Download Powerpoint on Natural Selection

Darwin’s Tea Party
The Theory of Evolution by Natural Selection
Charles Darwin (1809-1882)
Last update 8 Oct, 2009
Biological Evolution
Definition:
“Change in the genetic composition of a
population during successive generations
(due partly to natural selection) and resulting
in the development of new species”
(Wesbter’s).
Biological Evolution
The ancestors of the horse, for
example, have undergone
considerable change in
physical size and proportions
over the last 60 million years.
Biological Evolution
• The adult size, shape,
bones, internal organs
and many other physical
and behavioural features
have changed.
• The original Eohippus was
thus a different “type of
animal” (species) than
the present day horse
(Equus)
Evolution and Genes
Such changes in body parts are the
result of changes in genes.
When nature “selects” the “fittest”
for survival and reproduction, it is
also selecting the fittest
combination of genes to survive
and reproduce.
These come “packaged” in a
creature’s body.
Evolution and Genes
• Thus Biological Evolution
happens through the
transmission of genetic
characteristics from one
generation to the next.
• Individuals who are the most
genetically “fit”, survive to
reproduce (called natural
selection or “survival of the
fittest”) and pass on their fit
characteristics.
Evolution and Genes
• During Darwin’s time not much was known
about genetics.
• But Darwin did know that variation existed.
• That was enough to establish that in every
species only those individuals that had
favourable variations would be more fit and
thus live on and reproduce.
Evolution by Natural Selection
• Natural selection is not the same as
evolution
• Natural selection is one cause of
biological evolution.
• It is like an “engine” that drives
evolution on.
Evolution by Natural Selection
• “Natural selection” is a metaphor which
Darwin compared to “artificial selection”
(the breeding of plants & animals).
• In “artificial selection”, humans “select”
which individual plant or animal will
reproduce.
• In natural selection, “nature” does this
“selecting”.
Natural & Artificial Selection
• In fact, Darwin begins
his Origin by discussing
the artificial selection
(breeding) of pigeons.
• In this example, we can
see how three radically
different looking breeds
of pigeon (Pouter,
Jacobin and Fantail)
have been produced by
artificial selection from
the original Wild Rock
pigeon.
Natural & Artificial Selection
Varieties of bananas
produced by artificial
selection
Natural & Artificial Selection
Note how all these
dramatically different
vegetables were
created by artificial
selection from an
original ancestor.
Natural Selection
How does it work?
Natural Selection is like a machine
with 3 parts:
1. Variation
The tendency for individuals in a species to differ
slightly from their parents and from each other.
2. Population Pressure
the tendency for population growth to outstrip
available resources
3. Deep Time
The discovery that the earth (and life on it) was
far older than had previously been thought.
1. Variation
1. Variation
The tendency for individuals in a species to
differ slightly from their parents and from
each other.
1. Variation
Will this be
on the test?
Variation
among high
school students
1. Variation
You
mean I
was
adopted
?
Variation
within a family
(not the dog –
it’s a different
species)
1.
Variation
They
think
were cute
now
But wait
till they
see their
couch
Variation
between house
cats (felis
domesticus)
1. Variation
The exact causes of
variation were
discovered only after
Darwin’s death. The
discovery was made by
the Austrian monk
Gregor Mendel, the
father of modern
genetics.
I love
peas
Gregor Mendel (1823-1884)
1. Variation
• One cause of variation is sex - the combining of
the genetic material of male and female to create
offspring. (Also called sexual recombination)
• Another cause was mutation - accidents to the
genetic material
• Variation is NOT caused by population increase or
by the environment or by use/disuse, etc…
1. Variation
• Variation means there are different
degrees of fitness among individuals in a
population of the same species.
• Some happen to be born with
advantageous variations (giving them
added fitness) and others not.
2. Geometrical Population Increase
2. Geometrical Population Increase
The tendency for a population of any given
species tends to outstrip the available
resources necessary to keep it alive.
As Darwin says,
“More are born than can possibly survive”.
