Drafting Human Ancestry: What Does the Neanderthal Genome Tell Us about Hominid Evolution? Commentary on Green et al. (2010) (original) (raw)

Neanderthal DNA and modern human origins

Quaternary International, 2013

Available online xxx a b s t r a c t Neanderthals are an extinct hominid lineage that coexisted with modern humans in Eurasia. The Neanderthal's role in the evolutionary history of modern humans is a well concerned topic. Mitochondrial DNA sequences from Neanderthal fossils support the "Out of Africa" theory of human evolution, suggesting that modern human ancestors replaced Neanderthal populations in Eurasia. Recent analyses of Neanderthal genome draft sequences indicate minor gene flow between Neanderthals and modern humans in Eurasia but not in Africa. However, these conclusions are quite controversial due to data quality and insufficient sampling, especially about when and where the genetic admixture took place, and the direction of the assumed gene flow.

Evaluating Neanderthal Genetics and Phylogeny

Journal of Molecular Evolution, 2007

The retrieval of Neanderthal (Homo neanderthalsensis) mitochondrial DNA is thought to be among the most significant ancient DNA contributions to date, allowing conflicting hypotheses on modern human (Homo sapiens) evolution to be tested directly. Recently, however, both the authenticity of the Neanderthal sequences and their phylogenetic position outside contemporary human diversity have been questioned. Using Bayesian inference and the largest dataset to date, we find strong support for a monophyletic Neanderthal clade outside the diversity of contemporary humans, in agreement with the expectations of the Out-of-Africa replacement model of modern human origin. From average pairwise sequence differences, we obtain support for claims that the first published Neanderthal sequence may include errors due to postmortem damage in the template molecules for PCR. In contrast, we find that recent results implying that the Neanderthal sequences are products of PCR artifacts are not well supported, suffering from inadequate experimental design and a presumably high percentage (>68%) of chimeric sequences due to ''jumping PCR'' events.

Reconstructing the genetic history of late Neanderthals

Although it has previously been shown that Neanderthals contributed DNA to modern humans 1,2 , not much is known about the genetic diversity of Neanderthals or the relationship between late Neanderthal populations at the time at which their last interactions with early modern humans occurred and before they eventually disappeared. Our ability to retrieve DNA from a larger number of Neanderthal individuals has been limited by poor preservation of endogenous DNA 3 and contamination of Neanderthal skeletal remains by large amounts of microbial and present-day human DNA 3-5. Here we use hypochlorite treatment 6 of as little as 9 mg of bone or tooth powder to generate between 1-and 2.7-fold genomic coverage of five Neanderthals who lived around 39,000 to 47,000 years ago (that is, late Neanderthals), thereby doubling the number of Neanderthals for which genome sequences are available. Genetic similarity among late Neanderthals is well predicted by their geographical location, and comparison to the genome of an older Neanderthal from the Caucasus 2,7 indicates that a population turnover is likely to have occurred, either in the Caucasus or throughout Europe, towards the end of Neanderthal history. We find that the bulk of Neanderthal gene flow into early modern humans originated from one or more source populations that diverged from the Neanderthals that were studied here at least 70,000 years ago, but after they split from a previously sequenced Neanderthal from Siberia 2 around 150,000 years ago. Although four of the Neanderthals studied here postdate the putative arrival of early modern humans into Europe, we do not detect any recent gene flow from early modern humans in their ancestry.

Using genetic evidence to evaluate four palaeoanthropological hypotheses for the timing of Neanderthal and modern human origins

Journal of Human Evolution, 2010

A better understanding of the evolutionary relationship between modern humans and Neanderthals is essential for improving the resolution of hominin phylogenetic hypotheses. Currently, four distinct chronologies for the timing of population divergence are available, ranging from the late Middle Pleistocene to the late Early Pleistocene, each based on different interpretations of hominin taxonomy. Genetic data can present an independent estimate of the evolutionary timescale involved, making it possible to distinguish between these competing models of hominin evolution. We analysed five dated Neanderthal mitochondrial genomes, together with those of 54 modern humans, and inferred a genetic chronology using multiple age calibrations. Our mean date estimates are consistent with a process of genetic divergence within an ancestral population, commencing approximately 410e440 ka. These results suggest that a reappraisal of key elements in the Pleistocene hominin fossil record may now be required.

Neanderthal Contribution to the Modern Human Gene Pool is Minor

Abstract— Neanderthals contribution to modern human’s gene pool that was made possible by their cohabitation in Europe and other small areas. The extent to their contribution varies as it depends on what was being tested. The examination of the mitochondrial DNA was the only one that gave non contradicting results. The testing of Single Nucleotide Polymorphism (SNPs), nuclear DNA and specific genes shared between the two groups based on different studies gave different results. It has been observed that Neanderthal genes have been lost through genetic drift, a bottleneck event, Neanderthal genes swamped by modern human genes as the human population grows and strong physical barriers that does not allow the two sub-species to reproduce. The multiregional theory was implemented in this study because the recent African hypothesis goes against the possible existence of both species. Transitional fossils found were taken as another indication of possible introgression. Hybrids were evolutionary dead ends and therefore no admixture could have continued that way. Fragmented fossils, modern human contamination and the limitation of the number of specimens examined made it difficult to get accurate results. The little admixture observed between the Neanderthals and modern humans may also be due to the possibility that only a few individuals from the two groups admixed or that modern humans evolved from Neanderthals. Technologies have to be made to be sensitive to DNA in order for admixtures to be observed.