This is a widescreen fully animated and editable PowerPoint presentation that covers section 2.3 of the Cambridge Pre-U Biology course. It is 55 slides long and covers the following topics: Darwin and Wallace Natural Selection Effect of climate change and extinction Speciation Resistance The full PowerPOint can be downloaded here: https://sellfy.com/p/tUdn/#

1. MAKING SENSE OF
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2. Copyright © 2017 Henry Exham
• Understanding evolution is critical to understanding biology.
• Evolution explains how primitive life forms evolved into the
incredible diversity of life on our planet today.
• Evolution is therefore the story of life on earth and the fossils
we have found are some of the pages from that story.
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By Pakicetus_BW.jpg: Nobu Tamura (http://spinops.blogspot.com)Ambulocetus_BW.jpg: Nobu Tamura (http://spinops.blogspot.com)Kutchicetus_BW.jpg: Nobu
TamuraProtocetus_BW.jpg: Nobu TamuraJanjucetus_BW_(mirrored).jpg: *Janjucetus_BW.jpg: Nobu Tamura email:nobu.tamura@yahoo.com
www.palaeocritti.comderivative work: Niusereset (talk)Squalodon_BW.jpg: Nobu Tamuraderivative work: Niusereset - This file was derived from:Pakicetus
BW.jpg:Ambulocetus BW.jpg:Kutchicetus BW.jpg:Protocetus BW.jpg:Janjucetus BW (mirrored).jpg:Squalodon BW.jpg:, CC BY-SA 3.0,
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This image shows just
one part of the story of
how whales evolved
from four legged
terrestrial mammals.

3. MAKING SENSE OFMAKING SENSE OF
Darwin, Wallace and Natural Selection
Environmental Stress and Extinction
Speciation and Resistance
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4. Copyright © 2017 Henry Exham
a) Outline Darwin’s and Wallace’s observations and conclusions.
b) Describe evolutionary patterns of divergence and adaptive
radiation, including the Galapagos finches as an example.
c) Outline the mechanisms leading to evolutionary changes in
allele frequency in populations, including the role of
mutation in producing genetic variation and how such
variation might enable organisms with particular alleles and
particular phenotypes to survive better and reproduce more.
d) Describe and explain directional, stabilising and disruptive
selection.
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5. Copyright © 2017 Henry Exham
• Evolution is the change in the heritable
characteristics of biological populations over
successive generations.
• Charles Darwin is often hailed as the person who
formulated the theory of evolution.
• However, the theory was first officially presented
to the Linnaen society as a joint paper with Alfred
Russel Wallace in 1858.
• The idea of evolution wasn’t completely new but
what they proposed was a method by which it
could occur. They called the process natural
selection.
The Darwin–Wallace Medal is a medal
awarded by the Linnean Society of London
for major advances in evolutionary biology.
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6. Copyright © 2017 Henry Exham
• They had worked independently but arrived at the same conclusions.
• Wallace accumulated evidence to support his ideas from the
Amazon and the Malay Archipelago.
• Darwin accumulated evidence supporting the idea that living
organisms change with time from
o The Galapagos Islands
o Geological Evidence
o Fossil Evidence
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7. Copyright © 2017 Henry Exham
• Darwin ended up getting
more fame as he had a
bigger body of evidence and
a deeper development of
the idea of natural selection
which is the process which
causes evolution.
• He outlined this in his
famous book ‘On The Origin
of Species by means of
natural selection’ first
published in 1859.
By http://wellcomeimages.org/indexplus/obf_images/5a/0d/2a5828b7413ab746df351239d975.jpgGallery: http://wellcomeimages.org/indexplus/image/L0051514.html,
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8. Copyright © 2017 Henry Exham
• The main observations and ideas that lead Darwin and
Wallace to the theory of natural selection were:
• These are expanded upon in the following slides.
Fecundity
Variation
Survival rates Inheritance
Population sizes
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9. Copyright © 2017 Henry Exham
• Fecundity is the reproductive rate of
an organism.
• They noticed that organisms tend to
overproduce.
• However the population size doesn't’t
really change.
Fecundity and Populations 1
4
16
For example a robin usually
lays a clutch of 4 eggs. If these
all survive and lay 4 more
each then there would be 16.
If this continues for 10
generations there would be
1,048,576 robins.
That doesn’t happen!
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10. Copyright © 2017 Henry Exham
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11. This PowerPoint is protected under copyright.
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