Summary of Lecture 1

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Summary of Lecture 1

• Comparative anatomy - living things are
  constructed along the same lines
• Taxonomy - life is hierarchical (tree of life)
• Geology - Earth is ancient, fossils record
  evolution, small changes can have big effects
• Biogeography - same environment yields different
  organisms

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2 Darwin and Wallace Proposed Two Theories of
Evolution
1. The living organisms we see today are all
related by descent (common ancestry)
2. The means by which evolution occurs is a
process of natural selection.

• organisms differ from one another i.e., there is
  variation
• these differences are heritable, i.e. passed from
  generation to generation
• many more organisms are born than survive and
  reproduce (mortality)
• therefore, any variation that makes one offspring
  more successful than another will have a greater
  chance of being passed to the next generation
  (survival of the fittest)

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3Population Dynamics (Malthus 1798)
Growth of human population versus growth in
resources
population

numbers

resources

time

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Reproductive ability
Heritable variation
Struggle for existence
Differential survival
Evolution
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Puzzles in Evolution

• Perfection
• Novelty

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5. Human eye is not perfect
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5a Blind spot

• Mark a piece of paper with a dot and a cross
  (about 3 inches apart)
• Hold at arms length, close your right eye, and
  look at the cross with your left eye
• Move the paper slowly towards you, always looking
  at the cross

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6. Hapless Gardener
Evolution cant see into the future
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6a Testis tubing
Actual condition in humans
If evolution could correct mistakes
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7. Recurrent Laryngeal Nerve
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OK, so life isnt perfect, but...

• We still need to explain complicated structures
  like the eye

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8 Evolution is like a safecracker

• To open this combination lock by guessing the
  complete combination is very hard (chance of
  guessing combination is 1 in 10,000,000,000).
• But, we can crack each wheel in turn. On average
  it will take five spins to get one wheel, so 50
  random trials will find the right combination.

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9 How to account for eyes
Examples of eyes from different animals
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Movie
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10 How to evolve an eye

• Shape of the eye changes at random by no more
  than 10
• Selection retains only those changes that improve
  optical performance of the eye
• 2000 steps would generate a vertebrate eye
• For realististic values of heritability and
  selection, this would take 400,000 generations
• If one generation one year, and eye takes less
  half a million years to generate

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10bSimulated evolution of eyes
Stages in eye evolution simulated on a computer
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How do we get new things evolving?
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11 Darwins finches are still finches
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12 Natural Selection can be conservative
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13 People have bred many kinds of pigeons but
they are still pigeons
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14 Ontogeny Embryos look more similar than
adults
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15 Are we apes that have not grown up?
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16 Gene duplications as source of novelty

• One copy of a gene, natural selection acts to
  conserve function
• but, if the gene duplicates
• Two copies, one retains the original function,
  the other may evolve a new function (or become
  junk)

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17Gene and genome duplication may have been
important in our evolution
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18 Puzzles in evolution

• How do we get complexity and perfect adaptation
  from random chance?
• adaptations are often not perfect
• evolution is like a safecracker
• evolution of the eye
• How do we get novelty?
• Changes in developmental timing
• gene and genome duplications

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20 The place of evolution in modern biology

• Control of pests by pesticides
• Bacteria and antibiotics
• HIV and AIDS - origins and clinical history of
  the disease
• Conservation biology - how do small populations
  survive and evolve?
• Darwinian medicine - how has human body evolved
  to cope with disease?

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21 Darwinian Medicine
Nothing in biology makes sense except in the
light of evolution Thedosius Dobzhansky
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22 Classical Medicine

• Tries to find the cause of a disease
• Seeks therapies to cure or relieve symptoms
• Studies proximate causes

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23 Darwinian Medicine

• Why is the body designed such that it is
  vulnerable to cancer, depression, choking, etc.?
• Why do we get old?
• Many symptoms may be natural defences - treating
  the symptoms may do more harm than good.

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24 Evolved Defenses

• Coughing clears the lungs
• People who feel no pain usually die young
• Feverish temperatures help kill pathogens
• Iron deficiency may be a means of depriving
  bacteria of iron
• Morning sickness limits the number of toxins a
  baby is exposed to

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25 The problem with genes for x

• Some want there to be a genetic basis for
  homosexuality so that they can argue that it's
  simply a natural biological phenomenon.
• Some want there to be a genetic basis for
  homosexuality so that they can argue that it's
  simply an aberrant biological phenomenon.

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26 Summary

• Natural selection is Darwins mechanism for
  evolution
• Evolution cannot see into the future -- there are
  limits to what it can do
• Many aspects of organisms are imperfect
• Understanding evolution will help understand
  disease, its origins and consequences