Some common human behaviors include crying, hiccuping, sleeping, blushing and laughing. Some of these common human behaviors appear to serve no real purpose, while others have explanations rooted in science. Crying, for example, happens due to intense or stressful emotions. Scientists think that the tears may contain undesirable elements produced by the body during times of stress.
Hiccups are involuntary muscle spasms involving the diaphragm, however, scientists do not really know what purpose they serve or why exactly they happen. Sometimes they are associated with too much or too little food. Humans spend about one third of their lives asleep, and going without sleep leads to a breakdown of mental and physical abilities. However, scientists do not fully understand why sleep is necessary.
Blushing is another universal human behavior that happens in various instances of social interaction. It can be a sign of embarrassment or simply receiving unwanted or unexpected attention. It causes veins in the to face dilate, which allows more blood in. Scientists also do not understand why blushing happens.
Laughing is a common human response to something funny. It typically has a positive effect on both the person laughing and those around them. Besides humans, apes and monkeys also tend to laugh and grin during play or social situations.