Sibling
A sibling shares at least one biological parent.
A sibling is a relative that shares at least one parent with another person. Male siblings are brothers, female siblings are sisters, and a person with no siblings is an only child. Siblinghood is considered a unique type of relationship, often characterized by strong emotional bonds that develop from growing up together, though these bonds can be complicated by factors such as parental treatment, birth order, personality, and personal experiences outside the family.
- definition
- Relative sharing at least one parent
- types
- Full-sibling, half-sibling, three-quarter sibling, dibling
- genetic relatedness (full-sibling)
- 50% consanguinity (first-degree relative)
- genetic relatedness (half-sibling)
- 25% consanguinity (second-degree relative)
- common type
- Full-siblings
Lore & Background
Full-siblings share both biological parents and are the most common type of siblings. Twins are siblings born from the same pregnancy and generally share a greater bond due to growing up together and being the same age. Half-siblings share one parent and may be uterine (same mother) or agnate (same father). In law, half-siblings have often received unequal treatment compared to full-siblings, such as in old English common law where half-siblings took only half as much property in intestate succession; this inequality has been abolished in England but still exists in Florida.
Reader's Guide
Siblings represent a fundamental human relationship, with genetic relatedness forming a basis for legal and social bonds. Medically, full-siblings are first-degree relatives (50% related), while half-siblings are second-degree relatives (25% related). However, actual DNA sharing varies: full siblings share on average 50.28% of their DNA with a standard deviation of 3.68%, meaning about one-quarter of sibling pairs share more than 52.76% and one-quarter share less than 47.8%. Three-quarter siblings, who share one parent while the unshared parents are first-degree relatives (e.g., siblings or parent-child), are genetically closer than half-siblings but less close than full-siblings, though this is rare in humans. The concept of siblings extends beyond blood relations to include stepsiblings, adoptive siblings, foster siblings, and diblings (donor-conceived siblings). Birth order—typically classified as eldest, middle child, or youngest—is a key factor studied in sibling dynamics.
Did You Know?
- Full-siblings share 50% consanguinity and are first-degree relatives, while half-siblings share 25% and are second-degree relatives.
- Three-quarter siblings, such as those in Charles Lindbergh's family, share one parent while the unshared parents are first-degree relatives.
- In old English common law, half-siblings took only half as much property of their intestate siblings' estates as full-siblings; this inequality still exists in Florida.
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