A sibling is a brother or sister; that is, one who shares the same parents.
In most societies throughout the world, siblings usually grow up together and spend a good deal of their childhood with each other. This genetic and physical closeness may be marked by the development of strong emotional associations such as love or enmity. The sibling bond is often complicated and is influenced by factors such as parental treatment, birth order, personality, and people and experiences outside the family.
At law (and especially inheritance law) half siblings were often accorded unequal treatment. Old English common law at one time incorporated inequalities into the laws of intestate succession, with half siblings taking only half as much property of their intestate siblings' estates as other siblings of full-blood. Unequal treatment of this type has been wholly abolished in England and throughout the United States.
In Islam those who are fed in this way become siblings to the biological children of their wetnurse, provided that they are less than two years old and have been breastfed five times or more by her. Islamic law (shariah) codifies the relationship between these people, and certain specified relatives, as rada; once they are adult, they are mahram, meaning that they are not allowed to marry each other, and the rules of modesty known as hijab are relaxed, as with other family members.
Birth order is a person's rank by age among his or her siblings. Typically, researchers classify siblings as “eldest”, “middle child”, and “youngest” or simply distinguish between “firstborn” and “later born” children.
Birth order is commonly believed in pop psychology and popular culture to have a profound and lasting effect on psychological development and personality. For example, firstborns are seen as conservative and high achieving, middle children as natural mediators, and youngest children as charming and outgoing. In his book Born to Rebel, Frank Sulloway argues that firstborns to be more conscientious, more socially dominant, less agreeable, and less open to new ideas compared to laterborns. Literature reviews that have examined many studies and attempted to control for confounding variables tend to find minimal effects for birth order on personality. In her review of the scientific literature, Judith Rich Harris suggests that birth order effects may exist within the context of the family of origin, but that they are not enduring aspects of personality.
Some research has found that firstborn children have slightly higher IQs on average than later born children. However, other research finds no such effect.
In practice, systematic birth order research is a challenge because it is difficult to control for all of the variables that are statistically related to birth order. For example, large families are generally lower in socioeconomic status than small families, so third born children are more likely than firstborn children to come from poorer families. Spacing of children, parenting style, and gender are additional variables to consider.
The arrival of a new baby is especially stressful for firstborns and for siblings between 3 and 5 years old. Regressive behavior and aggressive behavior, such as handling the baby roughly, can also occur. All of these symptoms are considered to be typical and developmentally appropriate for children between the ages of 3-5. While some can be prevented, the remainder can be improved within a few months. Regressive behavior may include demand for a bottle, thumb sucking, requests to wear diapers (even if toilet-trained), or requests to carry a security blanket.
Regressive behaviors are the child’s way of demanding the parents’ love and attention. Parents can deal with these behaviors by explaining to the older child their new sibling role, making this role sound exciting, answering questions about the baby and the process of birth (as appropriate), or reserving time each day just for the parent and older child.
The American Academy of Pediatrics suggests that instead of protesting or telling children to act their age, parents should simply grant their requests without becoming upset. The affected children will soon return to their normal routine when they realize that they now have just as important a place in the family as the new sibling. Most of the behaviors can be improved within a few months.
The University of Michigan Health System advises that most occurrences of regressive behavior are mild and to be expected; however, it recommends parents to contact a pediatrician or child psychologist if the older child tries to hurt the baby, if regressive behavior does not improve within 2 or 3 months, or if the parents have other questions or concerns.
Sibling rivalry is a type of competition or animosity among brothers and sisters. It appears to be particularly intense when children are very close in age and of the same gender. Sibling rivalry can involve aggression; however, it is not the same as sibling abuse where one child victimizes another.
Sibling rivalry usually starts right after, or before, the arrival of the second child. While siblings will still love each other, it is not uncommon for them to bicker and be malicious to each other. Children are sensitive from the age of one year to differences in parental treatment and by three years they have a sophisticated grasp of family rules and can evaluate themselves in relation to their siblings. Sibling rivalry often continues throughout childhood and can be very frustrating and stressful to parents. One study found that the age group 10 to 15 reported the highest level of competition between siblings Sibling rivalry can continue into adulthood and sibling relationships can change dramatically over the years. Approximately one-third of adults describe their relationship with siblings as rivalrous or distant. However, rivalry often lessens over time and at least 80 percent of siblings over age 60 enjoy close ties.
According to researchers, each child in a family competes to define who they are as individuals and want to show that they are separate from their siblings. Sibling rivalry increases when children feel they are getting unequal amounts of their parents’ attention, where there is stress in the parents’ and children’s lives, and where fighting is accepted by the family as a way to resolve conflicts. Sigmund Freud saw the sibling relationship as an extension of the Oedipus complex, where brothers were in competition for their mother's attention and sisters for their father's. Evolutionary psychologists explain sibling rivalry in terms of parental investment and kin selection: a parent is inclined to spread resources equally among all children in the family, but a child wants most of the resources for him or herself.
The opposite phenomenon, when relatives do fall in love, is known as genetic sexual attraction. This can occur between siblings brought up apart from each other, for example, adoptees who are re-united in adulthood.