I took a class from João Zilhão last term – “Emergence of Modern Humans” – really, all Neandertals, all the time. Zilhão has been one of the most outspoken advocates for Neandertal/modern human admixture so the recent genome analysis was a vindication – making it all the perfect timing to take a class from him.
In other news, though, it’s been a big year for Neandertals.
Sequencing the Neanderthal Genome
Green, R.E. et al., 2010. A Draft Sequence of the Neandertal Genome. Science, 328 (May), pp.710 – 722.
“The analysis of the Neandertal genome shows that they are likely to have had a role in the genetic ancestry of present-day humans outside of Africa, although this role was relatively minor given that only a few percent of the genomes of present-day people outside Africa are derived from Neandertals. Our results also point to a number of genomic regions and genes as candidates for positive selection early in modern human history, for example, those involved in cognitive abilities and cranial morphology….
“Mutations in several genes…. have been associated with diseases affecting cognitive capacities. DYRK1A, which lies in the Down syndrome critical region, is thought to underlie some of the cognitive impairment associated with having three copies of chromsome 21 (64). Mutations in NRG3 have been associated with schizophrenia, a condition that has been suggested to affect human- specific cognitive traits (65, 66). Mutations in CADPS2 have been implicated in autism (67), as have mutations in AUTS2 (68). Autism is a developmental disorder of brain function in which social interactions, communication, activity, and interest patterns are affected, as well as cognitive aspects crucial for human sociality and culture(69). It may thus be that multiple genes involved in cognitive development were positively selected during the early history of modern humans. One gene of interest may beRUNX2 (CBFA1). It is the only gene in the genome known to cause cleidocranial dysplasia, which is characterized by delayed closure of cranial sutures, hypoplastic or aplastic clavicles, a bell-shaped rib cage, and dental abnormalities (70). Some of these features affect morphological traits for which modern humans differ from Neandertals as well as other earlier hominins. For example, the cranial malformations seen in cleidocranial dysplasia include frontal bossing, i.e., a protruding frontal bone. A more prominent frontal bone is a feature that differs between modern humans and Neandertals as well as other archaic hominins. The clavicle, which is affected in cleidocranial dysplasia, differs in morphology betwee nmodern humans and Neandertals (71) and is associated with a different architecture of the shoulder joint. Finally, a bell-shaped rib cage is typical of Neandertals and other archaic hominins. A reasonable hypothesis is thus that an evolutionary change in RUNX2 was of importance in the origin of modern humans and that this change affected aspects of the morphology of the upper body and cranium.”
Definitive proof of Neanderthals and humans interbred
The main point – or at least the one that got all the attention…
John Hawks: NEANDERTHALS LIVE!
Especially when its compared to mtDNA studies…
And how they interbred… sexual selection favouring sexual dimorphism, or subsequent natural selection?
PLoS Neuroanthropology: The Neanderthal Romeo and Human Juliet Hypothesis
Scientists have had trouble reconciling data from analyses of human mitochondrial DNA and the male Y chromosome. Analyses of human mitochondrial DNA indicate that we all share a common female ancestor 170,000 years ago. Analyses of the Y chromosome indicate that we share a common male ancestor 59,000 years ago.
If Haldane’s Law applied to the offspring of H.neanderthalensis and H.sapiens, we would expect to find female hybrids quite commonly, but male hybrids much more rarely. The male hybrids would have carried a Y chromosome very similar to that of the original hybridizing male. The lack of Neanderthal mtDNA suggests that the initial hybridization involved a Neanderthal male, but there would probably have been few if any male hybrid offspring, so the Neanderthal Y chromosome and the mtDNA would have been quickly lost. Nonetheless, the Neanderthal autosomes would have happily mingled and interchanged with human autosomes, eventually losing their identity in the process.
Could it be that Homo neanderthalensis males were able to mate with Homo sapiens females but that the reciprocal cross was unsuccessful? Alternatively, were male H.sapiens disastrously incapable of wooing the physically more powerful H.neanderthalensis females? Or were H.neanderthalensis females simply unable to give birth to hybrid offspring? Perhaps male H.neanderthalensis outcompeted early male H.sapiens and eventually the male Neanderthal genes gained dominance (and maybe H.sapiens females somehow out-competed H.neanderthalensis females for partners). All of these possibilities potentially explain how we share a common male ancestor 59,000 years ago, but a common female ancestor 170,000 years ago. Simultaneously, these hypotheses explain why comparisons of DNA sequences in mitochondrial DNA from Neanderthals and modern humans have indicated that there was no interbreeding between these two exceedingly similar species.
