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In
genealogy Genealogy (from el, γενεαλογία ' "study of family trees") is the study of families In human society, family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinit ...

genealogy
, pedigree collapse describes how reproduction between two individuals who share an ancestor causes the number of distinct ancestors in the family tree of their
offspring In biology, offspring are the young creation of living organisms, produced either by a Asexual reproduction, single organism or, in the case of sexual reproduction, two organisms. Collective offspring may be known as a brood or progeny in a more ...

offspring
to be smaller than it could otherwise be. Robert C. Gunderson coined the term; synonyms include implex and the German ''Ahnenschwund'' (loosely translated: "loss of lineage").


Overview

Without pedigree collapse, a person's ancestor tree is a
binary tree In computer science Computer science deals with the theoretical foundations of information, algorithms and the architectures of its computation as well as practical techniques for their application. Computer science is the study of , ...

binary tree
, formed by the person, the parents (2), the grandparents (4), great-grandparents (8), and so on. However, the number of individuals in such a tree
grows exponentially
grows exponentially
and will eventually become impossibly high. For example, a single individual alive today would, over 30 generations going back to the
High Middle Ages The High Middle Ages, or High Medieval Period, was the period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical c ...
, have 230 or roughly a billion ancestors, more than the total
world population In demography, demographics, the world population is the total number of humans currently living, and was estimated to have exceeded 7.9 billion people . It took over 2 million years of prehistory, human prehistory and human history, history fo ...

world population
at the time. This paradox is explained by shared ancestors, referred to as pedigree collapse. Instead of consisting of all different individuals, a tree may have multiple places occupied by a single individual. This typically happens when the parents of an ancestor are related to each other (sometimes unbeknownst to themselves). For example, the offspring of two first cousins has at most only six great-grandparents instead of the usual eight. This reduction in the number of ancestors is pedigree collapse. It collapses the ancestor tree into a
directed acyclic graph In mathematics Mathematics (from Greek: ) includes the study of such topics as numbers (arithmetic and number theory), formulas and related structures (algebra), shapes and spaces in which they are contained (geometry), and quantities and ...

directed acyclic graph
. In some cultures, cousins and other relations were permitted, encouraged, or required to marry. This may have been to keep kin bonds, wealth and property within a family (
endogamy Endogamy is the practice of marrying within a specific social group In the social science Social science is the branch The branches and leaves of a tree. A branch ( or , ) or tree branch (sometimes referred to in botany ...
) or simply because there was a limited number of potential marriage partners available. Among
royalty Royalty may refer to: * Kingship * Royal family, the immediate family of a king or queen regnant, and sometimes his or her extended family * Royalty payment for use of such things as intellectual property, music, or natural resources Entertainment ...
, the frequent requirement to marry only other royals resulted in a reduced
gene pool The gene pool is the set of all gene In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular inte ...
in which most individuals were the result of extensive pedigree collapse.
Alfonso XII of Spain Alfonso XII of Spain (Alfonso Francisco de Asís Fernando Pío Juan María de la Concepción Gregorio Pelayo; 28 November 185725 November 1885), also known as El Pacificador or the Peacemaker, was King of Spain, reigning from 1874 to 1885. Afte ...

Alfonso XII of Spain
, for example, had only four great-grandparents instead of the usual eight. Furthermore, two of these great-grandparents,
Charles IV of Spain , house = BourbonBourbon may refer to: Food and drink * Bourbon whiskey, an American whiskey made using a corn-based mash * Bourbon barrel aged beer, a type of beer aged in bourbon barrels * Bourbon biscuit, a chocolate sandwich bisc ...

Charles IV of Spain
and
Maria Luisa of Parma Maria Luisa of Parma (Luisa Maria Teresa Anna; 9 December 1751 – 2 January 1819) was Queen consort of Spain House of Habsburg House of Bourbon House of Bonaparte House of Bourbon (first restoration) House of Savoy House of B ...
, who themselves were first cousins, were parents of another great-grandparent,
Maria Isabella of Spain Maria may refer to: People * Mary, mother of Jesus * Maria (given name), a popular given name in many languages Placenames Extraterrestrial *170 Maria, a Main belt S-type asteroid discovered in 1877 *Lunar maria (plural of ''mare''), large, dar ...
. Essentially, Alfonso’s parents were double first cousins, i.e. his two grandfathers were brothers and his two grandmothers were sisters, meaning there were only two sets of great-grandparents rather than four. In addition each grandfather had married one of their sister’s daughters, i.e. they had each married their sororal niece. More generally, in many cultures intermarriage may frequently occur within a small village, limiting the available gene pool.


