Il colore dei mesolitici

Gli studi più recenti lasciano concludere che i cacciatori raccoglitori europei (in questo caso, della Spagna) del Mesolitico avevano la pelle scura. analogamente a quelli indiani. Poi, per un processo che fu - più probabilmente - di selezione ed incroci, la colorazione si schiarì, in modo più completo in europa ed in modo variegato in India. Un altro fatto rilevante - anche se più tecnico - è l'appartenenza allall'aplogruppo Y C6: questo permette di concludere che l'aplogruppo C6 sia stato pan-eurasiatico. Ciò è importante, in quanto sembra essere legato a più elevate difese contro le infezioni, che sarebbero divenute indubbiamente più frequenti con l'introduzione dell'allevamento e la maggiore densità di popolazione del Neolitico.

Gli Europei di 7.000 anni fa avevano occhi blu e pelle scura: l'aspetto delle antiche popolazioni di cacciatori-raccoglitori è stato ricostruito per la prima volta grazie all'analisi del Dna dei resti di un individuo vissuto nel Mesolitico in Spagna. Il risultato, pubblicato sulla rivista Nature, si deve al gruppo coordinato da Carles Lalueza-Fox, dell'Istituto di Biologia Evolutiva a Barcellona.

I resti dell'uomo sono stati scoperti nel 2006 con un altro scheletro maschile nel sito La Brana - Arintero in Valdelugueros, nel Nord della Spagna. Entrambi gli uomini sono vissuti nel Mesolitico, il periodo compreso fra 10.000 a 5.000 anni fa (tra il Paleolitico e Neolitico), che si conclude con l'avvento dell'agricoltura e l'allevamento, pratiche arrivate dal Medio Oriente.

La ricerca è stata condotto sul Dna estratto da un dente di uno dei due uomini, indicato come La Brana 1. L'analisi mostra come alcune nuove abitudini introdotte dall'agricoltura abbiano influenzato le popolazioni, facendo emergere nuovi geni associati con il sistema immunitario e la dieta. L'arrivo del Neolitico, con una dieta a base di carboidrati e nuovi agenti (come virus batteri e parassiti) trasmessi dagli animali domestici, ha comportato infatti problemi metabolici e immunologici che si sono tradotti in adattamenti genetici nelle popolazioni. Tra questi vi è la capacità di digerire il lattosio, che il cacciatore-raccoglitore di La Brana infatti non aveva.

L'uomo aveva anche difficoltà a digerire gli alimenti contenenti amidi rispetto agli agricoltori del Neolitico. Per quanto riguarda l'aspetto fisico: il mix di occhi azzurri, pelle d'ebano e capelli scuri suggerisce che il passaggio alla pelle più chiara degli europei moderni era ancora in corso durante il Mesolitico ma il colore degli occhi era cambiato prima. ''La sorpresa più grande - osserva Lalueza-Fox - è stata scoprire che questa persona possedeva versioni dei geni africani che determinano la pigmentazione della pelle, il che indica che aveva la pelle scura, anche se non possiamo stabilire l'esatta tonalità''. Ma per l'esperto, ancora più sorprendente è, contemporaneamente, la presenza di geni responsabili degli occhi azzurri negli europei di oggi.

Il Dna dell'antico uomo racconta anche le sue parentele: aveva un antenato comune con i coloni del sito Paleolitico di Mal'ta, vicino al lago Baikal in Siberia. Inoltre i suoi 'parenti' attuali potrebbero essere nel Nord Europa, come Svezia e Finlandia, le cui popolazioni sono le più vicine sotto il profilo genetico. Dati, conclude Lalueza-Fox, che indicano ''una continuità genetica nelle popolazioni dell'Eurasia centrale e occidentale''.

Brown-skinned, blue-eyed, Y-haplogroup C-bearing European hunter-gatherer from Spain (Olalde et al. 2014)

Ricostruzione ipotetica dell'aspetto di un cacciatore raccoglitore mesolitico europeo: pelle scura, occhi azzurri

There is nothing like a little ancient DNA weirdness to start off 2014, which promises to be as exciting as 2013 was.

