Mitochondrial Eve A 1987 analysis of mitochondrial DNA from 147 people by Cann et al. from around the world indicated that their mitochondrial lineages all coalesced in a
common ancestor from Africa between 140,000 and 290,000 years ago. The analysis suggested that this reflected the worldwide expansion of modern humans as a new species, replacing, rather than mixing with, local archaic humans outside of Africa. Such a recent replacement scenario is not compatible with the Multiregional hypothesis and the mtDNA results led to increased popularity for the alternative
single replacement theory. According to Wolpoff and colleagues: Multiregionalists have responded to what they see as flaws in the Eve theory, and have offered contrary genetic evidences. Wu and Thorne have questioned the reliability of the
molecular clock used to date Eve. Multiregionalists point out that Mitochondrial DNA alone can not rule out interbreeding between early modern and archaic humans, since archaic human mitochondrial strains from such interbreeding could have been lost due to
genetic drift or a
selective sweep. Wolpoff for example states that Eve is "not the most recent common ancestor of all living people" since "Mitochondrial history is not population history".
Neanderthal mtDNA Neanderthal
mitochondrial DNA (
mtDNA) sequences from
Feldhofer and
Vindija Cave are substantially different from modern human mtDNA. Multiregionalists however have discussed the fact that the average difference between the Feldhofer sequence and living humans is less than that found between chimpanzee subspecies, and therefore that while Neanderthals were different
subspecies, they were still human and part of the same lineage.
Nuclear DNA Initial analysis of
Y chromosome DNA, which like mitochondrial DNA, is inherited from only one parent, was consistent with a recent African replacement model. However, the mitochondrial and Y chromosome data could not be explained by the same modern human expansion out of Africa; the Y chromosome expansion would have involved genetic mixing that retained regionally local mitochondrial lines. In addition, the Y chromosome data indicated a later expansion back into Africa from Asia, demonstrating that gene flow between regions was not unidirectional. An early analysis of 15 noncoding sites on the
X chromosome found additional inconsistencies with the recent African replacement hypothesis. The analysis found a multimodal distribution of
coalescence times to the most recent common ancestor for those sites, contrary to the predictions for recent African replacement; in particular, there were more coalescence times near 2 million years ago (
mya) than expected, suggesting an ancient population split around the time
humans first emerged from Africa as
Homo erectus, rather than more recently as suggested by the mitochondrial data. While most of these X chromosome sites showed greater diversity in Africa, consistent with African origins, a few of the sites showed greater diversity in Asia rather than Africa. For four of the 15 gene sites that did show greater diversity in Africa, the sites' varying diversity by region could not be explained by simple expansion from Africa, as would be required by the recent African replacement hypothesis. Later analyses of X chromosome and
autosomal DNA continued to find sites with deep coalescence times inconsistent with a single origin of modern humans, diversity patterns inconsistent with a recent expansion from Africa, or both. For example, analyses of a region of RRM2P4 (
ribonucleotide reductase M2 subunit
pseudogene 4) showed a coalescence time of about 2 Mya, with a clear root in Asia, while the
MAPT locus at
17q21.31 is split into two deep genetic lineages, one of which is common in and largely confined to the present European population, suggesting inheritance from Neanderthals. In the case of the
Microcephalin D allele, evidence for rapid recent expansion indicated
introgression from an archaic population. However, later analysis, including of the genomes of Neanderthals, did not find the Microcephalin D allele (in the proposed archaic species), nor evidence that it had introgressed from an archaic lineage as previously suggested. In 2001, a
DNA study of more than 12,000 men from 163 East Asian regions showed that all of them carry a mutation that originated in Africa about 35,000 to 89,000 years ago and these "data do not support even a minimal
in situ hominid contribution in the origin of anatomically modern humans in East Asia". In a 2005 review and analysis of the genetic lineages of 25 chromosomal regions,
Alan Templeton found evidence of more than 34 occurrences of gene flow between Africa and Eurasia. Of these occurrences, 19 were associated with continuous restricted gene exchange through at least 1.46 million years ago; only 5 were associated with a recent expansion from Africa to Eurasia. Three were associated with the original expansion of
Homo erectus out of Africa around 2 million years ago, 7 with an intermediate expansion out of Africa at a date consistent with the expansion of
Acheulean tool technology, and a few others with other gene flows such as an expansion out of Eurasia and back into Africa subsequent to the most recent expansion out of Africa. Templeton rejected a hypothesis of complete recent African replacement with greater than 99% certainty (
p −17).
Ancient DNA Recent analyses of DNA taken directly from Neanderthal specimens indicates that they or their ancestors contributed to the genome of all humans outside of Africa, indicating there was some degree of interbreeding with Neanderthals before their replacement. It has also been shown that Denisova hominins contributed to the DNA of Melanesians and Australians through interbreeding. By 2006, extraction of DNA directly from some archaic human samples was becoming possible. The earliest analyses were of Neanderthal DNA, and indicated that the Neanderthal contribution to modern human genetic diversity was no more than 20%, with a most likely value of 0%. By 2010, however, detailed DNA sequencing of the Neanderthal specimens from Europe indicated that the contribution was nonzero, with Neanderthals sharing 1-4% more genetic variants with living non-Africans than with living humans in sub-Saharan Africa. In late 2010, a recently discovered non-Neanderthal archaic human, the
Denisova hominin from south-western Siberia, was found to share 4–6% more of its genome with living Melanesian humans than with any other living group, supporting admixture between two regions outside of Africa. In August 2011,
human leukocyte antigen (HLA) alleles from the archaic Denisovan and Neanderthal genomes were found to show patterns in the modern human population demonstrating origins from these non-African populations; the ancestry from these archaic alleles at the HLA-A site was more than 50% for modern Europeans, 70% for Asians, and 95% for Papua New Guineans. Proponents of the multiregional hypothesis believe the combination of regional continuity inside and outside of Africa and lateral gene transfer between various regions around the world supports the multiregional hypothesis. However, "Out of Africa" Theory proponents also explain this with the fact that genetic changes occur on a regional basis rather than a continental basis, and populations close to each other are likely to share certain specific regional SNPs while sharing most other genes in common. Migration Matrix theory (A=Mt) indicates that dependent upon the potential contribution of Neanderthal ancestry, we would be able to calculate the percentage of Neanderthal mtDNA contribution to the human species. As we do not know the specific migration matrix, we are unable to input the exact data, which would answer these questions irrefutably. ==See also==