A family is a group of people who, in most cases, live together. They share their money and food and are supposed to take care of one another. Its members are either genetically related (like brother and sister) or legally bound to each other, for example by marriage. In many cultures, the members of a family have the same or a similar surname.
A family is said to be society's smallest unit, its nucleus. Family life is more private and intimate than public life. But in most countries there are laws for it. For example, there are restrictions for marrying within the family and bans for having a sexual relationship with relatives, especially with children.
Types of families[change | change source]
Three types of family are: nuclear family, single-parent family and extended family.
- A nuclear family is made up of parents and one or more children living together.
- A single-parent family is one where there is one parent and one or more children.
- An extended family or joint families means father, mother, daughters, sons, grandparents, uncles, aunts, cousins, nieces and nephews. In many countries including China, Pakistan and India, extended or joint families traditionally live together.
Both the "nuclear family" and the "single-parent family" are also called the "immediate family".
Foster families are families where a child lives with and is cared for by people who are not his or her parents.
Closeness[change | change source]
Some family members are genetically closer to each other. The following table gives examples:
|Inbred strain||not applicable||99%|
|Identical twins||not applicable||100%|
|Full sibling||first-degree||50% (2−2+2−2)|
|3/4 siblings or sibling-cousin||second-degree||37.5% (2−2+2⋅2−4)|
|Half-aunt, half-uncle||third-degree||12.5% (2⋅2−4)|
|Great grandparent||third-degree||12.5% (2−3)|
|First cousin||fourth-degree||12.5% (2⋅2−4)|
|Double first couisin||fourth-degree||25% (2−3+2−3)|
|Half-first cousin||fourth-degree||6.25% (2−4)|
|First cousin once removed||fifth-degree||6.25% (2⋅2−5)|
|Second cousin||sixth-degree||3.125% 3.13% (2−6+2−6)|
|Double second cousin||sixth-degree||6.25% (4⋅2−6)|
|Triple second cousin||sixth-degree||12.5% (8⋅2−6)|
|Quadruple second cousin||sixth-degree||9.38% (6⋅2−6)|
|Third cousin||seventh-degree||0.781% (2⋅2−8)|
|Fourth cousin||tenth-degree||0.20% (2⋅2−10)|
- By replacement in the definition of the notion of "generation" by meiosis". Since identical twins are not separated by meiosis, there are no "generations" between them, hence n=0 and r=1. See genetic-genealogy.co.uk.
- "Kin Selection". Benjamin/Cummings. Retrieved 2007-11-25.
- This degree of relationship is usually indistinguishable from the relationship to a random individual within the same population (tribe, country, ethnic group).