came from the finding of fossils
showing that there were animals that use to exist that
no longer do.
 What caused older species to die out and new ones to
come into existence?
Evidence: Ancient Giraffes
 Fact: The ancestors of modern-day giraffes had much
shorter necks.
 How and why did this happen?
Lamarck’s Theory of Evolution:
The Theory of Inheritance of
Acquired Characteristics
 Jean Baptise de Lamarck suggested the following theory:
The more an animal uses a particular part of its body, the
stronger and more developed it becomes.
2. These characteristics would then be passed on to its
offspring. This process repeated over generations would
cause a species to change dramatically.
1.
For example, low-lying food became scarce and the giraffes
needed to reach high in the air to get food off of trees.
This caused their necks to lengthen. They then gave birth
to offspring with longer necks.
Lamarck
 According to Lamarck, individual organisms evolve
and have evolved children.
Problem #1
 Scientists conducted the following experiment:
 They cut off the tails of mice and then allowed
them to reproduce.
 Their offspring had normal-length tails.
 This was repeated for 22 generations, with the
tail-length remaining the same.
 Why is this a problem?
According to Lamarck, since the mice
did not use their tails throughout
their lives, their offspring should have
shorter, less developed tails. Yet, they
Problem #2
 In addition, the modern theory of genetics states that
an organism passes its gametes to its offspring.
 There is no evidence that the events of one’s life have
any impact on the genetic makeup of one’s gametes
(other than non-disjunction in meiosis, mutagens,
etc).
Darwin’s Theory of Evolution:
Natural Selection
 Evolution is the process of species of animals
changing throughout time.
 Note: Single animals do not evolve. Entire species
evolve.
Darwin’s Theory of Evolution
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2.
3.
4.
5.
6.
Overpopulation - All species produce more children than can
actually survive.
Competition- Since food is limited, all offspring cannot
survive.
Variation – Members of a species have minor genetic
differences that can be helpful, unhelpful or neutral.
Adaptation- Some of those genetic variations will improve the
individual’s likelihood of survival and reproducing (passing on
genetics).
Natural selection- The individuals with the best variations
will have more offspring. In the next generation, there will be
more individuals with this characteristic.
Speciation- Over MANY generations, enough of these
variations will accumulate and the unfavorable variety will
disappear and be totally replaced by the favorable variety.
Applying Darwin’s Theory -Giraffes
1.
2.
3.
4.
5.
6.
Overpopulation - Too many giraffes
Competition- Not all the giraffes can survive
Variation – Some have differences. Longer necks,
shorter necks, bigger tail, shorter tail, etc.
Adaptation- Longer necks are useful
Natural selection- Those with the longest necks
survive best.
Speciation- Over MANY generations, only giraffes
with long necks exist.
Population Genetics
 In terms of genetics, Darwin’s evolution simply means
that a certain allele becomes more common in a
population’s gene pool.
 “Gene pool” means that total of all alleles present in a
population.
 Example with giraffes (R = short neck and r = long
neck), then in Generation 1 the population is 99% R
and 1% r. By the next generation, it might be 98% R
and 2% r, etc.
What
can
create
these
variations?
 Mutations – Sometimes,
random mutations can result in
new alleles. The overwhelming
majority of the time, they are
detrimental. Sometimes, they
are awesome.
 Genetic RecombinationSometimes, a new combination
is what adds to an advantage for
an individual.
Types of Adaptations: Camouflage
 Camouflage is when an organism blends into its
surroundings to avoid detection.
Types of Adaptations:
Warning Coloration
 Serves to warn other animals not to eat it because it is
poisonous.
Types of Adaptations:
Mimicry
 The Viceroy butterfly evolved to appear like the
Monarch even though it is not poisonous. Clearly it
evolved after the Monarch.
Types of Adaptations:
Conservation of Energy
 Certain humans developed adaptations to conserve
energy. This is very useful in times of famine, scarcity.
In times of plenty, this can be a disadvantageoverweight.
Israel Kamakawiwo'ole
Directional Selection
 Directional Selection – In this case, the most
extreme of the variation is the most beneficial for
the organism.
 Therefore, the majority of the species will move in that
direction.
 Example: Giraffes’ neck length- taller is better.
# of
organisms
alive
Neck length
Stabilizing Selection
 In Stabilizing Selection,
the extremes are
unfavorable for the
organisms and the
percentage of the
population in the middle
will increase.
 Example: Mice in winter.
Mice that are too small are
not strong enough to
burrow underground and
mice that are too large use
up too much energy in
winter. Mice of medium size
have the best advantage.
Number of
organims
alive
Size of mouse
Disruptive Selection
 Example: Crabs range in
color from white to dark
brown. If their environment
includes both sandy
beaches and dark mud, then
both extremes will survive
better and the middle ones
(light brown) will be less
likely to survive.
 This will eventually result in
two populations – one of
white and one of dark
brown.
 At some point, they will
become so different that
they will be considered
different species.
Number of
organisms
alive
Darkness of color
Speciation
 When do we consider something a different species?
 Speciation is complete when the new individuals
cannot reproduce with members of the original
group.
 How does this occur?
 Through geographic isolation, a certain population of
a species becomes separated from a different
population. Each population breeds among only itself
for an extended period of time. After enough time, the
two species are no longer able to interbreed.
Can they reproduce together?
Are they the same species?
1.
Labrador
and
Golden Retriever
Yes
Canis lupus familiaris
Canis lupus familiaris
Canis lupus familiaris
Squirrel and Mouse
Sciurus carolinensis
Mus musculus
XXXXX
Horse and Donkey
Equus asinus
Equus caballus
Mule
Equus Caballus x Equus Asinus
In fact, to be
considered the
same species,
two organims
must be able to
have offspring
that can have
its own
offspring,
unlike the
mule.
Evolution and Modernity:
Industrialization and Pollution
 For a very long time, Earth appeared very
similar and evolution was a very gradual
process.
 Modernity/Industrialization has changed
(and in some cases, sped up) that process.
 Example:
 The increase of air pollution in England
gave the darker variety of peppered moth
an advantage, while in the nonindustrialized areas of England, the light
variety continued to dominate.
Evolution and Modernity:
Bacteria and Antibiotic
 Another advance in recent years is the development of
antibiotics. These drugs are very effective at killing
harmful bacteria and have saved billions of human
lives in the past 100 years.
 However, as antiobiotic use continues, it becomes less
effective because the bacteria evolves very rapidly.
Evolution and Modernity:
Bacteria and Antibiotic
 Example: Penicillin. A person becomes infected with bacteria.
The bacteria is living in a person’s intestines, feeding off waste
products. Many different types of bacteria are present. There are
1 million harmful bacteria present. The person is treated with
Penicillin, an antibiotic. The Penicillin kills all the bacteria,
except 100. However, these bacteria continue to survive, and have
no competition from other bacteria for food. They expand and
now there are 1 million bacteria that are resistant to Penicillin.
Oops. This is how bacteria develop resistance to antibiotic.
Bacteria and Antibiotic
 So, how does antibiotic work?
1. It might kill all the bacteria
2. It might reduce the number so the body can defeat the
3.

invader
Sometimes it doesn’t work and a different antibiotic
needs to be used. Researchers are constantly developing
new antibiotics as the ones we have rapidly become
useless.
[This is why antibiotics should be used as infrequently as
possible and why you cannot stop in the middle of a
course of antibiotic.]
Understanding Human Evolution
From primitive life to life today:
www.youtube.com/watch?v=dYphAH2tKYE&feature
=related
2. From apes to humans:
http://www.youtube.com/watch?v=q2ZE2NGvJ0I&fe
ature=related
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