Loneliness is a complex and usually unpleasant emotional response to isolation. Loneliness typically includes anxious feelings about a lack of connectedness or communality with other beings, both in the present and extending into the future. As such, loneliness can be felt even when surrounded by other people. The causes of loneliness are varied and include social, mental, emotional, and spiritual factors. Research has shown that loneliness is widely prevalent throughout society among people in marriages, relationships, families and successful careers. It has been a long explored theme in the literature of human beings since classical antiquity. Loneliness has also been described as social pain — a psychological mechanism meant to alert an individual of isolation and motivate him/her to seek social connections. People can experience loneliness for many reasons and many life events may cause it, like the lack of friendship relations during childhood and adolescence, or the physical absence of meaningful people around a person. At the same time, loneliness may be a symptom of another social or psychological problem, such as chronic depression. Many people experience loneliness for the first time when they are left alone as infants. It is also a very common, though normally temporary, consequence of a breakup, divorce, or loss of any important long-term relationship. In these cases, it may stem both from the loss of a specific person and from the withdrawal from social circles caused by the event or the associated sadness. The loss of a significant person in one's life will typically initiate a grief response; in this situation, one might feel lonely, even while in the company of others. Loneliness may also occur after the birth of a child (often expressed in postpartum depression), after marriage, or following any other socially disruptive event, such as moving from one's home town into an unfamiliar community leading to homesickness. Loneliness can occur within unstable marriages or other close relationships in a similar nature, in which feelings present may include anger or resentment, or in which the feeling of love cannot be given or received. Loneliness may represent a dysfunction of communication, and can also result from places with low population densities in which there are comparatively few people to interact with. Loneliness can also be seen as a social phenomenon, capable of spreading like a disease. When one person in a group begins to feel lonely, this feeling can spread to others, increasing everybody's risk for feelings of loneliness. People can feel lonely even when they're surrounded by other people. A twin study found evidence that genetics account for approximately half of the measurable differences in loneliness among adults, which was similar to the heritability estimates found previously in children. These genes operate in a similar manner in males and females. The study found no common environmental contributions to adult loneliness.
 Emotional vs social isolation
One of the most popular typologies of loneliness was developed by Robert S. Weiss. He categorized loneliness into two types: Loneliness of Emotional Isolation (also known as emotional loneliness) and Loneliness of Social Isolation (also known as social loneliness). Emotional loneliness is derived from attachment theory. Part of attachment theory looks at the relationship between parents/caregivers and children. When securely attached children are separated from their parents, they exhibit separation distress such as crying, attempts to search for parents, and inhibited behavior. Adults get attached to romantic partners and show separation distress when separated from their partners. Weiss defined emotional loneliness as "separation distress without an object". This means that emotional loneliness is caused by the lack of a romantic partner, and feels like the separation...