Scientists observed that marine bryozoan fossils lack intermediate forms. This evidence supports which hypotheses? Check all that apply.A) Evolution occurs in spurts, alternating with long periods of little change.B) Evolution proceeds steadily, with gradual, incremental change in a given evolutionary line.C) There is variability in the rate of evolution.D) Evolution proceeds at a constant rate that is the same for all organisms.

Question

What will be an ideal response?

Answer 1

A, C

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 analyze the information given, using logic, to dissect the problem and determine the answer.

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 Does the lack of intermediate fossils suggest that evolution proceeds steadily? No, because then you would expect to see the gradual change reflected in the fossil record.
        o Does the lack of intermediate fossils suggest that evolution proceeds at a constant rate that is the same for all organisms? No, because you would expect to see intermediate fossils represented.
        o Does the lack of intermediate fossils suggest that there is variability in the rate of evolution? Yes. Infrequent, rapid change means that intermediate forms may not become fossilized.
        o Does the lack of intermediate fossils suggest that evolution occurs in spurts, alternating with long periods of little change? Yes. This can explain why intermediate forms were not well-represented in the fossil record.

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 analyze the information given, using logic, to dissect the problem and determine the answer.
        o Did you recognize that a lack of intermediate fossils suggests that change happens quickly, in keeping with the punctuated equilibrium model?