Still Trying to Explain ...
29. The hanging ball at the back of your throat.
Scientists don’t understand exactly what the uvula does, but because it is largely unique to humans, they suspect it plays a role in speech, possibly secreting enough saliva to lubricate the mouth while speaking and swallowing. You may not need a uvula to speak English. But for speakers of languages such as French and Arabic that use sounds known as uvular consonants (the r in the French word maître, for example), a missing uvula may alter their speech.
30. Hypnic jerks.
An estimated 70 percent of people have felt a sudden jerk right before they fall into a deep sleep. Research hasn’t pinpointed the reason behind these socalled hypnic jerks, but one theory is that as your breathing and heart rate slow down, your muscles start to relax and may twitch. It could also be that the brain sends a signal to your muscles to tense up because it misinterprets their relaxation as a sign that you’re falling.
31. “Old-people smell.”
A small study from 2012 confirmed that older people have a less intense scent (some call it musty or grassy) than young and middle-aged folk. It’s not clear what causes this shift in odor as we get older, but researchers speculate that it might be due to a type of white blood cell supply that increases as we age.
32. Different blood types.
Scientists aren’t sure why humans have different blood types. There does appear to be an association between blood types and certain diseases. For example, people with blood type A are at a higher risk for some forms of stomach and pancreatic cancer compared with people with blood type O, who are more likely to have ulcers and ruptured Achilles tendons.
33. Random eyelid twitching.
A twitchy eyelid can last anywhere from minutes to days. Most of these twitches are harmless and don’t affect your vision. “We don’t know why this happens exactly, but fatigue, caffeine, and stress are common culprits,” says Dr. Rantala. Try applying a warm compress to your twitchy eye and gently massaging the lid with your fingers to relax the muscles.
34. Yawning.
While there’s no shortage of theories, the true reasons for yawning remain a mystery. One theory suggests that the deep inhalation and short exhalation of a yawn increase blood flow to the brain, cooling it down. Another explanation is that a yawn gives your body a jolt, since your heart rate increases and your eye muscles tense up after you yawn.
35. Handedness.
Other animals, including polar bears and chimpanzees, also have handedness, but those species are split 50/50 between right and left. Humans are the only ones that show a distinct bias as a species toward one hand (90 percent of us are right-handed), and scientists have no idea why.
36. The appendix.
Charles Darwin theorized that the appendix was the useless evolutionary remains of a larger structure that housed bacteria our plant-eating ancestors needed to digest stubborn plant tissues such as tree bark. Modern scientists aren’t convinced. Some think that the tubelike organ actually promotes the growth of some kinds of good gut bacteria.
37. Fingerprints.
Our fingerprints are unique, though they do come in a few broad patterns: loops, whorls, and arches. Researchers have found that some patterns are associated with certain diseases—people with loop prints have a higher incidence of bronchial asthma and dementia, for instance. What we don’t know is why fingers have these swirly patterns in the first place. For many years, scientists thought they helped us grip things, but fingerprints actually allow less of our skin to come into contact with objects. Another theory: They somehow protect our fingers or provide touch sensitivity.
38. The mesentery.
In November 2016, researchers officially added another organ to anatomy textbooks. Scientists used to think the mesentery was a few unconnected sections of tissue scattered in the intestines. But after peeling back layers of the gut, they now realize it’s a single organ: a double fold of membrane in the digestive system that holds up the intestines; connects them to the abdomen; and has a distinct, twofoot-long structure that spreads out like a Chinese fan. Its function? They still aren’t sure.