Lamarck Vs. Darwin
Dr. Edelberg
Early Ideas-Before Darwin &
Lamarck
• Earth was relatively young (6000years)
• Livings things were created perfectly from
the beginning
• Earth and living things remain unchanged
Jean Baptist Lamarck
• One of the first to state living things change
over time
• Proposed a mechanism for how organisms
change over time before Darwin did and
called it inheritance of acquired traits
• Lamarck’s hypothesis was wrong
Two ideas on how living things
evolve
• Consider the long legs of wading birds
• How could such a bird evolve long legs?
• Read Scenario A and B on the following slides
and then answer the questions that follow the two
scenarios
• When reading the two scenarios, assume the
species ancestral to long legged birds had short
legs and could only wade in shallow water along
the shore eating snails and small fish
Evolution of long legged birds
• Snowy Egret
• Great Blue Heron
Scenario A
• A change in the environment increased
competition between the birds resulting in
depletion of food supply in the shallow waters
• This caused a need for the short leg birds to wade
into deeper water in order to get food to survive
• This forced them to stretch their legs, which
caused their legs to get a little longer
• When the birds produced offspring, the baby birds
grew with slightly longer legs inherited from their
parents.
Scenario A-continued
• These offspring birds needed to wade out even
farther, so they stretched their legs even more and
made their legs a little bit longer
• In turn, their offspring grew up with even longer
legs inherited from their parents
• Eventually, after many generations of this process,
the legs of these birds were so much longer than
the ancestral birds, that the new birds could be
described as a new species
Scenario B
• Within the species of ancestral short legged
shorebirds there is a range of leg lengths from a bit
shorter to a bit longer than the average leg length
• A change in the environment increases
competition between the birds, depleting the food
supply in the shallow water
• The birds with the slightly longer legs could wade
out a little farther
• As a result, they obtained more food, lived a little
longer, and therefore produced more offspring
Scenario B-continued
• Those birds with the shorter legs would tend to
starve to death
• Since the tendency for leg length was already
inheritable, the surviving longer leg birds tended
to have more longer leg offspring
• Eventually, after many generations of this process,
the average leg length of the birds was so much
longer than the ancestral birds that the new birds
could be described as a new species
Comparing Scenarios
• Compare and contrast the two scenarios
• Which scenario seems more accurate?
• Cite statements that seem false and explain
why
• Hypothesize which scenario is consistent
with Lamarck’s theory and which scenario
is consistent with Darwin’s theory
• TO BE HANDED IN
Comparing Lamarck and Darwin
• Lamarck and Darwin: Summary of theories
• Click on link above and then click on each
link below until you have read all 4
associated pages (How they agreed, What
Lamarck believed, What Darwin believed
and Why we believe Darwin.
• After studying differences click on next
slide
Comparing Darwin and Lamarck
• Which scenario now sounds like an explanation
that Darwin might give? Why?
• Which scenario now sounds like an explanation
that Lamarck might give? Why?
• What are the specific clues that most clearly
distinguishes a Darwinian explanation from a
Lamarckian explanation?
• What explanation is most likely correct?
• TO BE HANDED IN