The Science of Yawning

The Science of Yawning
Have you yawned today? If you can't remember or perhaps haven't noticed, you're similar to most Americans. According to a 2007 study, yawning is considered a basic bodily function, such as scratching an itch or crossing one's legs, and people hardly make note of the act. Despite its normality in our daily routines, the question regarding why yawning occurs still has not been answered with certainty. Interestingly enough, little research has been paid to studying yawning, due to a debate surrounding its importance. Many scientists disagree on the importance surrounding research for yawning. Those against the research believe that it will not greatly impact the scientific and medicinal communities, while others believe that there is a case to be made for the possible physiological significance of a somewhat pointless act.
There are a few possible causes as to why one yawns, and even fewer theories related to the evolutionary reason for yawning. The most established theory is that yawning helps a person increase his or hers state of alertness. This is one reason as to why yawning has been associated with sleepiness, or when a person is extremely fatigued. In fact, one famous study has suggested that yawning may have developed as a way of keeping animals alert to possible predators. This gives way to the "contagious" yawn theory, which involves an instinctual reaction to warn another member of the "herd" to stay alert in times of danger. These evolutionary theories are also connected to theories regarding empathy. Various studies have shown that spatial proximity in socially close primates is an indicator of yawn contagion.
Other scientists believe that yawning is a sign of the body regulating its temperature and cooling itself down. Neuroscientists have attributed yawning to another possible theory regarding the neurotransmitters in the brain. They believe that chemicals responsible for yawning, including serotonin and dopamine, also cause feelings such as hunger and happiness. Thus, as more of these compounds are activated in the brain, the more frequently a person yawns. In one psychological study on the effects of antidepressant medication, researchers found that people undergoing withdrawal from opioids and those taking serotonin reuptake inhibitors (SSRIs) yawned more often than the people in the control group. This can give way to the idea that chemicals in the brain-especially serotonin-can have an impact on the frequency of yawning.
Yawning continues to be an interesting phenomenon with a plethora of possible causes. Theories ranging from chemical balances to empathy relation are all within the realms of possible reasons as to why people yawn, but scientists will most likely study these theories for decades to come. Until a conclusive, definitive answer is reached, it may be safe to assume that yawning acts as a diverse linguistic signal that can represent various functional outcomes.
Which of the following statements rephrases the author's main argument about the cause of yawning?

A) Yawning is a sign of the body cooling itself down.
B) While scientists are still not aware why people yawn, one can safely assume that it is linked to a linguistic signal.
C) There are many different possible causes, but theories regarding chemical balances are the most promising.
D) Most people are not even aware of how many times they yawn per day.