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5.2 Natural selection
The image shows the changes
of beak shape in the Galapagos
finch to suit the different food
sources available on different
islands in the archipelago.
Natural selection has caused
one species to evolve into
different, distinct species.
adapted from: http://online.itp.ucsb.edu/plecture/nurse/oh/27.jpg
5.2
• Essential idea: The diversity of life has evolved
and continues to evolve by natural selection.
History of Evolutionary Thoughts
Lamarck’s Theory of Evolution
Jean-Baptiste Lamarck, 1809
one of first scientists to
understand that change occurs
over time
stated that changes are
adaptations to environment
acquired in an organism’s lifetime
said acquired changes were passed
to offspring
Lamarck’s Theory of Evolution
Idea called Law of
Use and Disuse
If a body part were
used, it got
stronger
If body part NOT
used, it
deteriorated
Lamarck’s Theory of Evolution
Inheritance of Acquired Characteristics
proposed that by selective use or disuse of
organs, organisms acquired or lost certain traits
during their lifetime
these traits could then be passed on to their
offspring
over time this led to new species
Lamarck’s Theory of
Evolution
Lamarck’s Mistakes
 Lamarck did not know how traits were inherited
(Traits are passed through genes !)
 genes are NOT changed by activities in life
 change through mutation occurs before an
organism is born
Charles Darwin
 1809-1882
 British naturalist
 In 1858, Darwin and
Wallace independently
proposed the idea of
evolution by natural
selection
If they both had the idea, then
why is only Darwin really
remembered???
Charles Darwin
 Darwin published On the Origin of Species by Means of
Natural Selection the following year
Charles Darwin (1809-1882)
For more information on his life go to:
http://www.aboutdarwin.com/timeline/time_01.html
Archaeopteryx is one of the most important
fossils ever found. Thought to be a
transitional form between birds and reptiles.
http://www.ucmp.berkeley.edu/diapsids/birds/
archaeopteryx.html
5.2.U1 Natural selection can only occur if there is variation among members of the same species.
The harlequin ladybird
(Harmonia axyridis) is
highly variable in
appearance, with over
100 different color forms
reported worldwide.
The implication of
variation is that some
individuals will be more
suited to particular
conditions and hence
more likely to survive.
http://www.arkive.org/harlequin-ladybird/harmonia-axyridis/image-G77560.html
5.2.U1 Natural selection can only occur if there is variation among members of the same species.
• Natural selection favors traits that help an organism to survive
• If all organisms are identical, then they all have the same chances
of surviving and reproducing and therefore natural selection
cannot happen
• So why is variation important?
- Genetic variation in a population allows some individuals to survive should
the environment change
- We have learned the importance of genetic variation in our crops from
history: Irish Potato Famine
http://evolution.berkeley
.edu/evolibrary/article/a
griculture_02
5.2.U2 Mutation, meiosis and sexual reproduction cause variation between individuals in a species.
5.2.U2 Mutation, meiosis and sexual reproduction cause variation between individuals in a species.
5.2.U2 Mutation, meiosis and sexual reproduction cause variation between individuals in a species.
5.2.U2 Mutation, meiosis and sexual reproduction cause variation between individuals in a species.
5.2.U2 Mutation, meiosis and sexual reproduction cause variation between individuals in a species.
5.2.U2 Mutation, meiosis and sexual reproduction cause variation between individuals in a species.
5.2.U2 Mutation, meiosis and sexual reproduction cause variation between individuals in a species.
5.2.U2 Mutation, meiosis and sexual reproduction cause variation between individuals in a species.
5.2.U2 Mutation, meiosis and sexual reproduction cause variation between individuals in a species.
5.2.U3 Adaptations are characteristics that make an individual suited to its environment and way of life.
5.2.U4 Species tend to produce more offspring than the environment can support.
Why don’t they all survive???
http://i.guim.co.uk/static/w-620/h--/q-95/sysimages/Guardian/Weather/WeatherWatch/2013/3/29/1364579451698/Female-Frog-and-Frogspawn-008.jpg
5.2.U5 Individuals that are better adapted tend to survive and produce more offspring while the less
well adapted tend to die or produce fewer offspring.
5.2.U5 Individuals that are better adapted tend to survive and produce more offspring while the less
well adapted tend to die or produce fewer offspring.
