Please rate:
We are All Related To The Genetic Adam and

We are All Related To The Genetic Adam and


Description:

We are All Related To The Genetic Adam and Eve

Source: http://chemistry.umeche.maine.edu/CHY431/Code4.html

Source: http://en.wikipedia.org/wiki/Mitochondrial_Eve

n the field of human genetics, Mitochondrial Eve refers to the matrilineal "MRCA" (most recent common ancestor). In other words, she was the woman from whom all living humans today descend, on their mother's side, and through the mothers of those mothers and so on, back until all lines converge on one person. Because all mitochondrial DNA (mtDNA) is generally passed from mother to offspring without recombination, all mitochondrial DNA (mtDNA) in every living person is directly descended from hers by definition. Mitochondrial Eve is the female counterpart of Y-chromosomal Adam, the patrilineal most recent common ancestor, although they lived thousands of years apart.

Each ancestor (of people now living) in the line back to the matrilineal MRCA had female contemporaries such as sisters, female cousins, etc. but none of these female contemporaries of the "Mitochondrial Eve" has descendants living now in an unbroken female line.

Mitochondrial Eve is generally estimated to have lived around 200,000 years ago,[2] most likely in East Africa,[3] when Homo sapiens sapiens ("anatomically modern humans") were developing as a population distinct from other human sub-species.

Mitochondrial Eve lived much earlier than the out of Africa migration that is thought to have occurred between 95,000 to 45,000 BP.[4] The dating for 'Eve' was a blow to the multiregional hypothesis, and a boost to the hypothesis that modern humans originated relatively recently in Africa and spread from there, replacing more "archaic" human populations such as Neanderthals. As a result, the latter hypothesis is now the dominant one.

Without a DNA sample, it is not possible to reconstruct the complete genetic makeup (genome) of any individual who died very long ago. By analysing descendants' DNA, however, parts of ancestral genomes are estimated by scientists. Mitochondrial DNA (mtDNA) and Y-chromosome DNA are commonly used to trace ancestry in this manner. mtDNA is generally passed un-mixed from mothers to children of both sexes, along the maternal line, or matrilineally.[5][6] Matrilineal descent goes back to our mothers, to their mothers, until all female lineages converge.

Branches are identified by one or more unique markers which give a mitochondrial "DNA signature" or "haplotype" (e.g. the CRS is a haplotype). Each marker is a DNA base-pair that has resulted from an SNP mutation. Scientists sort mitochondrial DNA results into more or less related groups, with more or less recent common ancestors. This leads to the construction of a DNA family tree where the branches are in biological terms clades, and the common ancestors such as Mitochondrial Eve sit at branching points in this tree. Major branches are said to define a haplogroup (e.g. CRS belongs to haplogroup H), and large branches containing several haplogroups are called "macro-haplogroups".

The mitochondrial clade which Mitochondrial Eve defines is the species Homo sapiens sapiens itself, or at least the current population or "chronospecies" as it exists today. In principle, earlier Eves can also be defined going beyond the species, for example one who is ancestral to both modern humanity and Neanderthals, or, further back, an "Eve" ancestral to all members of genus Homo and chimpanzees in genus Pan. According to current nomenclature, Mitochondrial Eve's haplogroup was within mitochondrial haplogroup L because this macro-haplogroup contains all surviving human mitochondrial lineages today.

The variation of mitochondrial DNA between different people can be used to estimate the time back to a common ancestor, such as Mitochondrial Eve. This works because, along any particular line of descent, mitochondrial DNA accumulates mutations at the rate of approximately one every 3,500 years.[7][8][9] A certain number of these new variants will survive into modern times and be identifiable as distinct lineages. At the same time some branches, including even very old ones, come to an end, when the last family in a distinct branch has no daughters.

Mitochondrial Eve is the most recent common matrilineal ancestor for all modern humans. Whenever one of the two most ancient branch lines dies out, the MRCA will move to a more recent female ancestor, always the most recent mother to have more than one daughter with living maternal line descendants alive today. The number of mutations that can be found distinguishing modern people is determined by two criteria: firstly and most obviously, the time back to her, but secondly and less obviously by the varying rates at which new branches have come into existence and old branches have become extinct. By looking at the number of mutations which have been accumulated in different branches of this family tree, and looking at which geographical regions have the widest range of least related branches, the region where Eve lived can be proposed.

