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A sibling is one of two or more individuals having one or both parents in common. A male sibling is called a brother, and a female sibling is called a sister. In most societies throughout the world, siblings usually grow up together, facilitating the development of strong emotional bonds such as love, hostility or thoughtfulness. The emotional bond between siblings is often complicated and is influenced by factors such as parental treatment, birth order, personality, and personal experiences outside the family.[1]


Little Julia tending the baby at home

Two siblings

Sibling is a modern revival of the Old English word sibling, meaning "relative, kinsman", a derivative of sibb "kinship, relationship", from Proto-Germanic *sibjō "race", from Proto-Indo-Europe mjbvkan *s(w)ebʰ- "one's own people, tribe". The term, along with its shortened form sib, may have been in use dialectally throughout the Middle English and Early Modern English periods, but was officially recognized c. 1903 when it came into common use in anthropology as a translation of the German Geschwister ("a brother or sister"). The word is further related to dialectal term sibred ("relationship"); as well as to the second part of the word gossip, from Old English gōdsibb, meaning "a sponsor, close relation".

Types of siblings

Full sibling

File:Full Siblings.PNG

A "full sibling" (full brother or full sister) is a sibling with whom an individual shares the same biological parents.


File:Half Siblings.PNG

Half-siblings only share one parent instead of two as full siblings do (i.e. the children that the parent and stepparent (i.e. mother and stepfather, or father and stepmother) have together). Half-siblings can have a wide variety of interpersonal relationships, from a bond as close as any full siblings, to total strangers.

There are specific terms for referring to half-siblings based on the sex of the shared parent:

  • Those that share the same mother (but different fathers) are known as a uterine sibling, or a maternal half-brother/sister.
  • Those that share the same father (but different mothers) are known as an agnate sibling, or a paternal half-brother/sister. In law, the term consanguine is used in place of agnate.

In 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.

3/4 sibling

Three-quarter siblings have one common parent, while their unshared parents have a mean consanguanuity of 50%. This includes full siblings and parent/child. (Similar terminology is used in horse breeding, where it occurs more frequently). Three-quarter siblings share more genes than half siblings, but fewer than full siblings. There are two genetic scenarios for 3/4 siblings:


In this case the unshared parents are full siblings. Further, the three-quarter siblings are also cousins. A possible example was the relationships between Queen Elizabeth I of England and both Henry Carey and Catherine Carey:

Elizabeth was the daughter of Henry VIII and Anne Boleyn. Henry Carey and Catherine Carey were children of Mary Boleyn, the sister of Anne Boleyn. Before Anne's marriage to King Henry, Mary was King Henry's mistress, and King Henry is believed by some to be the father of Henry Carey and Catherine Carey. If so, the two Careys would both be three-quarter siblings of Elizabeth.

A more recent example is that of Charles Lindbergh's children with his mistress Brigitte Hesshaimer, and his children with her sister, Marietta Hesshaimer. Another recent example relates to Jermaine and Randy Jackson, of the Jackson 5, who have both fathered children with Alejandra Genevieve Oaziaza.[2]

In the case where the unshared parents are identical twins, the children share as much genetic material as full siblings.

See also Deceased Wife's Sister's Marriage Act 1907.


In this case a woman has children with two men who are father and son (or the genders could be reversed). (This is not incest, as the woman is unrelated to the father and son.) These children will be three-quarter siblings.


A "stepsibling" (stepbrother or stepsister) is the child of one's stepparent from a previous or subsequent relationship. Not blood related.

Milk sibling

Milk brothers or sisters are children breastfed by either a woman who is the mother of one of the two babies, or by someone other than their biological mother, the latter a practice known as wetnursing and once widespread in the developed world, as it still is in parts of the developing world.

In Islam those who are fed in this way become siblings to the biological children of their wetnurse, provided that they are less than 2 years old. Islamic law (shariah) codifies the relationship between these people, and certain specified relatives, as rada'a; given that a child is breastfed five fulfilling (satisfactory to him) times, once they are adult, they are mahram, meaning that they are not allowed to marry each other, and the rules of modesty known as purdah are relaxed, as with other family members. But, laws of inheritance do not apply in the case of milk siblings.

Foster siblings

"Foster siblings" are children who are raised in the same foster home, or are also foster children of the person's parents, or foster parents' biological children.

Adoptive siblings

"Adoptive siblings" are when two children are legally related, but are not related by blood. Adopted siblings are not biologically related but may consider each other siblings because they act like they are.

  • Adoptive siblings that are adopted by the same legal mother and father are considered full adoptive siblings.
  • Adoptive siblings that are adopted by only the same legal mother are maternal adoptive half siblings.
  • Adoptive siblings that are adopted by only the same legal father are paternal adoptive half siblings.