The new study La Brana 1 identifies it as ancestral in the SLC24A5 locus in which virtually all Europeans are derived. This comes in the heels of the Loschbour preprint which identified that sample from Luxembourg as also being ancestral. Taken together, it's now clear that hunter-gatherers from Mesolithic Western Europe were brown.

Curiously, it now seems that both Europe and India were (in part) inhabited by brown people and became lighter by a process of admixture + selection. The process went "all the way" in Europe, but a cline of pigmentation was sustained in India.

The other finding (not mentioned in the abstract) is that La Brana 1 belonged to Y-haplogroup C6! This is a low-frequency European clade of haplogroup C. So now, we have evidence that haplogroup C is not eastern Eurasian (as the presence of its subclades in Australia, India, East Asia, and the Americas might suggest), but a pan-Eurasian entity. It remains to be seen whether this C-in-Europe can be pushed further back in time, but finding it in Mesolithic Iberia reduces the chance that it's some random eastern Eurasian who made it to the outskirts of Europe recently.

Finally, La Brana 1 has derived alleles at loci associated with pathogen resistance. This might be important, because a common hypothesis is that Europeans developed this type of resistance during the Neolithic as they started interacting with the pathogens of domesticated species and started living in less-hygienic higher-density settlements.


Nature (2014) doi:10.1038/nature12960

Derived immune and ancestral pigmentation alleles in a 7,000-year-old Mesolithic European 

Iñigo Olalde et al.

Ancient genomic sequences have started to reveal the origin and the demographic impact of farmers from the Neolithic period spreading into Europe1, 2, 3. The adoption of farming, stock breeding and sedentary societies during the Neolithic may have resulted in adaptive changes in genes associated with immunity and diet. However, the limited data available from earlier hunter-gatherers preclude an understanding of the selective processes associated with this crucial transition to agriculture in recent human evolution. Here we sequence an approximately 7,000-year-old Mesolithic skeleton discovered at the La Braña-Arintero site in León, Spain, to retrieve a complete pre-agricultural European human genome. Analysis of this genome in the context of other ancient samples suggests the existence of a common ancient genomic signature across western and central Eurasia from the Upper Paleolithic to the Mesolithic. The La Braña individual carries ancestral alleles in several skin pigmentation genes, suggesting that the light skin of modern Europeans was not yet ubiquitous in Mesolithic times. Moreover, we provide evidence that a significant number of derived, putatively adaptive variants associated with pathogen resistance in modern Europeans were already present in this hunter-gatherer.

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Spanish hunter-gatherer had blue eyes and dark skin 

La Braña 1, name used to baptize a 7,000 years old individual from the Mesolithic Period, whose remains were recovered at La Braña-Arintero site in Valdelugueros (León, Spain) had blue eyes and dark skin. These details are the result of a study conducted by Carles Lalueza-Fox, researcher from the Spanish National Research Council (CSIC), in collaboration with the Centre for GeoGenetics (Denmark). La Braña 1 represents the first recovered genome of an European hunter-gatherer. The research is published in Nature 

The skeleton of La Braña 1, as it was discovered in 2006 [Credit: J.M. Vidal Encina] 

The Mesolithic, a period that lasted from 10,000 to 5,000 years ago (between the Paleolithic and the Neolithic), ends with the advent of agriculture and livestock farming, coming from the Middle-East. The arrival of the Neolithic, with a carbohydrate-based diet and new pathogens transmitted by domesticated animals, entailed metabolic and immunological challenges that were reflected in genetic adaptations of post-Mesolithic populations. Among these is the ability to digest lactose, which La Braña individual could not do. Lalueza-Fox states: "However, the biggest surprise was to discover that this individual possessed African versions in the genes that determine the light pigmentation of the current Europeans, which indicates that he had dark skin, although we can not know the exact shade." 