The date when Mitochondrial Eve lived is estimated by determining the MRCA of a sample of mtDNA lineages. In 1980, Brown first proposed that modern humans possessed a mitochondrial common ancestor that may have lived as recently as 180 kya. In 1987, Cann et al. suggested that mitochondrial Eve may have lived between 140-280 kya.
[edit] Common fallacies
[edit] Not the only woman

One of the misconceptions of mitochondrial Eve is that since all women alive today descended in a direct unbroken female line from her that she was the only woman alive at the time.[10][11] Nuclear DNA studies indicate that the size of the ancient human population never dropped below tens of thousands. There were many other women around at Eve's time with descendants alive today, but sometime in the past, those lines of descent included at least one male, who do not pass on their mother's mitochondrial DNA, thereby breaking the line of descent. By contrast, Eve's lines of descent to each person alive today includes precisely one purely matrilineal line.[10]
[edit] Not a contemporary of "Adam"

Sometimes mitochondrial Eve is assumed to have lived at the same time as Y-chromosomal Adam, perhaps even meeting and mating with him. Like mitochondrial "Eve", Y-chromosomal "Adam" probably lived in Africa; however, this "Eve" lived much earlier than this "Adam" - perhaps some 50,000 to 80,000 years earlier.[12]
[edit] Not the most recent ancestor shared by all humans
Main article: Most recent common ancestor

Mitochondrial Eve is the most recent common matrilineal ancestor, not the most recent common ancestor (MRCA). Since the mtDNA is inherited maternally and recombination is either rare or absent, it is relatively easy to track the ancestry of the lineages back to a MRCA; however this MRCA is valid only when discussing mitochondrial DNA. An approximate sequence from newest to oldest can list various important points in the ancestry of modern human populations:

The Human MRCA. All humans alive today share a surprisingly recent common ancestor, perhaps even within the last 5,000 years, even for people born on different continents.[13]
The Identical ancestors point. Just a few thousand years before the most recent single ancestor shared by all living humans comes the time at which all humans who were alive either left no descendants or are common ancestors to all humans alive today. In other words, from this point back in time "each present-day human has exactly the same set of genealogical ancestors". This is far more recent than Mitochondrial Eve.[13]
"Y-Chromosomal Adam", the most recent male-line common ancestor of all living men, was much more recent than Mitochondrial Eve, but is also likely to have been long before the Identical ancestors point.
Mitochondrial Eve, the most recent female-line common ancestor of all living people.

[edit] Implications of dating and placement of Eve
Further information: Out of Africa hypothesis, Multiregional evolution hypothesis, Recent African origin of modern humans

Initially there was a lot of resistance against the Mitochondrial Eve hypothesis. This resistance was due, in part, to the popularity of the Multiregional Evolution hypothesis amongst some leading paleoanthropologists such as Milford Wolpoff. This prevailing theory held that the evolution of humanity from the beginning of the Pleistocene 2.5 million years BP to the present day has been within a single, continuous human species, evolving worldwide to modern Homo sapiens. More resistance came from those who argued that there was too little time between Homo erectus and modern Homo sapiens to allow for another new species, and others who argued that for regional evolution from archaic hominin forms into modern ones. Consequently, the finding of a recent maternal ancestor for all humans in Africa was very controversial.

Cann, Stoneking & Wilson (1987)'s placement of a relatively small population of humans in sub-saharan Africa, lent appreciable support for the recent Out of Africa hypothesis. The current concept places between 1,500 and 16,000 effectively interbreeding individuals (census 4,500 to 48,000 individuals) within Tanzania and proximal regions. Later, Tishkoff et al. (2009) using data from many loci (not just mitochondrial DNA) extrapolated that the Angola-Namibia border region near the Atlantic Ocean is likely to be near the geographical point of origin of modern human genetic diversity. In its relatively southern origin proposals, this autosomal study was considered by the authors to be broadly consistent with a previous mitochondrial DNA studies, including one by some of the same authors which associated the origins of mitochondrial haplogroups L0 and L1 with "click languages" in southern and eastern Africa.[14]

To some extent the studies have already revealed that the presence of archaic homo sapiens in Northwest Africa (Jebel Irhoud) were not likely part of the contiguous modern human population. In addition, the older remains at Skhul and Qafzeh are also unlikely part of the constrict human population, evidence currently indicates humans expanded in the region no earlier than 90,000 BP.[citation needed] Tishkoff argues that humans might have migrated to the Levant before 90 Ka, but this colony did not persist in SW Asia.[citation needed] Better defined is the genetic separation among Neanderthals, Flores hobbit, Java man, and Peking man. In 1999 Krings et al., eliminated problems in molecular clocking postulated by Nei, 1992 when it was found the mtDNA sequence for the same region was substantially different from the MRCA relative to any human sequence. Currently there are 6 fully sequenced Neanderthal mitogenomes, each falling within a genetic cluster less diverse than that for humans, and mitogenome analysis in humans has statistically markedly reduced the TMRCA range so that it no longer overlaps with Neandertal/human split times. Of all the non-African hominids European archaics most closely resembled humans, indicating a wider genetic divide with other hominids.

