Charles Darwin developed the theory of natural selection after observing variations in finch beaks on the Galapagos Islands. Natural selection has four parts: overproduction of offspring, inherited variation of traits, struggle for survival, and successful reproduction of adapted organisms. Darwin lacked an understanding of genetics and the source of variations, but we now know traits are inherited from parents and variations arise from gene combinations. Natural selection can act through factors like hunting, resistance, and competition to change population levels over time and potentially lead to the formation of new species.

1. How Does Evolution
Happen?
(Natural Selection)

2. First man to explain
o Charles Darwin
o Took a five year voyage
around the world after he
got out of college
o Served as a naturalist on
the British ship HMS Beagle
o Formed a theory of how
evolution happened
o Collected plant and
animal samples on his
travels
o Visited the Galapagos
islands just west of
Ecuador (South America)

3. Map of the Galapagos Islands

4. Galapagos Island Discoveries
o Found that the finches on these
islands were similar to Ecuador’s
o Each island was still a little
different from the next
o Found that the beaks of the
finches had adapted to their
food source on the different
islands.

5. Finches

6. Darwin starts to think..
o How did we get these similar species?
o He had ideas about the Earth
o He found that Earth has been formed by natural
processes over a long period of time
o He had ideas about breeding
o Selective breeding- breeding plants/animals to
have desired characteristics
o He had ideas about populations
o Realized that any species can produce many
offspring, but they are limited by several
factors.

7. What limits offspring?
o Starvation
o Disease
o Competition
o Predation
o He found that really only a limited
amount of individuals will survive to
reproduce.
o There is something unique about the
survivors. They must have stronger
genetic traits. Those are the traits that will
pass down to their offspring.

8. Darwin’s thinking lead to his theory of Natural
Selection
o Once he returned from his voyage, he
thought for 20 yrs about the observations
he had taken from the world and wrote a
book called On the Origin of Species by
Means of Natural Selection.
o Darwin’s theory of natural selection is the
process by which individuals best
adapted to their environments survive
and reproduce more successfully than
less well adapted individuals
o This theory of natural selection is broken
into four parts.

9. Four Parts of Natural Selection
o 1) Overproduction
oOrganisms will give birth to
thousands of offspring realizing
that some will become adults and
others will not.
o 2) Inherited Variation
oEvery individual has its own
combo of traits. (similar to parents)

10. Continued
o 3) Struggle to Survive
oPredators, starvation,
diseases
o 4) Successful Reproduction
oThe organisms best adapted
in their environment will
produce the most surviving
offspring.

11. Think About it…

12. Darwin Lacked
o When Darwin was introducing his
theory of natural selection he
lacked two important things:
o 1- He didn’t know how we inherit
traits
o 2- He didn’t know how the
variations occurred
o We have learned how both of these
occurrences happen, tell me how!

13. Yes??
o 1) We inherit traits from our parents
when they get passed down to the
offspring.
o 2) Variations occur because of the
different gene combinations that can
be made when the mother and
father come together to produce
offspring.

14. Natural Selection in Action
o A population changes in
response to its
environment.
o Things that can affect an
environments
population are:
o Hunting
o Resistance
o Competition

15. Hunting
o A new affect such as hunting
can play a role in how a
population level rises or falls.
o In 1930 Uganda’s male
elephant population that
contained tusks was 99% and
only 1% of them were born
without them. Today 85% of
male elephant population
contains tusks.
o Because of this, more of the
tusk less elephants are
surviving and reproducing.
This trait does get passed
down.

16. Resistance
o Some organisms such as insects can
build resistance to certain chemicals.
o This can send an increase in a
particular insects population that
could be harmful.
o It doesn’t take long for insects to build
up this resistance and reproduce.
o Generation time: the period between
the birth of one generation and the
birth of the next generation.

17. Competition
o Many species will
have competitions for
their mates
o Some organisms may
over time have some
interesting
adaptations.
o Feather colors, smells,
dances, sounds, etc.

19. Forming a New Species
o May form if the groups get separated
from the original population.
o The two groups can adapt to their
environments and get to a point
where they are so different they
can’t even mate anymore.
o A new species is a result of evolution.
We call this speciation.
o Separation-Adaptation-Division