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-unknown scientist hypothesis-
In the quest for the facts about human evolution, molecular geneticists have engaged in several major debates with paleontologists. The most recent controversial debate is about the latest phase of human evolution. One side of the argument states that modern humans evolved from their archaic forebears around the world over the past million years (The "Multiregional" Hypothesis ), whereas the other side states that all humans today can be traced along maternal lines of descent to a woman who lived about 200,000 years ago, probably in Africa. Modern humans arose in one place and spread elsewhere.
Neither the genetic information of living subjects nor the fossilised remains of dead ones can explain in isolation how, when and where populations originated. But the former evidence has a crucial advantage in determining the structure of family trees: living genes must have ancestors, whereas dead fossils may not have descendants. Molecular biologists known the genes they are examining must have been passed through lineages that survived to the present; paleontologists cannot be sure that the fossils they examine do not lead down an evolutionary "blind alley".
A genome, or full set of genes, is complete because it holds all the inherited biological information of an individual. Genomes are objective sources of data because they present evidence that has not been defined, at the outset, by any particular evolutionary model. The fossil record, on the other hand, is infamously "spotty" because a handful of surviving bones may not represent the majority of organisms that left no trace of themselves. There is yet so much that we have not yet learned or uncovered in the field of paleoanthropology. Several researchers at Cambridge University , including Martin and Robert Foley, calculated that the number of hominine species that probably lived in the period from 5 million years ago (the origin of early hominids) to 2 million years ago (the appearance of the earliest Homo) was likely to be in the vicinity of 12 to 14. The reason for this high number is also due to the fact that in the beginning of the clade speciation frequently occurs and that hominines are a geographically widespread, tropical species.
The DNA that was studied for the research into the origin of modern humans came from mitochondria, cellular organelles that convert food into a form of energy that that rest of the cell can use. Unlike the DNA of the nucleus, which forms bundles of long fibres, each consisting of a proteincoated double helix, the mitochondrial DNA comes in small, two-strand rings. Whereas nuclear DNA encodes an estimated 100,000 genes ? most of the information needed to make a human being ? mitochondrial DNA encodes only 37. For the purpose of scientists studying when lineages diverged, mitochondrial DNA has two advantages over nuclear DNA. First, the sequences in mitochondrial DNA that interest us accumulate mutations rapidly and steadily, according to empirical observations. Because many mutations do not alter the mitochondrion´s function, they are effectively neutral, and natural selection does not eliminate them.
This mitochondrial DNA therefore behaves like a fast-ticking clock, which is essential for identifying recent genetic changes. Any two humans chosen randomly from anywhere on the planet are so alike in most of their DNA sequences that we can measure evolution in our species only by concentrating on the genes that mutate fastest. Secondly, unlike nuclear DNA, mitochondrial DNA is inherited from the mother alone, unchanged except for chance mutations. For the studies of modern human origins, we focus on the mitochondrial, maternal lineages.
Logically then, all human mitochondrial DNA must have had an ultimate common female ancestor. But it is easy to show she did not necessarily live in a small population or constitute the only woman of her generation. Imagine a static population that always contains 15 mothers. Every new generation must contain 15 daughters, but some mothers will fail to produce a daughter, whereas others will produce two or more. Because materal lineages die out whenever there is no daughter to carry on, it is only a matter of time before all but one linages disappears.
Wilson´s final conclusion in the 1987 paper, merely pinpointed the region of origin for modern humans (Africa - as seen in the figure below which shows all the main findings of hominids in Africa) and estimated the time at which they arose (roughly 200,000 years ago). The female who contributed her mitochondrial DNA to the world as we know it today, was a member of a population of an estimated 10,000 individuals, all of whom were related to the founding population of modern humans; descendants of this population of various species of archaic sapiens and Homo erectus.
Therefore, the "Out of Africa" or "Mitochondrial Eve" hypothesis concludes by stating that this African population migrated into Europe from Africa and excluded Neanderthals and the hominids living there at the time.
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thanx 4 da ammo African!
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