"Why Are Yawns Contagious? We Asked a Scientist"

Question

by Teresa Carey

There is no scientific consensus on why we yawn.

One theory argues that when humans are tired, we stop taking deep breaths, which causes a build-up of carbon dioxide in the body, said Douglas Parham, a speech scientist at Wichita State University. A yawn might be a special kind of respiration, Parham said. It builds up oxygen quickly, while expelling carbon dioxide, even more than a deep breath.

Excess carbon dioxide and other chemical changes, such as a drop in oxygen or increase in a compound called adenosine, could also act as “yawn gates,” said James Giordano, a neuroethicist and neuroscientist at Georgetown University. These chemicals send out a signal that triggers a yawn. By yawning, we compress the muscles of the face, driving oxygen-enriched blood to the brain, Giordano said.

Other proposals state the purpose of yawning is to cool the brain, or to stretch internal organs like tissues and lungs, helping the body to liven up.

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Question
Use the passage to answer the question.

What is the purpose of the transitions “One theory” and “other proposals” in this excerpt?

(1 point)
Responses

to draw a contrast between two ideas
to draw a contrast between two ideas

to point out a specific example of a general phenomenon
to point out a specific example of a general phenomenon

to show a cause/effect relationship
to show a cause/effect relationship

to group together explanations to the same question
to group together explanations to the same question

Answer 1

The purpose of the transitions “One theory” and “other proposals” in this excerpt is to group together explanations to the same question.