Name ____________________ Period _______
Accelerated Biology
Darwin vs. Lamarck
Lamarck
Organisms constantly strive to improve themselves and
become more advanced.
The effort to improve causes the most used body structures to
develop, while unused structures waste away.
Once a structure is modified by use or disuse, the
modification is inherited by the organism’s offspring.
Darwin
There is variation within populations. Some variations are
favorable, improving the organism’s ability to function and
reproduce in its environment.
More young are produced in each generation than can survive.
Only a few offspring live long enough to reproduce.
Organisms that survive and reproduce are those with
favorable variations. Because the offspring of these
individuals will inherit favorable variations, a larger and
larger proportion of each new generation will have these
variations.
Over enormous periods of time, small changes accumulate,
and populations change.
PART A Use the information in the table and diagram to answer the following questions.
1. What is the second part of Lamarck’s theory of evolution called?
The theory of use and dissue
2. Which part of Darwin’s theory of evolution explores natural selection?
Organisms that survive and reproduce are those with favorable variations (the
environment selects the organisms that are best adapted to survive)
3. What is gradualism?
When species evolve slowly over time
4. Which part of Darwin’s theory of evolution includes the idea of gradualism?
Over enormous periods of time, small changes accumulate, and populations change.
5. Millions of years ago, giraffes had necks of different lengths as shown in the first part of each
diagram. Explain how giraffes would have developed long necks according to Lamarck’s ideas about
evolution. Then, explain how giraffes developed long necks according to Darwin’s ideas about
evolution.
Lamarck – Throughout a giraffe’s lifetime, they are constantly USING their necks
muscles to stretch and reach the leaves high up in the canopy of the trees. As adults,
they have ACQUIRED long necks. This acquired trait can be passed on to their
offspring.
Darwin – Some giraffes neck are slightly longer than others. During times when food is
scarce, the giraffes that are best adapted to the environment (long necks) will live
longer and reproduce more, thus passing on the beneficial traits to their offspring.
Consider the long legs of wading birds such as herons and egrets, birds that are common around rivers
and marshes of Illinois. How could a bird evolve such long legs? Read the two scenarios and discuss each
with your group. After reading and discussing both scenarios, answer the questions that follow.
Great Blue Heron
Snowy Egret
Assume that the species ancestral to these birds had short legs, and could only wade into very shallow
water along the shoreline, eating snails and small fish.
Scenario A
A change in the environment increased competition between the birds, and resulted in a depletion
of the food supply in the shallow waters. This created a need for the short–legged birds to wade into
deeper water in order to survive, which forced them to stretch their legs, because they didn’t want to get
knocked over by the little waves. This stretching caused their legs to get a little longer.
When these birds produced hatchlings, the baby birds grew up with slightly longer legs inherited
from their parents. These offspring birds needed to wade out even farther, so they stretched their legs even
more, and made them a little bit longer yet. In turn, their hatchlings grew up with even longer legs
inherited from their parents, and so on . . .
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 shore birds, there is a range of leg lengths, from a bit
shorter to a little bit longer than the average leg length. These leg lengths tended to run in the families
(i.e., leg length was hereditary).
A change in the environment increases competition between the birds, depleting the food supply in
the shallow waters. 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 hatchlings. Those with the shorter
legs would tend to starve to death. Since the tendency for leg length was already inheritable, the surviving
long–legged birds tended to have more long–legged hatchlings, which likewise tended to get more food
and produce more hatchlings and so on . . .
Eventually, after many generations of this process, the average leg length of these birds was so
much longer than the ancestral birds that the new birds could be described as a new species.
Answer these questions based on the scenarios presented.
1. Which scenario sounds like an explanation that Darwin might give? Support your answer.
Scenario B – It states . . .
 Birds have legs that are different lengths (variation)
 There is increased competition for food (struggle for existence)
 Birds with the long legs get more food (survival of the fittest)
 Long legged birds produce more hatchlings (descent with modification)
2. Which scenario sounds like an explanation that Lamarck might give? Support your answer.
Scenario A – It states . . .
 Birds STRETCH their legs making them longer
 This ACQUIRED trait is then passed on to their offspring – NOT!!!
3. What are the specific clues that most clearly distinguish a Darwinian explanation from a Lamarkian
explanation?
Lamarck – Acquired traits can be passed on
Darwin – Individuals that are best adapted to the environment will live longer and
reproduce more, thus passing on the beneficial traits to their offspring
4. Go back to the two scenarios. Underline the specific terms / phrases used to answer question #3.
5. Which explanation is most likely correct given the evidence for Darwin’s and Lamarck’s theories?
DARWIN!