2. Geometrical Population Increase
Want less
poverty? STOP
HAVING
SEX!!!
The “principle of
population” was first
expressed by the
British political
economist, Reverend
Thomas Malthus.
Thomas Malthus (1766-1834)
2. Geometrical Population Increase
Time
In the human world,
Malthus said,
population tends to
increase at a
“geometric” rate
while resources
increase only at an
“arithmetic” rate.
Malthus’ Concept of Geometric
Population Increase (GPI) in the
human world:
Population
Resources
Population
2. Geometrical Population Increase
 Given this geometric rate of increase, part
of the human population is bound to be poor
or even die.
 As Malthus states,
“...more will always be in want than can
actually be supplied”.
2. Geometrical Population Increase
 Darwin applied Malthus’ idea of geometric
population increase to the entire living world.
 He saw that it would lead to a “struggle
for survival” continuously occurring
between individuals in nature.
2. Geometrical Population Increase
This “struggle for survival” would leave only
the “fittest” individuals to survive (those with
favourable variations) and reproduce
Thus:
GPI + V = NS (natural selection also called
“the survival of the fittest”).
2. Geometrical Population Increase
• By “fit” Darwin meant
not just the
“strongest” but those
best adapted to the
environment
• These would tend to
leave more offspring
behind than the less
fit.
3. Deep Time
3. Deep Time
Deep time is the theory that the earth – and
life on it – have been around for much, much
longer than previously thought.
3. Deep Time
• Given sufficient time (deep time) natural
selection will have “weeded out” so many
unfavourable variations and accumulated
so many favourable variations that a new
species will have developed from a
previous ancestor.
3. Deep Time
• Evolution by Natural Selection thus
required millions of years to transform
small changes into big ones.
• But many naturalists believed that the
Earth was only about 6,000 years old.
3. Deep Time
The Irish Archbishop James Ussher (15811656) calculated the age of the earth
according to what he believed the Bible
indicated.
3. Deep Time
I’m a
YEC!
Archbishop James Ussher (1581-1656)
• According to Ussher
the universe began on
Sunday, 23 October
4004 BC at 9:00 AM.
• This was not enough
time for evolution to
have occurred
Geology
Rocks!
3. Deep Time
• But by the 19th century,
the science of geology
confirmed that the earth
was actually millions of
years old.
• Key was geologist Charles
Lyell’s book Principles of
Geology which Darwin
had read on the Beagle.
Charles Lyell (1797-1875)
3. Deep Time
• Thanks to Lyell and the science of geology,
the earth – and life on it – were proven to be
much older than anyone previously thought
• For Darwin deep time was a key to
acceptance of his evolutionary theory
which required a huge time scale.
3. Deep Time: The Grand Canyon
3. Deep Time: The Grand Canyon
6000 feet deep at its lowest and 15 miles across at its widest.
The Colorado river has cut into the Canyon, exposing almost 2
billion years of earth’s history.
The Canyon’s geological structure shows it was made by a very,
very long process of erosion by wind and water as well as
volcanic activity and other geological processes.
3. Deep Time
This chart gives
us some idea of
the scale of deep
time. Note how
recent is the
arrival of Homo.
3. Deep Time
• Another way of
visualizing deep
time
• Note the many
periods of
glaciation
• Note the changes
in the shape and
position of
continents
Summary: Natural Selection
• Geometrical Population Increase (GPI)
 causes “struggle for survival” (meaning only
some individuals will live and reproduce)
• Variation (V)
causes differences in fitness b/w individuals
THUS:
GPI + V = “survival of the fittest” (natural
selection)
Summary: NS + Deep Time
Natural Selection
+
Deep Time
=
Biological Evolution
Cast of characters
Charles Darwin (1809-1882)
Founder of theory of evolution by natural selection
Charles Lyell (1797-1875)
Discoverer of ‘deep time’
Thomas Malthus (1766-1834)
Articulates the ‘principle of population’
Gregor Mendel (1823-1884)
Founder of science of genetics
The End
Written & Directed by
Gabriel Tordjman