Download 3 – Understanding Natural Selection

The Theory of Evolution
(See Chapter 16 in your text)
Evolution
Theory
 Common English
 Science
language
A theory is...
A theory is...
 A best guess
 The result of many
 A hypothesis
experiments that all
show the same thing
 NOT a guess
 No evidence has been
found against it
 Something you aren’t
sure about
 The processes that have transformed life on earth from it’s
earliest forms to the vast diversity seen today.
 A change in the genes!
 MANY experiments and observations show the same
conclusion
Before the industrial revolution
After the industrial revolution
 Which moths were the




most common after the
trees changed?
Why did the population
change?
Could individual
moths change color?
How would you observe
this in the local
environment?
Did a new species form?
1. Inherited Variation
1. Inherited Variation
2. Overproduction
1. Inherited Variation
2. Overproduction
3. Struggle to Survive
1. Inherited Variation
2. Overproduction
3. Struggle to Survive
4. Successful
Reproduction
 Thomas Malthus (late 1700s)
Units
of Food
Population
Size
Malthus said:
At some point,
we will run out
of food!
Years
 Charles Lyell – Principles of Geology
 The earth is very old
 Many small changes over a long time can produce big
differences
 How did the
giraffe get its
long neck?
(Early ideas about
natural selection)
 Jean-Baptiste de
Lamarck (1809)
 If an organism uses a
body part it will get
stronger
 Then it can pass on
that trait to its
offspring
 Acquired characteristics CAN’T be passed on
 You can only pass on what is in your DNA (which
doesn’t change)
 Voyage of the
Beagle (1831 –
1836)
 Looked at
specimens from
all over the
world
 Saw similarities
and differences
and tried to
explain them
 Famous example of
finches in the Galapagos
Islands
 Each slightly different
with different food
sources
 Ancestor finch arrives on




an island
Finches spread to different
islands, each with a
different type of food
Birds with beaks that eat
the food best survive better
and reproduce more
There are more birds with
the right kind of beak on
that island
Continues for many years...
 Another (younger)
scientist was studying
the same thing
 Alfred Russel Wallace
came up with the theory
of Natural Selection too
 Sent a letter to Darwin
asking advice
 They published the idea
together...
http://www.pbs.org/wgbh/nova/darwin/program-q-300.html
 Darwin started thinking
about Natural Selection
in 1836
 He published The
Origin of Species in
1859
 Why did he wait so long?
What do you think?