Identical ancestors point

Last updated

In genetic genealogy, the identical ancestors point (IAP), also known as the 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 that point either has no living descendants, or is the ancestor of every individual alive in the present. This point lies further in the past than the population's most recent common ancestor (MRCA).

Contents

Calculation

A set of full siblings has an IAP one generation back: their parents. Similarly, double first cousins have an IAP two generations back: the four grandparents.

Considering all humans alive today and moving back in time, we eventually arrive at the MRCA to all humans. The MRCA had many contemporary companions. Many of these contemporaries had descendant lines to some people living today, but not to all people living today. Others did not have any children, or had descendants, but all descendant lines are now fully extinct.

Going further back, all the ancestors of the MRCA are also common ancestors to all humans, just not the most recent one. As we move further back in time, other common ancestors will be found on other lines, resulting in more and more of the ancient population being common ancestors. Eventually the point is reached where all people in the past population fall into one of two categories: they are common ancestors, with at least one line of descent to everyone living today, or they are the ancestors of no one alive today, because their lines of descent are completely extinct on every branch. This point in time is termed the 'identical ancestors point'.

Joseph T. Chang has proposed that in a large, well mixed population of size N, we only have to go 1.77log2 (N) generations in the past to find the time when everyone in the population (who left descendants) is an ancestor to the entire population. [1] For example, a population of 4,000 individuals would, on average, have a most recent common ancestor about 13 generations earlier and an IAP about 24 or 25 generations earlier. [1] (This model assumes random mate choice, which is unrealistic for the human population, where geographic obstacles have greatly reduced mixing across the entire population.) [1]

Of Homo sapiens

The identical ancestors point for Homo sapiens has been the subject of debate. In 2003 Rohde estimated it to be between 5000 and 15,000 years ago. [2] In 2004, Rohde, Olson and Chang showed through simulations that, given the false assumption of random mate choice without geographic barriers, the Identical Ancestors Point for all humans would be surprisingly recent, on the order of 5,000-15,000 years ago. Ralph and Coop (2013), considering the European population and working from genetics, came to similar conclusions for the recent common ancestry of Europeans. [3] [4] [ further explanation needed ] More recently, however, researchers have estimated the European isopoint to be closer to 1000 A.D. [5]

All living people share exactly the same set of ancestors before the Identical Ancestors Point, all the way to the very first single-celled organism. [3] However, people will vary widely in how much ancestry and genes they inherit from each ancestor, which will cause them to have very different genotypes and phenotypes.

This is illustrated in the 2003 simulation as follows: considering the ancestral populations alive at 5000 BC, close to the ACA point, a modern-day Japanese person will get 88.4% of their ancestry from Japan, and most of the remainder from China or Korea, with only 0.00049% traced to Norway; conversely, a modern-day Norwegian will get over 92% of their ancestry from Norway (or over 96% from Scandinavia) and only 0.00044% from Japan.

Thus, even though the Norwegian and Japanese person share the same set of ancestors, these ancestors appear in their family tree in dramatically different proportions. A Japanese person in 5000 BC with present-day descendants will likely appear trillions of times in a modern-day Japanese person's family tree, but might appear only one time in a Norwegian person's family tree. A 5000 BC Norwegian person will similarly appear far more times in a typical Norwegian person's family tree than they will appear in a Japanese person's family tree. [6]

Note that a person in the population today does not necessarily inherit any genetic material from a given ancestor at the Identical Ancestors Point. For example, a Japanese person may not inherit any genetic material from his Norwegian ancestors. In that case, they are genealogical ancestors but not genetic ancestors. The same goes even for the most recent common ancestor. [4]

See also

Related Research Articles

Common descent is a concept in evolutionary biology applicable when one species is the ancestor of two or more species later in time. According to modern evolutionary biology, all living beings could be descendants of a unique ancestor commonly referred to as the last universal common ancestor (LUCA) of all life on Earth.

