The Theory of Evolution
(See Chapter 16 in your text)
Understanding Natural Selection
Evolution
Theory
What do these words mean?
What is a theory?Common English
languageA theory is...
A best guessA hypothesisSomething you
aren’t sure about
Science
A theory is...The result of many
experiments that all show the same thing
NOT a guessNo evidence has
been found against it
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
What is evolution?
Which genes had better evolutionary fitness?
Before the industrial revolutionAfter the industrial revolution
What happened to the population over time?
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?
What does a population need so it can evolve?
1. Inherited Variation
1. Inherited Variation2. Overproduction
What does a population need so it can evolve?
1. Inherited Variation2. Overproduction
3. Struggle to Survive
What does a population need so it can evolve?
1. Inherited Variation2. Overproduction
3. Struggle to Survive4. Successful Reproduction
What does a population need so it can evolve?
Thomas Malthus (late 1700s)
Is there enough food for all?
Years
Units of
FoodPopulationSize
Malthus said:At some point,
we will run out of food!
Charles Lyell – Principles of GeologyThe earth is very oldMany small changes over a long time can
produce big differences
How old is the Earth? How long does it take to change?
History of the theory of Natural Selection
How did the giraffe get its long neck?
(Early ideas about natural
selection)
History of the theory of 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 onYou can only pass on what is in your DNA
(which doesn’t change)
What do you think? Is that true?
Voyage of the Beagle (1831 – 1836)
Looked at specimens from all over the world
Saw similarities and differences and tried to explain them
Charles Darwin
Voyage of the HMS Beagle
What did Darwin see?Famous example of
finches in the Galapagos Islands
Each slightly different with different food sources
How did the finches get that way?Ancestor finch arrives on
an islandFinches 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...
But Darwin was not the only one!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
Why did Darwin wait more than 20 years to publish his ideas?
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?