Mitochondrial Eve

Mitochondria observed by transmission electron microscopy.

The Mitochondrial Eve is the name given to a woman considered the hypothetical most recent common ancestor through the maternal line of Humanity. Its existence is evidenced by the demonstration that there is a single lineage of mitochondria in cells of all humans.

Mitochondria are organelles that cell are transmitted only through the egg from the mother and it was shown that all human mitochondrial DNA have a common origin. The Mitochondrial Eve is the female equivalent of the Y-chromosome Adam , the most recent common ancestor by paternal lineage.

Taking into account the mutation rate (the concept of the molecular clock ), in this mtDNA, the calculations are assuming that the mitochondrial Eve lived there some 150,000 years. The phylogeny suggests it lived in Africa ^{Importance of Eve}

Although the name Bible of Eve was given him, the mitochondrial Eve was not the only individual living female of her time. Other women lived at the same time she did. These other women have also had offspring, probably some of them are also the ancestors common to humanity today, or ancestors common to only part of humanity. What characterizes the mitochondrial Eve, and all his ancestors by maternal line, is that it is the ancestor by maternal line only. Of his generation, only mitochondrial Eve produced an unbroken chain of girls to date, and it was the only one in which all living humans descend in the maternal line. The mitochondria of the other women of her era have disappeared, having been transmitted to at least one daughter. This does not mean they have no offspring, and the other women have indeed been made descendants of men and women, but not pure maternal line. The descendants of these other women will have some of their genetic makeup, but the mitochondria of their maternal ancestry, so those from the mitochondrial Eve.

The laws of chance coupled with a small population show that the slightest variation in the proportions of an allele within a population may quickly lead to its disappearance or its domination by genetic drift , although this allele has no effect differential in terms of natural selection. It is the same for the mitochondrial DNA.

The computer simulation studies indicate that Eve is perhaps not the most recent ancestor common humanity in the abstract, but the most recent common ancestor through the maternal line. Other more recent common ancestors contributed to several genes residing in the nuclear DNA linear. For example, some newer common ancestor must have sent a gene that specifies a subunit of RNA in the ribosome. However, since the reproduction mixes the nuclear DNA of chromosomes inherited from both parents, a common ancestor more recent Eve is currently difficult to identify.

Chain of events

The fact that no other female line has survived since the days of Eve seems a matter of chance rather than natural selection. An individual female acquires the title of "Eve" retroactively through an exceptional line of daughters in each generation of offspring is at least one daughter giving birth to another girl. Eve takes possession of his "title" when lines of all other contenders are interrupted, the title holder would therefore not be identified by a test during his lifetime.

Essentially, the hypothetical process by which all lineages except one go is the same as the genetic drift of alleles. As for "fixing" or the disappearance of all other alleles in the genetic drift, the process of fixing matrilineal is much slower and much less likely to occur in a large population in a small. If Eve had lived among millions of other women, it is very unlikely that the matrilineal ancestors of all humans alive today converge Eve (or other contemporary Eve).

Why the community of Eve and his fellows have been so small? One possibility is that the human population in his time has gone through a bottleneck. Another is that Eve has lived among a subpopulation of humans came supplant all others. An even more extreme version of this scenario is that Eve has had a very short life after a single event causing speciation of anatomically modern humans. Among the remains of the oldest human skeletons that were discovered, the older bones to make comparable to humans today actually date from the time when Eve lived.

The relationship to Adam

On the other hand, there is a modern man, "the Y-chromosomal Adam , "which generated an unbroken line of males who are the ancestors of all men on earth. The Y-chromosomal Adam goes back to only half the time since Eve. This means that another bottleneck, besides the one related to Eve, has affected the human lineage after it. The fact that the bottleneck at the time of Adam has also not produced a matrilineal ancestor common to all living humans - a more recent Eve, in other words - suggests that the descent and disappearance of a lineage depends on chance (unless the male line are eliminated more quickly, perhaps because of polygamy , which would have allowed only a portion of males to have offspring). Nevertheless, some researchers argue that evidence of this second bottleneck also exists in the data of mitochondrial DNA. It is also possible that the dates are wrong, that is to say that the staggered dates of Eve and Adam denote the imperfection of the theory of molecular clock, which continues to undergo revisions.

Alternative theory: transmission of paternal mitochondria?

Transmission of paternal mitochondria in oocytes ruin the theory of mitochondrial Eve. Currently, such transmission has been observed only in very rare cases, among species of mold ^, . It is therefore a bold hypothesis. If it turned out, the mitochondria are not as exclusive as marker matrilineal we had supposed. Depending on the frequency with which recombination occur, it might be that Eve never existed. However, evidence to support such a theory is still inadequate. It is now accepted that, in humans, the paternal mitochondria located in the flagellum of sperm does not pass into the oocyte.

Eve and the African

The great migration of prehistoric ' Homo sapiens reconstructed on the basis of mtDNA (dating thousands of years before present )

Sometimes called the mitochondrial Eve as an African Eve. The hypothesis is based on African examining fossils as well as analysis of mitochondrial DNA. The "family tree" (or " phylogenetic ") built on the basis of comparisons of mitochondrial DNA show that living humans whose mitochondrial lineages are the first branches of the tree are indigenous to Africa , while lineages Indigenous peoples from other continents are born of African lineages. The researchers thought that all living humans descend from Africans, some of whom have migrated out of Africa to populate the world. Also, many researchers do they like the fact Mitochondrial evidence for the "single origin" or " African Genesis ".

The construction of family trees from DNA data, however, is an inexact science. Critics of the "African Genesis" claim that the fact that mitochondria can be explained as well or even better, by placing Eve trees closer to the people of Asia. However, since 2003, following the successive advances in information technology and methods of determining the phylogenetic tree, the number of these criticisms has decreased. In any event, the biggest support that mitochondrial DNA can offer to the African origin hypothesis does not depend on trees. It is indeed among the African people found the greatest diversity of mitochondrial DNA, variations that do not appear to exist in Africa. This diversity would have accumulated, say the researchers, if humans had not lived longer in Africa than anywhere else. Sequence analysis of the Y chromosome has also given results for an African origin of hominids.

Recent discovery on the African

A recent discovery confirms the African origin of the mitochondrial Eve. Indeed, a team of researchers from the University of Cambridge has published in the journal Nature the results of their research on the theory of the origin of man . They arrived at the result that the man is actually originating from sub-Saharan Africa.

To achieve this, the team of Dr. Andrea Manica (University of Cambridge, Department of Zoology) has combined two complementary approaches: a genetic study on the different existing populations and phenotypic study of more than 6000 skeletons from several regions the planet.

Dr. Andrea Manica said: "... some have used morphological data to argue that modern humans had multiple origins. We have combined our genetic records with new measurements of a large sample of skeletons to demonstrate definitively that modern humans come from one region to the south of the Sahara in Africa. " ^,

Internal Links

• Macrohaplogroupe L (mtDNA)
• Y-chromosomal Adam
• The Seven Daughters of Eve , an attempt to explain the evolution of mitochondrial main families.

External Links

• Animation illustrating the migrations inferred from the mtDNA.
• Diagram and explanation behind this theory.

Notes

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