Transcript Natural Selection

Darwin’s Theory of Evolution
by Natural Selection
The 9 Basic Points
Point # 1
A population of organisms has the
potential to increase its numbers
at a geometric rate.
It’s not hard to imagine each individual breeding
to produce 2 offspring…so let’s do some math:
Start with 2 individuals, multiply by 2 for their
offspring = 4.
Multiply that by 2 for the next generation = 8.
Generation 3 = 16.
Continue this way to generation 10.
How many did you get?
2048
By generation 20, there will be over 2 million
individuals!!
Point # 2
In the short run, the number of
individuals in a population
remains fairly constant.
We don’t usually see a population of
organisms take off like our calculations
would suggest.
Point # 3
The conditions of life are limited.
What are some of the things that might put a
limit on how many organisms can live in a
place?
Food? Water? Shelter? Predators?
Competitors? Can you think of others?
Point # 4
Only a fraction of the offspring in a
population will live to produce
their own offspring.
Why? Think about point
# 3. Why might they
not all survive?
Point # 5
Individuals in a population are not
all the same: some have
variations that they inherited.
What are some of the
inherited variations that
exist in the human species?
Point # 6
Life activities and the struggle to
stay alive determines which traits
are favorable or unfavorable by
determining the success of the
individuals who possess the traits.
Example: being hunted may cause a trait for
better camouflage to be favorable since
those with that trait will survive better.
http://www.teachersdomain.org/9-12/sci/life/evo/camouflage/index.html
Point # 7
Individuals having favorable traits
will, on the average, produce
more offspring than those with
unfavorable traits.
And why do you think being able to
produce offspring is important in natural
selection?
Point # 8
The environments of most
organisms have been in change
throughout geologic time.
What is meant by geologic time?
Radioactive dating tells us the age of the
earth is about ~4.5 billion years old and the
fossil record tells us that living things have
only been here the last 3.5 billion years
To demonstrate how long that is
If we use a single year as an analogy to
represent the 3.5 billion years life has been
on earth, modern humans only came into
the picture during the last 2.5 hours on the
last day of December.
What might be some good evidence that
environmental changes have occurred over
that time period?
Point # 9
Natural selection causes the
accumulation (buildup) of new
variations and the loss of
unfavorable variations to allow
species to become better suited
to a particular environment and
new species arise.
These 9 points make up the
backbone of the theory of natural
selection.
Natural selection is said to be the
driving force behind evolution…in
other words, natural selection is
what makes change over time
happen.