<span class="mw-page-title-main">Language family</span> Group of languages related through descent from a common ancestor

A language family is a group of languages related through descent from a common ancestor, called the proto-language of that family. The term family is a metaphor borrowed from biology, with the tree model used in historical linguistics analogous to a family tree, or to phylogenetic trees of taxa used in evolutionary taxonomy. Linguists thus describe the daughter languages within a language family as being genetically related. The divergence of a proto-language into daughter languages typically occurs through geographical separation, with different regional dialects of the proto-language undergoing different language changes and thus becoming distinct languages over time.

<span class="mw-page-title-main">Mitochondrial Eve</span> Matrilineal most recent common ancestor of all living humans

In human genetics, the Mitochondrial Eve is the matrilineal most recent common ancestor (MRCA) of all living humans. In other words, she is defined as the most recent woman from whom all living humans descend in an unbroken line purely through their mothers and through the mothers of those mothers, back until all lines converge on one woman.

<span class="mw-page-title-main">Family tree</span> Chart representing family relationships in a conventional tree structure

A family tree, also called a genealogy or a pedigree chart, is a chart representing family relationships in a conventional tree structure. More detailed family trees, used in medicine and social work, are known as genograms.

<span class="mw-page-title-main">Y-chromosomal Adam</span> Patrilineal most recent common ancestor of all living humans

In human genetics, the Y-chromosomal Adam, is the patrilineal most recent common ancestor (MRCA) from whom all currently living humans are descended. He is the most recent male from whom all living humans are descended through an unbroken line of their male ancestors. The term Y-MRCA reflects the fact that the Y chromosomes of all currently living human males are directly derived from the Y chromosome of this remote ancestor.

<i>River Out of Eden</i> Book by Richard Dawkins

River Out of Eden: A Darwinian View of Life is a 1995 popular science book by Richard Dawkins. The book is about Darwinian evolution and summarizes the topics covered in his earlier books, The Selfish Gene, The Extended Phenotype and The Blind Watchmaker. It is part of the Science Masters series and is Dawkins's shortest book. It is illustrated by Lalla Ward, Dawkins's then-wife. The book's name is derived from Genesis 2:10 relating to the Garden of Eden. The King James Version reads "And a river went out of Eden to water the garden; and from thence it was parted, and became into four heads."

An ancestor, also known as a forefather, fore-elder, or a forebear, is a parent or (recursively) the parent of an antecedent. Ancestor is "any person from whom one is descended. In law, the person from whom an estate has been inherited."

<span class="mw-page-title-main">Haplotype</span> Group of genes from one parent

A haplotype is a group of alleles in an organism that are inherited together from a single parent.

The coefficient of relationship is a measure of the degree of consanguinity between two individuals. The term coefficient of relationship was defined by Sewall Wright in 1922, and was derived from his definition of the coefficient of inbreeding of 1921. The measure is most commonly used in genetics and genealogy. A coefficient of inbreeding can be calculated for an individual, and is typically one-half the coefficient of relationship between the parents.

In biology and genetic genealogy, the most recent common ancestor (MRCA), also known as the last common ancestor (LCA), of a set of organisms is the most recent individual from which all the organisms of the set are descended. The term is also used in reference to the ancestry of groups of genes (haplotypes) rather than organisms.

Genetic genealogy is the use of genealogical DNA tests, i.e., DNA profiling and DNA testing, in combination with traditional genealogical methods, to infer genetic relationships between individuals. This application of genetics came to be used by family historians in the 21st century, as DNA tests became affordable. The tests have been promoted by amateur groups, such as surname study groups or regional genealogical groups, as well as research projects such as the Genographic Project.

<span class="mw-page-title-main">Pedigree collapse</span> Concept in genealogy

In 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 to be smaller than it could otherwise be. Robert C. Gunderson coined the term; synonyms include implex and the German Ahnenschwund.

A cousin is a relative that is the child of a parent's sibling; this is more specifically referred to as a first cousin.

A genealogical DNA test is a DNA-based genetic test used in genetic genealogy that looks at specific locations of a person's genome in order to find or verify ancestral genealogical relationships, or to estimate the ethnic mixture of an individual. Since different testing companies use different ethnic reference groups and different matching algorithms, ethnicity estimates for an individual vary between tests, sometimes dramatically.

