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Cousin

society Maturity 11-13 Next article →

A cousin is a relative who shares a common ancestor but is not a sibling, parent, or child. In the kinship system used in English-speaking countries, the term "cousin" is a broad category. It includes many different types of relationships based on how many generations separate people from their shared ancestor. Because this single word covers so many different links, an individual can have many more cousins than any other type of relative. Genealogists, who study family histories, can sometimes track hundreds of these relationships across several centuries.

To describe these relationships precisely, people use the terms "degree" and "removal." The degree measures how many generations exist between the cousins and their most recent common ancestor. For example, a first cousin is one degree away from that ancestor. The degree is calculated by looking at the cousin closest to the ancestor and subtracting one. Removal describes the difference in generations between the two cousins. If two cousins belong to different generations, they are "removed." For instance, a first cousin once removed is one generation apart. Two people might be removed but still be close in age if their parents had children at very different times.

There are many specific ways to categorize these relatives. A maternal cousin is related through a mother, while a paternal cousin is related through a father. These relationships are not always reciprocal. One person's maternal cousin might be the other person's paternal cousin. We also use the terms "parallel" and "cross" cousins to describe how they are related. Parallel cousins descend from same-sex siblings. Cross cousins descend from opposite-sex siblings. Some families also use terms like "cousin-uncle" or "cousin-niece" to show if a cousin belongs to an older or younger generation.

Some cousins are more closely related than others due to unique family connections. Double first cousins occur when two siblings from one family marry two siblings from another family. These cousins share both sets of grandparents, making them "doubly related." In contrast, half cousins share only one grandparent because they are descended from half-siblings. There are also step-cousins, who are related through marriage rather than blood. A step-cousin might be the child of a parent's step-sibling or the stepchild of an aunt or uncle.

Scientists use the term consanguinity to measure how closely individuals are related by blood. This is often expressed as a coefficient of relationship. A coefficient of one represents a person's relationship to themselves. For first cousins, the consanguinity is one-eighth. This value decreases as the degree or removal increases. If cousins are half cousins, their consanguinity is half that of ordinary cousins because they share only one ancestor. Interestingly, double first cousins have a consanguinity equal to that of half-siblings. If identical twins both have children with another pair of identical twins, the resulting double cousins are as genetically similar as siblings.

Cousin marriage is a practice that has appeared throughout history and in many different cultures. Historically, as many as 80 percent of all marriages were between first or second cousins. Today, about 10 percent of marriages fall into this category. In some regions, such as the Middle East, more than half of all marriages are between first or second cousins. Anthropologists believe these marriages are sometimes used to strengthen families, conserve wealth, or protect cultural heritage. While some cultures encourage these unions, others attach a strong social stigma to them.

There are biological factors involved in close kinship. When couples are closely related, there is an increased chance of sharing certain genes, including recessive mutations. If both parents share a recessive mutation, it may be revealed in their children, increasing the risk of recessive genetic disorders. However, some research shows a different side to this. A study in Iceland found that couples related as third cousins had the greatest reproductive success. This may be because closer kinship can sometimes decrease the likelihood of immunological incompatibility during pregnancy. Over many generations, however, sustained cousin marriage within a population can lead to increased genetic disorders across the entire group.

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File:Victoria and her cousin, 1852.jpg
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