Lamarck Vs. Darwin

1
Lamarck Vs. Darwin

• Dr. Edelberg

2
Early Ideas-Before Darwin Lamarck

• Earth was relatively young (6000years)
• Livings things were created perfectly from the
  beginning
• Earth and living things remain unchanged

3
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
• Lamarcks hypothesis was wrong

4
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

5
Evolution of long legged birds

• Snowy Egret

• Great Blue Heron

6
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.

7
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

8
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

9
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

10
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
  Lamarcks theory and which scenario is consistent
  with Darwins theory
• TO BE HANDED IN

11
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

12
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