Lari, M. et al., 2010. The Microcephalin Ancestral Allele in a Neanderthal Individual. J. Hawks, ed. PLoS ONE, 5(5), p.e10648. <http://dx.plos.org/10.1371/journal.pone.0010648>
Background: The high frequency (around 0.70 worlwide) and the relatively young age (between 14,000 and 62,000 years) of a derived group of haplotypes, haplogroup D, at the microcephalin (MCPH1) locus led to the proposal that haplogroup D originated in a human lineage that separated from modern humans .1 million years ago, evolved under strong positive selection, and passed into the human gene pool by an episode of admixture circa 37,000 years ago. The geographic distribution of haplogroup D, with marked differences between Africa and Eurasia, suggested that the archaic human form admixing with anatomically modern humans might have been Neanderthal.
Methodology/Principal Findings: Here we report the first PCR amplification and high- throughput sequencing of nuclear DNA at the microcephalin (MCPH1) locus from Neanderthal individual from Mezzena Rockshelter (Monti Lessini, Italy). We show that a well-preserved Neanderthal fossil dated at approximately 50,000 years B.P., was homozygous for the ancestral, non-D, allele. The high yield of Neanderthal mtDNA sequences of the studied specimen, the pattern of nucleotide misincorporation among sequences consistent with post-mortem DNA damage and an accurate control of the MCPH1 alleles in all personnel that manipulated the sample, make it extremely unlikely that this result might reflect modern DNA contamination.
Conclusions/Significance: The MCPH1 genotype of the Monti Lessini (MLS) Neanderthal does not prove that there was no interbreeding between anatomically archaic and modern humans in Europe, but certainly shows that speculations on a possible Neanderthal origin of what is now the most common MCPH1 haplogroup are not supported by empirical evidence from ancient DNA.
A sample of size one is clearly insufficient to reject any hypothesis, but within these strong restrictions, MLS is the first Neanderthal individual genotyped at the MCPH1 locus and does not cluster within haplogroup-D. Along with the simulations of Ref. 5, this result indicates that at present we do not need either positive selection, or an origin outside African populations of Homo sapiens sapiens, to account for the observed patterns of modern MCPH1 variation.
Different post-natal brain development
Gunz, P. et al., 2010. Brain development after birth differs between Neanderthals and modern humans. Current Biology, 20(21), p.R921–R922. <http://linkinghub.elsevier.com/retrieve/pii/S0960982210012820>
The difference between the developmental patterns of modern humans and Neanderthals is most prominent directly after birth, when the shape of the vault is extremely sensitive to the tempo and mode of brain growth.. When the cranial bones are thin and not yet fully ossified, the shape changes of the frontal and parietal bone are largely driven by the increase in brain volume. While the growth of the face affects the shape of the cranial base [6,7], it is unlikely that this alone could explain the shape changes of the parietal and occipital bone shown in Figure 1. We suggest, therefore, that species differences in brain growth rates [4,5] and timing underlie the uniquely modern human globularization phase.
The development of cognitive abilities during individual growth is linked to the maturation of the underlying neural circuitry: in humans, major internal brain reorganization has been documented until adolescence, and even subtle alterations of pre- and perinatal brain development have been linked to changes of the neural wiring pattern that affect behavior and cognition . The uniquely modern human pattern of early brain development is particularly interesting in the light of the recent breakthroughs in the Neanderthal genome project , which identified genes relevant to cognition that are derived in living humans.
Band of brothers
Lalueza-Fox, C. et al., 2010. Genetic evidence for patrilocal mating behavior among Neandertal groups. Proceedings of the National Academy of Sciences, pp.10-13.
The remains of 12 Neandertal individuals have been found at the El Sidrón site (Asturias, Spain), consisting of six adults, three adoles- cents, two juveniles, and one infant. Archaeological, paleonto- logical, and geological evidence indicates that these individuals represent all or part of a contemporaneous social group of Nean- dertals, who died at around the same time and later were buried together as a result of a collapse of an underground karst. We sequenced phylogenetically informative positions of mtDNA hyper- variable regions 1 and 2 from each of the remains. Our results show that the 12 individuals stem from three different maternal lineages, accounting for seven, four, and one individual(s), respectively. Using a Y-chromosome assay to confirm themorphological determination of sex for each individual, we found that, although the three adult males carried the same mtDNA lineage, each of the three adult females carried different mtDNA lineages. These findings provide evidence to indicate that Neandertal groups not only were small and characterized by low genetic diversity but also were likely to have practiced patrilocal mating behavior.
Victims of a Natural Disaster
Golovanova, L.V. et al., 2010. Significance of Ecological Factors in the Middle to Upper Paleolithic Transition. Current Anthropology, 51(5), pp.655-691.