Ancestry

The
House of Habsburg The House of Habsburg (), alternatively spelled Hapsburg in English (german: Haus Habsburg ; es, Casa de Habsburgo ; hu, Habsburg-család), also known as the House of Austria (german: link=no, Haus Österreich; es, link=no, Casa de Austria), ...
gives a well-documented example of pedigree collapse. In the case of
Charles II
Charles II
, the last Habsburg King of Spain, there were three uncle-niece marriages among the seven unions of his immediate ancestry (i.e. parents, grandparents and great-grandparents). His father and two of his great-grandfathers married their nieces. His paternal grandparents were
first cousins once removed Commonly, "cousin" refers to a "first cousin", a Kinship, relative whose most recent common ancestor with the subject is a grandparent. More generally, in the lineal kinship system used in the English-speaking world, a ''cousin'' is a type of Ki ...
, but they comprised two of the seven marriages because they were also parents to his maternal grandmother. His maternal grandparents' marriage and the final marriage of great-grandparents was between first cousins. The maximum pedigree collapse of 50% within a single generation is caused by procreation between full siblings; such children have only two different grandparents instead of the usual four. If two half-siblings procreate, their children have three grandparents instead of four (25%). If a child and parent were to procreate, their offspring would have four grandparents; so, procreation between parents and children would result in less pedigree collapse than procreation between full siblings – although one of the grandparents would also be a parent and therefore introduce no additional genes. If a person procreates with a full sibling of one of their parents (as with the uncle-niece marriages mentioned above), the offspring have four different persons as grandparents, and eight great-grandparents, but again some of these contribute no additional genes (see
Inbreeding Inbreeding is the production of offspring In biology, offspring are the young creation of living organisms, produced either by a Asexual reproduction, single organism or, in the case of sexual reproduction, two organisms. Collective offspri ...
). Small, isolated populations such as those of remote islands represent extreme examples of pedigree collapse, but the common historical tendency to marry those within walking distance, due to the relative immobility of the population before modern transport, meant that most marriage partners were at least distantly related. Even in America around the 19th century, the tendency of immigrants to marry among their ethnic, language or cultural group produced many cousin marriages. If one considers as a
function Function or functionality may refer to: Computing * Function key A function key is a key on a computer A computer is a machine that can be programmed to carry out sequences of arithmetic or logical operations automatically. Modern comp ...
of time the number of a given individual's ancestors who were alive at time , it is likely that for most individuals this function has a maximum at around 1200 AD. It was suggested in 1985 that everyone on Earth is at most 50th cousin to everyone else, based on a relatively random mating model. Simulations published in 2004 which take into account the geographical separations and less random patterns of mating in real life suggest that some populations are separated by up to a few thousand years, with a
most recent common ancestor In biology Biology is the natural science that studies life and living organisms, including their anatomy, physical structure, Biochemistry, chemical processes, Molecular biology, molecular interactions, Physiology, physiological mechanis ...
perhaps 76 generations back, though some highly remote populations may have been isolated for somewhat longer.


See also

*
Coefficient of relationship The coefficient of relationship is a measure of the degree of consanguinity (or biological relationship) between two individuals. The term coefficient of relationship was defined by Sewall Wright in 1922, and was derived from his definition of t ...
*
Consanguinity Consanguinity ("blood relation", from Latin '':wikt: consanguinitas, consanguinitas'') is the characteristic of having a kinship with another person (being descended from a common ancestor). Many jurisdictions have laws prohibiting people who ar ...

Consanguinity
*
Cousin marriage Commonly, "cousin" refers to a "first cousin", a relative Relative may refer to: General use *Kinship and family, the principle binding the most basic social units society. If two people are connected by circumstances of birth, they are sa ...
*
Galton–Watson process The Galton–Watson process is a branching process, branching stochastic process arising from Francis Galton's statistical investigation of the extinction of family names. The process models family names as patrilineal (passed from father to son ...
*
Haplotype A haplotype (haploid Ploidy () is the number of complete sets of chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. Most eukaryotic chromosomes include packaging proteins called h ...
*
Identical ancestors pointIn genetic genealogy, the identical ancestors point (IAP), or all common ancestors (ACA) point, or genetic isopoint, is the most recent point in a given population's past such that each individual alive at this point either has no living descendants, ...
* I'm My Own Grandpa *
Inbreeding Inbreeding is the production of offspring In biology, offspring are the young creation of living organisms, produced either by a Asexual reproduction, single organism or, in the case of sexual reproduction, two organisms. Collective offspri ...
* Most recent common ancestor * ''The Seven Daughters of Eve''


Notes


References

* *


External links


"How many ancestors do you have?"
by Stephen Lewis, ''The Wild Peak'', March 4, 2012 {{DEFAULTSORT:Pedigree Collapse Genealogy Incest Kinship and descent Marriage Population genetics Last common ancestors