5.2.U5 Individuals that are better adapted tend to survive and produce more offspring while the less
well adapted tend to die or produce fewer offspring.
5.2.U5 Individuals that are better adapted tend to survive and produce more offspring while the less
well adapted tend to die or produce fewer offspring.
5.2.U5 Individuals that are better adapted tend to survive and produce more offspring while the less
well adapted tend to die or produce fewer offspring.
5.2.U5 Individuals that are better adapted tend to survive and produce more offspring while the less
well adapted tend to die or produce fewer offspring.
5.2.U5 Individuals that are better adapted tend to survive and produce more offspring while the less
well adapted tend to die or produce fewer offspring.
5.2.U6 Individuals that reproduce pass on characteristics to their offspring.
Allele frequency
changes
Gene frequency = the number of times an allele appears in a gene pool compared to other alleles
5.2.U6 Individuals that reproduce pass on characteristics to their offspring.
Allele frequency
changes
Gene frequency = the number of times an allele appears in a gene pool compared to other alleles
5.2.U7 Natural selection increases the frequency of characteristics that make individuals better adapted and
decreases the frequency of other characteristics leading to changes within the species.
Allele frequency
changes
Gene frequency = the number of times an allele appears in a gene pool compared to other alleles
Summary: Darwin’s Theory of Natural Selection
1. Populations produce more offspring than can possibly
2.
3.
4.
5.
survive. (overproduction)
Individuals in a population vary extensively from each
other, mostly due to inheritance. (variation)
Struggle to survive: individuals whose inherited
characteristics best fit to environment leave more
offspring than less fit. (survival of the fittest)
Unequal ability of individuals to survive and reproduce
leads to gradual change in population. (adaptation)
Favorable characteristics accumulate over generations –
(descent with modification).
VIDEO CLIP:
https://www.youtube.com/watch?v=xkwRTIKXaxg
PBS: How does evolution really work? http://www.pbs.org/wgbh/evolution/educators/teachstuds/svideos.html
5.2.A2 Evolution of antibiotic resistance in bacteria.
5.2.A2 Evolution of antibiotic resistance in bacteria.
5.2.A2 Evolution of antibiotic resistance in bacteria.
5.2.A2 Evolution of antibiotic resistance in bacteria.
http://www.sumanasinc.com/scienceinfocus/a
ntibiotics/antibiotics_fla.html
VIDEO CLIP (stop at 5:15):
https://www.youtube.com/watch?v=W-WumllRPLI
Darwin’s Finches: Adaptive Radiation
One of Darwin’s most famous examples was the
evolution of the Galapagos finches. He noticed that
the finches on a set of neighboring islands were all
closely related, yet separate species.
He deduced that they had come from a single
population of finches on the mainland and had
probably been blown to their new habitats by a storm.
Each habitat had different selection pressures, so over
millions of years, the finches adapted to suit their own
islands. Eventually, they became separate species.
This is known as adaptive radiation.
http://www.pbs.org/wgbh/evolution/darwin/origin/index.html
http://www.sepa.duq.edu/finches.html
http://mrhardy.wikispaces.com/Natural+Selection.swf
5.2.A1 Changes in beaks of finches on Daphne Major.
Medium ground finch : Evolution in action
Variation: there is a
difference in the size and
shape of beaks
• Endemic to the Galapagos Islands
• Habitats are arid lowland forests and
shrub land.
• Generally feeds on seeds, but will also
feed on insects and the fruit of cacti.
Beak shape and size in Geospiza fortis
http://commons.wikimedia.org/wiki/File:Geospiza_fortis.jpg
5.2.A1 Changes in beaks of finches on Daphne Major.
Variation: there is a
difference in the size and
shape of beaks
Medium ground finch : Evolution in action
Beak shape and size in Geospiza fortis
1st Environmental change:
1974 to 1977 drought (La Niña)
conditions were experienced on
Daphne Major as a consequence
there was a shortage in smaller
sized seeds
2nd Environmental change:
1983 heavy and frequent rains
(El Niño event) were experienced
on Daphne Major as a
consequence there was an
abundance of smaller sized seeds
Deduce the results
from the graphs
https://coreybradshaw.files.wordpress.com/2011/02/figure1.jpg
http://commons.wikimedia.org/wiki/File:Geospiza_fortis.jpg