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 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
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
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’
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’
Other Evolutionary Theories
 Lamarckism
 Inheritance of acquired characteristics
 E.g., giraffes really wanted leaves, so they stretched their
necks and…..
 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 ideas
 Orthogenesis
 There is some plan to evolution.
 NO WRONG INCORRECT, THANKS FOR
PLAYING
 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
 NOT A SCIENTIFIC THEORY