Coalescent theory is a model of how alleles sampled from a population may have originated from a common ancestor. In the simplest case, coalescent theory assumes no recombination, no natural selection, and no gene flow or population structure, meaning that each variant is equally likely to have been passed from one generation to the next. The model looks backward in time, merging alleles into a single ancestral copy according to a random process in coalescence events. Under this model, the expected time between successive coalescence events increases almost exponentially back in time. Variance in the model comes from both the random passing of alleles from one generation to the next, and the random occurrence of mutations in these alleles.

<span class="mw-page-title-main">Royal descent</span> Genealogical kinship and descent

A royal descent is a genealogical line of descent from a past or present monarch.

A surname DNA project is a genetic genealogy project which uses genealogical DNA tests to trace male lineage.

Steve Olson is an American writer who specializes in science, mathematics, and public policy. He is the author of several nonfiction trade books: Mapping Human History: Genes, Race, and Our Common Origins, which was nominated for the National Book Award in 2002; Count Down: Six Kids Vie for Glory at the World’s Toughest Math Competition in 2004; Anarchy Evolution: Faith, Science, and Bad Religion in a World Without God in 2010; Eruption: The Untold Story of Mt. St. Helens in 2016.

The Mbo people are a Bantu group of the Mbo plain, Littoral Region, Mungo Division, Nkongsamba, Southwest Region and Melong subdivisions and in the West Region, Menoua Division, Santchou Subdivision and Upper Nkam Division, Kekem Subdivision of Cameroon.

<span class="mw-page-title-main">WikiTree</span> Genealogy website

WikiTree is a genealogy website that allows users to research and to contribute to their own family trees while building and collaborating on a singular worldwide family tree within the same system. WikiTree is free for the user and financed via advertisements displayed to unregistered users. WikiTree is owned and hosted by founder's company Interesting.com, Inc.

References

  1. 1 2 3 Chang, Joseph T., ‘’Recent Common Ancestors of All Present-Day Individuals’’. 1998
  2. ↑ Rohde, DLT, On the common ancestors of all living humans Archived 2015-01-22 at the Wayback Machine . Submitted to American Journal of Physical Anthropology (2003), p. 27. "Based on the results of a series of computer models, it seems likely that our most recent common ancestor may have lived between 2,000 and 5,000 years ago. This is, perhaps, one tenth to one one-hundredth the length of time to our most recent common ancestors along solely male or solely female lines, which have been the target of considerable recent interest. The point beyond which everyone alive today shares the same set of ancestors is somewhat harder to predict, but it most likely falls between 5,000 and 15,000 years ago, with a significantly more recent date for the point at which we share nearly the same set."
  3. 1 2 Rohde DL, Olson S, Chang JT (September 2004). "Modelling the recent common ancestry of all living humans". Nature. 431 (7008): 562–6. Bibcode:2004Natur.431..562R. CiteSeerX   10.1.1.78.8467 . doi:10.1038/nature02842. PMID   15457259. S2CID   3563900.
  4. 1 2 Ralph, Peter and Coop, Graham, The Geography of Recent Genetic Ancestry across Europe, PLOS Biology, May 7, 2013, “For instance, we estimate that someone from Hungary shares on average about five genetic common ancestors with someone from the United Kingdom between 18 and 50 generations ago. Since 1/r(36) = 5.8×107, we would conservatively estimate that for every genetic common ancestor there are tens of millions of genealogical common ancestors. Most of these ancestors must be genealogical common ancestors many times over, but these must still represent at least thousands of distinct individuals.”
  5. ↑ Hershberger, Scott (Oct 5, 2020). "Humans Are All More Closely Related Than We Commonly Think". Scientific American.
  6. ↑ Rohde, DLT, On the common ancestors of all living humans Archived 2015-01-22 at the Wayback Machine . Submitted to American Journal of Physical Anthropology (2003)
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.