What statement best summarizes the evolutionary history of eyes?

Question

A.  Development of light-sensing organs evolved once, but several eye structures evolved separately.
B.  Eyes evolved once and were slightly modified in different phyla.
C.  Eyes evolved separately in each phylum from an ancestor with no ability to detect light.
D.  Light-detection organs can develop with very little developmental constraint.

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 eyes? What other information is related to the question?

Choose Answer
Given what you now know, what information 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

A.  Development of light-sensing organs evolved once, but several eye structures evolved separately.

Clarify Question
What is the key concept addressed by the question?
        · How did eyes evolve?
What type of thinking is required?
            o This is an evaluate question because you have to weigh and judge the different means by which eyes could have evolved.

Gather Content
What do you already know about eyes? What other information is related to the question?
        · You already know that the structure of animal eyes differ by group. For example, insects have eyes with multiple lenses while vertebrates only have one. You also know that all eyes have to be able to detect light by means of photoreceptors, and that even the simplest eyes, like the eyespots of some invertebrates like flatworms, contain photoreceptor cells.

Choose Answer
Given what you now know, what information is most likely to produce the correct answer?
        · The statement that the development of light-sensing organs evolved once, but several eye structures evolved separately makes the most sense in terms of evolution and what you know about the features of eyes in different animal taxa. The statement that eyes were only slightly modified in different taxa is false since eyes can be very different in flatworms, flies, and vertebrates. The statement that modern animal eyes evolved from an ancestor that had no ability to detect light is not true as even simple organisms like flatworms can detect light, although some organisms have secondarily lost the ability to see (such as cavefishes).

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 Answering this question correctly depended upon your ability to weigh or judge the proper process of evolution of the eye. If you chose an incorrect answer, where did you go wrong? Did you think that light-detection organs can develop with very little developmental constraints? Some genes that control eye development are similar across taxa (like Pax6), showing that development is constrained by similar processes across taxa. Also there are physical constraints on how an eye can develop in order to produce a focused image upon a set of photoreceptor cells. Did you think that eyes only evolved once? It is true that it is thought that light-detection evolved once, but that different types of eyes evolved separately.