Download 5_Week_of_February_6-11,_2012__files/Natural Selection PPT

Natural Selection
Or, how did we get here….
Key concepts:
• Communicate scientific understandings using
descriptions, explanations, and models
• Explain why variation within a population can
enhance the chances for group survival
• Analyze how structural behavioral, and
physiological adaptations within a population
enable it to survive in a given environment
Key Vocabulary:
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Species
Population
Adaptation
Natural selection
Selective Breeding
Time out for vocabulary:
• Natural selection: the process by which individuals
that are better adapted to their environment survive
and reproduce more successfully than less well
adapted individuals do
• Adaptation: a characteristic that improves an
individual’s ability to survive and reproduce in a
particular environment
• Species: a group of organisms that are closely
related and can mate to produce fertile offspring
• Population: group of individuals of the same species
in the same place
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 things
 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 teeth
 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 reproduce
 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
Parts:
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
 Say that I, I have
reproduced…
 Assuming the traits that
made me successful
will help them then I
amore fit NOW than the
127 year old guy
This lecture keeps
evolving…..
 Survival of the Fittest (which Chucky D
NEVER said) means those who have the
most offspring that reproduce
 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’
SOOOOOO…what does it
mean…
 Evolution is a change over time in a
population of organisms…they have to
reproduce in order to pass the traits…
 Turn to page 115--Insects
Human intervention:
 Dog breeds…how did we do it?
 Breed dogs of certain qualities with other
dogs with traits we wanted…
 Continued to do this and we get a dog that
we want.
What does this mean:
 Our traits will change over time in order
to BETTER adapt to what is going on in
our environment
 This can lead to changes in species and
even the making of a new species…
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 for
 Many examples
here
 Symmetry
 Two eyes
Different kinds of selection
 Disruptive selection
 Extremes are
selected for
 Might be where the
two sexes come
from
 Trait was probably
gamete sized
 Two ‘mating types’
What does it all mean?
 Evolution is
driven by
NATURAL
selection.
 What did your
moth simulation
tell you?