Descent Principles: Part 2

Bilateral click this icon to hear the preceding term pronounced, descent is used by most people in Europe and the Americas today.  This cognatic system traces descent from all biological ancestors regardless of their gender and side of the family.  In addition, all male and female children are members of both their father's and mother's families.  Everyone shown in red below is a bilateral relative of ego.

Diagram of bilateral descent

In some societies that use bilateral descent, the non-red people in the diagram may also be considered relatives.  However, this is often a matter of individual choice.  In North America, they are referred to as in-laws and are generally considered to be more distant kinsmen.  Take another look at the diagram above and think about who you consider to be your relatives.  Does your family follow this or one of the other descent patterns described in the last section of the tutorial?

While there is no inherent gender bias in the bilateral descent principle, there often is a slight male bias in marriage practices and in the creation of families.  This can be seen in North America today when a man's last name is used by his wife and children.  With this exception, however, there usually is no other similarity with patrilineal descent.

Bilateral descent is rare among the societies of the world, though, it is common if you count people instead of societies.  It is characteristic of large agricultural and industrial nations as well as hunters and gatherers in harsh, relatively nonproductive environments such as deserts and arctic wastelands.  It is also found among some transhumance click this icon to hear the preceding term pronounced pastoralists living in poor environments.

How Many Relatives do you have?

The specific type of descent system employed has a major effect on the number of people who are recognized as ancestors.  With unilineal descent, there is only one direct ancestor in each generation.  However, with bilateral descent, there is a doubling of ancestors with each generation further back in time.

Unilineal Bilineal Bilateral
1 1 2  2
2 1 2  4
3 1 2  8
4 1 2 16
5 1 2 32
6 1 2 64

Given the fact that bilateral descent results in many ancestors in just a few generations, it is not surprising that few people in North America know the names of all eight of their great grandparents, let alone the names of their sixteen great great grandparents.

Photo of a large bilateral kindred in North America gathered together for a wedding

A large bilateral family in North America


By comparison, it is not unusual for people who use unilineal descent systems to remember all of their ancestors for five or more generations.  In fact, some Polynesians from the island of Rarotonga in the early 20th century knew the names of their ancestors back 90 or more generations.  In fairness, however, it should be noted that the people of Rarotonga traditionally have had more of an ancestor focus than do most people in North America today.  This difference in focus may have as much to do with their respective economies and pace of life as with their kinship systems.

One further trait of bilateral descent deserves mention.  Families using this system have a potential for recognizing far more collateral pronounce the word descendants than would those using one of the unilineal patterns.  This is not due to producing more offspring but to having descent lines continued by both male and female children every generation.


You have learned that the two principle ways people around the world trace descent are unilineal and cognatic (or nonlineal).  Unilineal descent recognizes only a single line of ancestors through males or females.  It occurs in two forms--patrilineal, which follows the male line, and matrilineal, which follows the female line.  The patrilineal form is more common.  With cognatic descent, both the mother's and the father's ancestors to some degree are considered to be within the family line.  Cognatic descent occurs in four forms--bilineal, parallel, ambilineal, and bilateral descent.

  unilineal descent    patrilineal descent   
   matrilinal descent
  cognatic descent    bilineal descent 
   parallel descent
   ambilineal descent
   bilateral descent

One final caution is in order.  People do not always follow their culture's descent principles precisely.  Kinship is often manipulated.   For instance, people may create or deny links to particular ancestors in order to make their genealogy come out to their advantage.  In addition, kinship systems are changing rapidly today as societies are increasingly exposed to other cultures around the world and new kinds of economies.


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This page was last updated on Friday, March 16, 2007.
Copyright 1997-2007 by Dennis O'Neil. All rights reserved.
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