Question

why are yawns contagious? we asked a scientist 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. use the passage to answer the question. what is the purpose of the transitions one theory and other proposals in this excerpt? (1 point) to group together explanations to the same question to draw a contrast between two ideas to show a cause/effect relationship to point out a specific example of a general phenomenon

Explanation:

The transitions "One theory" and "other proposals" are used to present different explanations for why yawning occurs. They group together various ideas related to the same question about the cause of yawning.

Answer:

to group together explanations to the same question