La Braña 1, the name used to baptize a 7,000-year-old individual from the Mesolithic Period, had blue eyes and dark skin [Credit: Spanish National Research Council] 

CSIC researcher, who works at the Institute of Evolutionary Biology (a joint centre of CSIC and the University Pompeu Fabra (UPF), located in Barcelona, adds: "Even more surprising was to find that he possessed the genetic variations that produce blue eyes in current Europeans, resulting in a unique phenotype in a genome that is otherwise clearly northern European." The study of the genome suggests that current populations nearest to La Braña 1 are in northern Europe, such as Sweden and Finland. In addition, the work points out that La Braña 1 has a common ancestor with the settlers of the Upper Paleolithic site of Mal'ta, located in Lake Baikal (Siberia), whose genome was recovered a few months ago. Lalueza-Fox concludes: "These data indicate that there is genetic continuity in the populations of central and western Eurasia. In fact, these data are consistent with the archeological remains, as in other excavations in Europe and Russia, including the site of Mal'ta, anthropomorphic figures -called Paleolithic Venus- have been recovered and they are very similar to each other." 

Frontal view of the La Braña 1 skull [Credit: J.M. Vidal Encina] 

DNA with an "exceptional" preservation La Braña-Arintero site was discovered by chance in 2006 and excavated by Julio Manuel Vidal Encinas, archeologist of the Council of Castilla y León. The cave, located in a cold mountainous area with a steady temperature and 1,500 meters below the sea level, contributed to the "exceptional" preservation of the DNA from two individuals found inside, and they were called La Braña 1 and La Braña 2. According to Iñigo Olalde, lead author of the study, "the intention of the team is to try to recover the genome of the individual called La Braña 2, which is worse preserved, in order to keep obtaining information about the genetic characteristics of these early Europeans." Source: Spanish National Research Council (CSIC) [January 26, 2014]

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Effetto della prima agricoltura sull'umanità

Early agriculture had dramatic effects on 

humans

The introduction of agriculture in Europe was followed by regional population crashes despite trends of demographical growth, reports research published in Nature Communications this week. Sean Downey, assistant professor in the University of Maryland's Department of Anthropology, was co-author of the paper. The work suggests that these sharp population decreases weren't due to changing climatic conditions, and therefore the authors propose internal causes. The research represents a major revision to our understanding of how the introduction of agricultural technology impacted humans.

Map of Central and North Western Europe. Points indicate archaeological site locations and colours delineate the sub-regions used to estimate demographic patterns [Credit: Nature Communications/doi:10.1038/ncomms3486]

Stephen Shennan, professor of theoretical archaeology at the Institute of Archaeology, University College London, received grant funding from the European Research Council to study early agriculture and its impact on populations across Europe. His multidisciplinary team of researchers includes co-author Downey, and Mark Thomas, Research Department of Genetics, Evolution and Environment, University College London, who designed the statistical analysis necessary to produce the findings.

Agriculture was introduced in the Aegean (modern day Turkey) around 8,500 years ago and steadily spread across Europe, reaching France around 7,800 years ago, and Britain, Ireland and northern Europe approximately 6,000 years ago. In all instances, the introduction of agriculture meant a drastic change in food production and consumption patterns, which led to a population boom. Utilizing radiocarbon dating, and an innovative new method for improving the accuracy of this data, the study's authors examined how population levels changed over time across Europe during the late Mesolithic, ("Middle Stone age") and Early Neolithic ("New Stone age").

The research team discovered that, in all of the 12 different European regions studied, from the South of France to Scotland and Denmark, drastic population fluctuations can be observed. In fact, they note that in some cases population declines were as significant as 30-60 percent from the highest levels achieved after the introduction of agriculture. These dramatic changes in population are of similar scale to the decrease estimated for the much later "Black Death".

The authors found that those fluctuations cannot be associated with climatic factors; however, the exact reasons for this population decline remains unknown.

"It's striking that the development of agriculture – one of humanity's major evolutionary steps – failed to buffer against widespread social collapse during this early period of rapid population growth in Europe," explains Downey. "At this point in the research we can only speculate at the direct causes, but the study demonstrates that agriculture-based societies in the past were vulnerable to population collapse on a broad scale." Downey continues by explaining the study's finding: "There were no correlations between the collapse of regional populations and known climate shifts. It wasn't the climate, so we think it must have been the long-term impact new agricultural technologies had on local environments in reducing resources. The stress this caused among farmers was likely exacerbated by other well-known consequences of living in higher-density populations: increased incidence of social conflict and of disease."

Source: University of Maryland [October 01, 2013]