Anthropologists categorize laws of descent under four broad areas. There are four types of descent: bilateral, unilineal, ambilineal, and double descent. Bilateral descent, also known as two-sided descent, connects a person to relatives on both his father's and mother's sides. Everyone else is considered unconnected to them. Under this system, every relative is equally important, with no one more significant than another.
In unilineal descent, also called single-handed descent, people get married within their clan or family and then only those families will be connected through marriage. The others remain unconnected. This method leaves no room for inheritance; everything is passed on to your children either by being raised in the house or through gifts. So only people who have children can practice unilineal descent.
In ambilineal descent, also called middle-handed descent, individuals choose which side they want to follow based on what role they think it will play in their lives. People on the same ambilineal path will sometimes marry each other to keep the lines of communication open. However many times they may not know this until after they choose their own paths.
Double descent is when someone takes siblings as partners in crime. They work together to take care of their parents while trying to make it on their own in the world. Double descent families usually live close by each other so they can take care of each other when needed.
Descent is supreme. If you find that you are connected to people on both sides of your family, this type of descent is present in your pedigree. All humans can be classified as being either descended from males or females; therefore, all humans are bilateral descendants.
Unilineal descent is when one side of the family tree is more important than the other. This can happen if there was a death in the family, for example, or if one branch of the family did not have contact with others. In this case, descent would only go through the living members of the family who carry this unilineal descent.
Ambilineal descent is when both lines of the family tree are equal in importance. This can also happen if there were deaths in the family, or if one line didn't have contact with others. In this case, descent would go through the living members of the family who carry this ambilineal descent as well as the deceased members of the family.
Double descent occurs when two families share a common ancestor. This could be someone who had multiple children or married into the family.
Bilateral descent is a family lineage system in which relatives on both the mother's and father's sides are equally essential for emotional bonds or the transmission of property or riches. It's a family arrangement in which descent and inheritance are distributed equally between both parents. In contrast, unilateral descent is when one parent is primarily responsible for passing down their genes while the other has little influence over how they are inherited.
In ancient times, most families were expected to follow a bilateral system of descent, but today this is not the case for many reasons including marriage equality and single parenting families. Even so, some studies have shown that men prefer women with bilateral descent lines while women prefer men with unilateral descent lines. This may explain why you see more wealthy people with bilateral descent and less wealthy people with unilateral descent.
There are two types of bilateral descent: open and closed. With an open system, anyone can marry into the family, changing its descent status from unilateral to bilateral. With a closed system, only persons in certain positions can marry into the family, ensuring that it remains with a specific group. For example, in the English aristocracy, males could become members of the family by inheriting it, but females could not. Instead, they would need to be granted membership by an older member of the family called a "lord" or "lady".
A bilateral descent pattern is followed by 60% of cultures, the majority of which are developed nations. Unilateral descent (tracing kinship through just one parent) is practiced in the remaining 40% of the world's communities, with a significant concentration in pastoral cultures (O'Neal 2006).
The distribution of descent groups across societies provides evidence for the role of selection in shaping genetic diversity within populations (Boyd and Richerson 1985). The prevalence of particular descent patterns can also be used to infer the importance of certain traits that determine who will be born into what family. For example, among the!Kung, women choose their husbands, which means that they can refuse marriage proposals or leave bad relationships. This ability to break free from restrictive social norms has allowed some women to escape from poverty and oppression. Among the Iroquois, by contrast, men choose their wives, which means that if a woman does not like her husband's choice, they can divorce him or her. Divorce was therefore rarely required by the Iroquois culture, which tended to favor agreement over conflict.
In conclusion, bilateral descent is common because it allows for new families to be created when two previously unconnected people come together. This is important for individuals to have healthy relationships and for populations to increase their genetic diversity.