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Natural Selection
Or, how did we get here….
Natural Selection
• The Theory of Natural Selection is so simple that
anyone can misunderstand it…. (Anonymous)
• Charles Darwin (1809-1882) saw three problems in
need of a solution.
– Darwin was not the only one to see these problems BTW
– Other ‘Naturalists’ were struggling with the same issues
Problem the First
• There is change over time in the flora and
fauna of the Earth
– What we would commonly call ‘evolution’ today
– The fossil record showed this to be pretty clear,
even to people in the mid 1800s
– This was not controversial in Darwin’s time, and is
not now.
The Second Problem
• There is a taxonomic relationship among living
– People were big into classifying stuff
– It was pretty obvious that there was a relationship
between different species
• Different birds, different grasses, different cats etc
The Third Problem
• Adaptation
– Different kinds of teeth for different animals, say
carnivore ripping teeth and herbivore grinding
– Different tissues within species
• Heart vs. eye etc.
The Solution!
• Natural Selection provides a mechanistic
account of how these things occurred and
shows how they are intimately related.
• It is one of those ‘oh man is that ever easy,
why didn’t I think of that?’ type things.
How’s it work?
• There is competition among living things
– More are born or hatched or whatever, than survive and
• Reproduction occurs with variation
– This variation is heritable
– Remember, there was NO genetics back then, Chuck knew,
he just knew….
– Realized that is wasn’t ‘blending’
How’s it Work?
• Selection Determines which individuals enter
the adult breeding population
– This selection is done by the environment
– Those which are best suited reproduce
– They pass these well suited characteristics on to
their young
How’s it Work?
• REPRODUCTION is the key,
not merely survival
• If you survive to be 128
but have no kids, you are
not doing as well as I am
• I have reproduced…
• Assuming the traits that
made me successful will
help them then I amore fit
NOW than the 128 year
old guy
This lecture keeps evolving…..
• Survival of the Fittest (which Chucky D NEVER said)
means those who have the most offspring that
• So, the answer to the trilogy of problems is:
• ‘Descent with modification from a common ancestor,
NOT random modification, but, modification shaped
by natural selection’
Different types of selection
• Directional Selection
• What most of us think
about when we think
about selection
• An extreme value is
selected for
• Human brain size is a
nice example
Different kinds of selection
• Stabilizing or
Normalizing selection
• The middle is selected
• Many examples here
– Symmetry
– Two eyes
Different kinds of selection
• Disruptive selection
• Extremes are selected
• Might be where the
two sexes come from
• Trait was probably
gamete sized
• Two ‘mating types’
Other Evolutionary Theories
• Lamarckism
– Inheritance of acquired characteristics
• E.g., giraffes really wanted leaves, so they stretched their necks
• Sounds crazy, but a lot of people think this way
• ‘We will all have giant heads and tiny bodies someday’
• ‘Cave swelling fish don’t use their eyes so they disappear’
• ‘We don’t use our appendix so it is disappearing’
Silly incorrect evolutionary theories and
• Orthogenesis
There is some plan to evolution.
The idea of an ‘evolutionary ladder’ fits in here
It is wrong too……
Still another silly idea
• Intelligent Design
• Just Creationism with a fancy name
• God does not belong in a science class, any
more than experiments belong in church