Friday, 20 May 2022

Evolution News - How the Maltese Evolved a Distinct Genome in Isolation

Reconstructed view of the burial caves of the Xagħra Circle
(Libby Mulqueeney after an original by Caroline Malone).

Source: Malone et al.2009. Mortuary Customs in Prehistoric Malta.Cambridge: McDonald, pp 375, 377. Malone, C., Stoddart, S., Trump, D. & Bonanno, A. (eds.). 2009. Mortuary Customs in prehistoric Malta. Excavations at the Brochtorff Circle at Xagħra (1987-1994). Cambridge: McDonald Institute.
How seascapes of the ancient world shaped genetic structure of European populations - Trinity News and Events

A group of researchers from Trinity College, Dublin, Ireland, and their international colleagues, have shown how relative isolation on the small Mediterranean islands of Malta (and neighbouring Gozo) produced distinct genomes in the population, due to a combination of the 'founder effect' and a small population reduced at time to just a few hundred inbred individuals.

Contrary to current thinking, which sees oceans as highways at the time, allowing migration and mixing more easily than travel overland, this result suggests that over the period in question, the Mediterranean acted as a barrier to isolate the population of Malta, consequently they failed to acquire some of the genetic signatures that mark migration across the rest of Europe at the time.

Analysis of the genome of ancient (4500–5000-year-old) individuals from a cave burial at the Xagħra Circle on Gozo, compared to the genomes of individuals of the same age from burial sites around Europe, show evidence of a small population numbering in the hundreds and of inbreeding, which is to be expected of a small, isolated population. One of the individuals examined turned out to be the offspring of second-degree relatives.

The Trinity College News release explains:
Scientists recreated the genetic geography across the whole of Europe at the time of the earliest farmers. They found evidence that it was fundamentally shaped by its seascapes which include barriers distinguishing Ireland and Britain from the continental mainland, and especially distinguishing the populations from the Scottish Orkney islands. These examples are powerful illustrations of genomic insularity. For genes at least, the seaways were more retardant than accelerant of connection.

Was the sea a barrier or a highway in connecting regions during ancient times? Our research shows that seafaring increased the differentiation between populations from islands and mainland Europe. Thanks to the analysis of hundreds of ancient genomes we discovered a level of structure among populations that correlates with their geographic location. This unprecedented level of resolution will most likely lead to new theories about migration and seafaring.

Bruno Ariano, first author.
PhD student at Trinity College Dublin,
Now also Senior Bioinformatician at Open Target.
The Xagħra Circle, Gozo
The first settlers in the Maltese islands were Neolithic, dated by Queen’s University from the sixth millennium BC. Communities developed through a series of cultural phases, with some material indications of external connectivity. Maltese culture flourished from 3600 BC with distinctive craft and architecture only found on the islands. One example was the development of elaborate mortuary structures, such as the Xagħra circle, Gozo. This monumentalized underground tomb yielded the remains of hundreds of individuals and underwent remodelling and enlargement until around 2500 BC when it was abandoned, possibly as part of a wider population decline or replacement.

The builders of the temples of prehistoric Malta showed enormous resilience and creativity for over a thousand years, as confirmed by a detailed dating programme at Queen’s Belfast. The new biological evidence demonstrates that they were also challenged by the maritime distance of their island home.

Professor Caroline Malone, co-author.
Professor of Prehistory
School of Natural and Built Environment
Queens University Belfast, Northern Ireland, UK.
To examine the demography of Late Neolithic Malta, scientists sequenced genomes from this burial site. The elucidation of fine structure among closely related groups such as European Neolithic populations is challenging, and requires a fine scale genetic analysis. Therefore, to examine these in a wider context, the team additionally imputed genome wide diploid genotypes from published ancient genomes and assessed long chunks of genomes shared within and between genomes to estimate genetic geography and demographies across Neolithic Europe.

For the first time, we have a scientific understanding of the scale of prehistoric society in Malta. These results suggest that small communities were closely associated with the guardianship of the famous temples.

Professor Simon Stoddart, co-author
Professor of Prehistory
Department of Archaeology
University of Cambridge, England, UK.
A high resolution picture of the genetic background of ancient human populations allowed scholars to unveil their history, relatedness and migration. For example, it was discovered that ancient Neolithic people from Malta experienced an unusual drop in their size perhaps because of external factors such as the deterioration of the local environment and economy. Moreover, the genetic structure of modern human populations in Europe was mostly already present in the ancient communities that lived thousands of years ago. This discovery will surely open new questions about seafaring in ancient times.
Graphical Abstract


Copyright: © 2022 The authors.
Published by Elsivier Inc. Open access (CC BY 4.0)
The team's research was published two days ago in the journal, Current Biology:
Highlights
  • Three inbred genomes from Malta, dated around 2500 BC
  • As in moderns, the genetic structure of Neolithic genomes is shaped by geography
  • Genomic insularity of island Neolithic populations
  • A marked distinction between the Danubian and Mediterranean farming expansion routes

Summary

Archaeological consideration of maritime connectivity has ranged from a biogeographical perspective that considers the sea as a barrier to a view of seaways as ancient highways that facilitate exchange. Our results illustrate the former. We report three Late Neolithic human genomes from the Mediterranean island of Malta that are markedly enriched for runs of homozygosity, indicating inbreeding in their ancestry and an effective population size of only hundreds, a striking illustration of maritime isolation in this agricultural society. In the Late Neolithic, communities across mainland Europe experienced a resurgence of hunter-gatherer ancestry, pointing toward the persistence of different ancestral strands that subsequently admixed. This is absent in the Maltese genomes, giving a further indication of their genomic insularity. Imputation of genome-wide genotypes in our new and 258 published ancient individuals allowed shared identity-by-descent segment analysis, giving a fine-grained genetic geography of Neolithic Europe. This highlights the differentiating effects of seafaring Mediterranean expansion and also island colonization, including that of Ireland, Britain, and Orkney. These maritime effects contrast profoundly with a lack of migratory barriers in the establishment of Central European farming populations from Anatolia and the Balkans.

What this paper shows, apart from the surprising role of seas as barriers to migration, is that, exactly as the Theory of Evolution predicts, an isolated population will evolve a distinct genome and this tendency is accelerated if the population is small or goes through narrow bottlenecks as seems to have happened on Malta and Gozo. The record of these ancient people is a record of the beginnings of allopatric speciation, such as must have happened multiple times and in multiple locations during the course of human evolution and migration across the world..

There is an alternative explanation which no less confirmed the TOE though. The burials on Gozo are associated with a stone circle and temples of Ġgantija and Santa Verna, so the barrier which isolated this population could be cultural in that the family buried there were from a hereditary priest or guardian caste who married close relatives to preserve their hereditary lineage, in the same way that the Egyptian pharaohs did.

Again we have an incidental confirmation of the Theory of Evolution.

Thank you for sharing!









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