New York TImes: Neanderthals’ Big Loss in Battle of the Elements
And there’s the geomagnetic lake theory – neither catchy enough to make headlines, nor seeming to have sparked much response…
Valet, J.-P. & Valladas, H., 2010. The Laschamp-Mono lake geomagnetic events and the extinction of Neanderthal: A causal link or a coincidence? Quaternary Science Reviews, 29(27-28), pp.3887-3893. <http://linkinghub.elsevier.com/retrieve/pii/S0277379110003434>
So much for morphological pattern as cold climate adaptation?
Rae, T.C., Koppe, T. & Stringer, C.B., 2010. The Neanderthal face is not cold adapted. Journal of human evolution, 60(2), pp.234-239.
Many morphological features of the Pleistocene fossil hominin Homo neanderthalensis, including the reputed large size of its paranasal sinuses, have been interpreted as adaptations to extreme cold, as some Neanderthals lived in Europe during glacial periods. This interpretation of sinus evolution rests on two assumptions: that increased craniofacial pneumatization is an adaptation to lower ambient tempera-tures, and that Neanderthals have relatively large sinuses. Analysis of humans, other primates, and rodents, however, suggests that the first assumption is suspect; at least the maxillary sinus undergoes a significant reduction in volume in extreme cold, in both wild and laboratory conditions. The second assumption, that Neanderthal sinuses are large, extensive, or even ‘hyperpneumatized,’ has held sway since the first specimen was described and has been interpreted as the causal explanation for some of the distinctive aspects of Neanderthal facial form, but has never been evaluated with respect to scaling. To test the latter assumption, previously published measurements from two-dimensional (2D) X-rays and new three-dimensional (3D) data from computed tomography (CT) of Neanderthals and temperate- climate European Homo sapiens are regressed against cranial size to determine the relative size of their sinuses. The 2D data reveal a degree of craniofacial pneumatization in Neanderthals that is both commensurate with the size of the cranium and comparable in scale with that seen in temperate climate H. sapiens. The 3D analysis of CT data from a smaller sample supports this conclusion. These results suggest that the distinctive Neanderthal face cannot be interpreted as a direct result of increased pneumatization, nor is it likely to be an adaptation to resist cold stress; an alternative explanation is thus required.
And, back to complicating the “were they as smart as us” and “if they were, wouldn’t they have…” debate
Higham, T. et al., 2010. Chronology of the Grotte du Renne (France) and implications for the context of ornaments and human remains within the Chatelperronian. Proceedings of the National Academy of Sciences, pp.1-6.
The site of the Grotte du Renne (at Arcy-sur-Cure) is of great importance because it provides the most persuasive evidence for behavioral complexity among Nean- derthals. A range of ornaments and tools usually associated with modern human industries, such as the Aurignacian, were excavated from three of the Châtelperronian levels at the site, along with Neanderthal fossil remains (mainly teeth). This extremely rare occur- rence has been taken to suggest that Neanderthals were the crea- tors of these items.Whether Neanderthals independently achieved this level of behavioral complexity and whether this was culturally transmitted or mimicked via incoming modern humans has been contentious. At the heart of this discussion lies an assumption re- garding the integrity of the excavated remains. One means of testing this is by radiocarbon dating;however, until recently, our ability to generate both accurate and precise results for this period has been compromised. A series of 31 accelerator mass spectrometry ultrafiltered dates on bones, antlers, artifacts, and teeth from six key archaeological levels shows an unexpected degree of variation. This suggests that some mixing of material may have occurred, which implies a more complex depositional history at the site and makes it difficult to be confident about the association of artifacts with human remains in the Châtelperronian levels.
Daniau, A.-L., dʼErrico, F. & Sánchez Goñi, M.F., 2010. Testing the hypothesis of fire use for ecosystem management by neanderthal and upper palaeolithic modern human populations. PloS one, 5(2), p.e9157.
Extensive use of fire for ecosystem management was probably a component of the technical package of Modern Humans during their colonisation of Southeast Asia. Our study shows that fire regimes in Western Europe between 70 ka and 10 ka were mainly driven by the D-O millennial-scale climatic variability and its impacts on fuel load. At a macro level at least, the colonisation of Western Europe by Anatomically Modern Humans did not have a detectable impact on fire regimes. This, however, does not mean that Neanderthals and/or Modern Humans did not use fire for ecosystem management but rather that, if this were indeed the case, the impact on the environment of fire use is not detectable in our records, and was certainly not as pronounced as it was in the biomass burning history of Southeast Asia.
Did I miss any?
Feature Image: from phys.org/ original credits to John Gurche, artist / Chip Clark, photographer