Lamarck vs. Darwin
Introduction to change in
organisms
What is a theory?

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The most probable
explanation for a large
set of data based on the
best available evidence
Summarizes a hypothesis
or group of hypotheses
that have been supported
with repeated testing
What is a species?
What is a population?

Species – group of a
single type of organisms
that interbreed and are
reproductively isolated


White-tailed deer
Population – refers to a
group of organisms of a
particular species living in
a certain area.

White-tailed deer on Mt.
Nebo
Lamarck’s Theory

Jean Baptiste Lamarck: 1800’s

Believed:
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Change Occurs Over Time
inheritance of acquired
characteristics
 acquired changes were passed to
offspring
Law of Use and Disuse
 If a body part were used, it got
stronger
 If body part NOT used, it
deteriorated
Examples: Body builders or pierced
ears
Lamarck’s Theory of Evolution

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Giraffes all had SHORT
necks originally
Giraffe’s Necks got
LONGER from stretching
for food
“Acquired” trait (long
necks) then passed to
offspring
Giraffe population
became long-necked
Lamarck’s Theory of Evolution

More examples

Traits Acquired During Ones Lifetime Would
Be Passed To Offspring
Clipped ears and tails of dogs could be passed to offspring!
Lamarck’s Mistakes

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Was he correct??
 NO!
Traits are passed down from one
generation to the next by GENES, not by
an individual’s life experiences or
activities
Lamarck did NOT know how traits were
inherited (Traits are passed through
genes)
Genes Are NOT Changed By Activities In
Life
Change Through Mutation Occurs Before
An Organism Is Born
Voyage of the Beagle
Charles Darwin

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Born Feb. 12, 1809
Joined Crew of HMS
Beagle, 1831
Naturalist
5 Year Voyage around
world
Astounded By Variety of
Life
Voyage of the Beagle
During His Travels, Darwin Made
Numerous Observations And
Collected Evidence That Led Him
To Propose A Revolutionary
Hypothesis About The Way Life
Changes Over Time
Darwin’s Belief’s

Survival of the fittest OR
natural selection
Food and resources are
limited
 So organisms have to
COMPETE to get them
(lions fight for food,
space, mates …)
• OVER PRODUCE too many
organisms
• Not all offspring will survive
only the MOST FIT (not
always the strongest!)

What happened to the
giraffe’s?

Survival of the fittest or natural
selection
 Natural selection said the giraffes
with short necks had less food to
eat
 Why?

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the food resources changed to leaves only
on the upper branches
What happened?


short necks could not reach upper branches
and did not survive (couldn’t pass on genes)
Long neck giraffes survived & reproduced
because they were able to reach the food
• Evolution is
the slow, gradual
change in a
population of
organisms
over time…
a looooooooong time!

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When there is an unequal ability of
individuals to survive and reproduce …
This leads to a gradual change in a
population with favorable characteristics
accumulating over generations
Most fit “naturally” selected
New species evolves
Natural Selection

How does Selection occur?
 Selection of the most fit can occur
from several factors:
 Variations exist among individuals in a
population
 Competition for limited resources
 Overpopulation
 Predation/Disease
Example of Natural Selection

A classic example of natural selection
is the Peppered moths during
Industrial Revolution in Europe