Since the multiregional evolution hypothesis (MREH) revolved around a belief that regional modern human populations evolved in situ in various regions (Europe: Neandertals to Europeans, Asia: Homo erectus to East Asians, Australia: Sumatran erectines to indigenous Australians), these results demonstrated that a pure MREH hypothesis could not explain one important genetic marker.

Source: http://en.wikipedia.org/wiki/Human_migration

Historical migration of human populations begins with the movement of Homo erectus out of Africa across Eurasia about a million years ago. Homo sapiens appear to have occupied all of Africa about 150,000 years ago, moved out of Africa 70,000 years ago, and had spread across Australia, Asia and Europe by 40,000 years BC. Migration to the Americas took place 20,000 to 15,000 years ago, and by 2,000 years ago, most of the Pacific Islands were colonized. Later population movements notably include the Neolithic Revolution, Indo-European expansion, and the Early Medieval Great Migrations including Turkic expansion. In some places, substantial cultural transformation occurred following the migration of relatively small elite populations, Turkey and Azerbaijan being such examples.[3] In Britain, it is considered that the Roman and Norman conquests were similar examples, while "the most hotly debated of all the British cultural transitions is the role of migration in the relatively sudden and drastic change from Romano-Britain to Anglo-Saxon Britain", which may be explained by a possible "substantial migration of Anglo-Saxon Y chromosomes into Central England (contributing 50%-100% to the gene pool at that time."[4]

Early humans migrated due to many factors such as changing climate and landscape and inadequate food supply. The evidence indicates that the ancestors of the Austronesian peoples spread from the South Chinese mainland to Taiwan at some time around 8,000 years ago. Evidence from historical linguistics suggests that it is from this island that seafaring peoples migrated, perhaps in distinct waves separated by millennia, to the entire region encompassed by the Austronesian languages. It is believed that this migration began around 6,000 years ago.[5] Indo-Aryan migration from the Indus Valley to the plain of the River Ganga in Northern India is presumed to have taken place in the Middle to Late Bronze Age, contemporary to the Late Harappan phase in India (ca. 1700 to 1300 BC). From 180 BC, a series of invasions from Central Asia followed, including those led by the Indo-Greeks, Indo-Scythians, Indo-Parthians and Kushans in the northwestern Indian subcontinent.[6][7][8]

From 728 BC, the Greeks began 250 years of expansion, settling colonies in several places, including Sicily and Marseille. In Europe, two waves of migrations dominate demographic distributions, that of the Celtic people and that of the later Migration Period from the North and East, both being possible examples of general cultural change sparked by primarily elite and warrior migration.[citation needed] Other examples are small movements like that of the Magyars into Pannonia (modern-day Hungary). Turkic peoples spread from their homeland in modern Turkestan across most of Central Asia into Europe and the Middle East between the 6th and 11th centuries. Recent research suggests that Madagascar was uninhabited until Austronesian seafarers from Indonesia arrived during the 5th and 6th centuries AD. Subsequent migrations from both the Pacific and Africa further consolidated this original mixture, and Malagasy people emerged.[9]
One common hypothesis of the Bantu expansion

Before the expansion of the Bantu languages and their speakers, the southern half of Africa is believed to have been populated by Pygmies and Khoisan-speaking people, today occupying the arid regions around the Kalahari Desert and the forest of Central Africa. By about 1000 AD, Bantu migration had reached modern day Zimbabwe and South Africa. The Banu Hilal and Banu Ma'qil were a collection of Arab Bedouin tribes from the Arabian Peninsula who migrated westwards via Egypt between the 11th and 13th centuries. Their migration strongly contributed to the Arabization and Islamization of the western Maghreb, which was until then dominated by Berber tribes. Ostsiedlung was the medieval eastward migration and settlement of Germans. The 13th century was the time of the great Mongol and Turkic migrations across Eurasia.[10]

Between the 11th and 18th centuries, the Vietnamese expanded southward in a process known as nam tiến (southward expansion).[11] Manchuria was separated from China proper by the Inner Willow Palisade, which restricted the movement of the Han Chinese into Manchuria during the Qing Dynasty, as the area was off-limits to the Han until the Qing started colonizing the area with them later on in the dynasty's rule.[12]

The Age of Exploration and European Colonialism led to an accelerated pace of migration since Early Modern times. In the 16th century, perhaps 240,000 Europeans entered American ports.[13] In the 19th century, over 50 million people left Europe for the Americas.[14] The local populations or tribes, such as the Aboriginal people in Canada, Brazil, Argentina, Australia, Japan[15] and the United States, were usually far overwhelmed numerically by the settlers.



Previous Media Next Media
Show more Show less

0 comments

No comments yet.



 
Visit Disclose.tv on Facebook