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