In 1938, scientists found a population of coelacanths in the Indian Ocean. This fish species is considered a “living fossil” and appears not to have changed morphologically for 80 million years. This discovery supports the ___________ model of evolution.

Question

A.  gradualism
B.  punctuated equilibrium
C.  adaptation
D.  natural selection
E.  common descent

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?

  Gather Content
· What do you already know about punctuated equilibrium?

  Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?

  Reflect on Process · Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

B.  punctuated equilibrium

Clarify Question
· What is the key concept addressed by the question?
        o This question addresses punctuated equilibrium.
· What type of thinking is required?
        o This question is asking you to take what you already know and apply it to this unfamiliar situation.

  Gather Content
· What do you already know about punctuated equilibrium?
        o The punctuated equilibrium hypothesis argues that species have long periods of little or no evolutionary change (termed stasis), punctuated by quick bursts of evolutionary change.
        o When natural selection is strong, evolutionary change can occur rapidly, so the “punctuated” part of the theory is not controversial. A more difficult question involves the long periods of stasis (the equilibrium): Why would species exist for thousands, or even millions, of years without changing?
        o Most researchers now believe that a combination of stabilizing and oscillating selection is responsible for stasis. If the environment does not change over long periods of time, or if environmental changes oscillate back and forth, then stasis may occur for long periods.

  Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o The unusual thing about the coelacanth is that it appears to have not changed over a long time. This is an example of stasis.
        o Of the listed options, the one that predicts that species will sometimes stay the same is punctuated equilibrium.
        o Punctuated equilibrium predicts that species may stay unchanged for long periods of time, then undergo bursts of rapid change.

  Reflect on Process · Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o The question required you to take what you already know and apply it to this unfamiliar situation.
        o Did you recognize that the coelacanth is an example of a species in stasis, which is a prediction of punctuated equilibrium?