Cross siblings

"Cross siblings" are not related in any way. Their only connection is that they share one or multiple half-siblings. For example, in The Young and the Restless, Michael is the maternal half sibling of Kevin, and the paternal half sibling of Eden. In this case, Kevin and Eden are cross siblings - they share no blood. Not to be confused with stepsiblings. In Desperate Housewives, M.J. Delfino is the half brother of Julie Mayer and Julie is the half sister of Evan Mayer so M.J. and Evan are cross siblings related in any way.

Sibling cousins

"Sibling cousins" are those who have the same mother with their fathers being brothers or cousins or who share the same father with their mothers being sisters or cousins. This is a broader category than, but inclusive of, the 3/4 sibling above.

Birth order

P S Krøyer 1897 - Døtrene Benzon

The Benzon Daughters by Peder Severin Krøyer.

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 are 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.[3][4] 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.[5]

Some research has found that firstborn children have slightly higher IQs on average than later born children.[6] However, other research finds no such effect.[7]

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.

Regressive behavior at the birth of a new sibling

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.

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

Sir Joshua Reynolds 004

Portrait of Lady Cockburn and her Three Eldest Sons, by Joshua Reynolds.

"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 or of the same gender.[8] 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.[9] Children are sensitive from the age of 1 year to differences in parental treatment and by 3 years they have a sophisticated grasp of family rules and can evaluate themselves in relation to their siblings.[1] Sibling rivalry often continues throughout childhood and can be very frustrating and stressful to parents.[10] One study found that the age group 10–15 reported the highest level of competition between siblings.[11] 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% of siblings over age 60 enjoy close ties.[1]

Each child in a family competes to define who they are as persons 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.[10] 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.[12] 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.[11]

Westermarck effect and its opposite

Anthropologist Edvard Westermarck found that children who are brought up together as siblings are desensitized to form sexual attraction to one another later in life. This is known as the Westermarck Effect. It can be seen in biological and adoptive families, but also in other situations where children are brought up in close contact, such as the Israeli kibbutz system and the Chinese Shim-pua marriage.[13][14]

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.

Famous sibling groups

William-Adolphe Bouguereau (1825-1905) - Two Sisters (1901)

Two Sisters by William-Adolphe Bouguereau.


Brothers Prince Edward V of England and Prince Richard of Shrewsbury, 1st Duke of York.

Painting of Brontë sisters

The Brontë sisters, painted by their brother

The Mario Brothers


See also


  1. ^ a b c Mersky Leder, Jane (Jan/Feb 1993). "Adult Sibling Rivalry". Psychology Today. Retrieved November 28, 2006. 
  2. ^
  3. ^ Ernst, C. & Angst, J. (1983). Birth order: Its influence on personality. Springer.
  4. ^ Jefferson, T., Herbst, J.H., & McCrae, R.R. (1998). Associations between birth order and personality traits: Evidence from self-reports and observer ratings. Journal of Research in Personality, 32, 498–509.
  5. ^ Harris, J.R. (1998). The Nurture Assumption: Why children turn out the way they do. New York: Free Press.
  6. ^ Carey, Benedict (June 21, 2007). "Family dynamics, not biology, behind higher IQ". International Herald Tribune. Retrieved July 15, 2007. 
  7. ^ Rodgers, J.L., Cleveland, H.H., van den Oord, E. and Rowe, D. (2000). Resolving the Debate Over Birth Order, Family Size and Intelligence. American Psychologist, Vol. 55.
  8. ^ The Effects of Sibling Competition Syliva B. Rimm, Educational Assessment Service, 2002.
  9. ^ New Baby Sibling University of Michigan Health System, June 2006
  10. ^ a b Sibling Rivalry University of Michigan Health System, October 2006
  11. ^ a b Sibling Rivalry in Degree and Dimensions Across the Lifespan Annie McNerney and Joy Usner, 30 April 2001.
  12. ^ Freud Lecture: Juliet Mitchell, 2003
  13. ^ Westermarck, E.A. (1921). The history of human marriage, 5th edn. London: Macmillan, 1921.
  14. ^ Arthur P. Wolf. "Childhood Association and Sexual Attraction: A Further Test of the Westermarck Hypothesis". American Anthropologist, New Series, Vol. 72, No. 3 (Jun. 1970). pp. 503–515. Retrieved November 29, 2006. 

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This page uses content from the English language Wikipedia. The original content was at Sibling. The list of authors can be seen in the page history. As with this Familypedia wiki, the content of Wikipedia is available under the Creative Commons License.

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