Twigstats: New tool reveals hi-res genetic view of people’s ancestors Premium

Unlocking ancient genetic secrets through prehistoric burials, mass graves, and war graves worldwide reveals population dynamics and migrations.

Prehistoric human ceremonial burials, mass grave mounts, and war graves scattered around the world are a treasure trove of ancient genetic material that scientists consider key to unlocking secrets from our past. The ancient DNA (aDNA) at these sites opens windows into population dynamics, including the expansion and replacement of populations using peaceful, natural or violent means, admixture events involving two or more sub-populations, cultural transitions, migrations for hunting, and wealth at individual, local, and global scales.

This said, tracing genetic ancestry in particular across populations still remains a challenging task. This is because populations across geographical regions often tend to be very similar, statistically speaking.

For example, studies in the past have documented genetic differences between ancient groups such as the hunter-gatherers, early farmers, and the steppe-pastoralists of the Stone and Bronze Ages. Similarly, numerous studies in recent years have provided insights into the genetic diversity of mediaeval populations across the world. But comparing the genetic ancestry of ancient and medieval populations has been hampered by differences in sample sizes. There are fewer samples bearing aDNA, resulting in lower sequencing quality compared to that of medieval or modern genomes, which come from larger cohorts.

The incorporation of genetic material in the form of gene flows laterally, from an ancient line into a modern one after ancient times, adds an additional layer of complexity.

Traditionally, researchers’ studies of aDNA have involved analysing single nucleotide polymorphisms (SNPs), which are natural genetic variations in the genomes. The method has been extensively used to reconstruct genetic histories and ancestry models using aDNA derived from Indo-European and Native American populations.

In a 2009 study, researchers from the Broad Institute in the US and the CSIR-Centre for Cellular and Molecular Biology, Hyderabad, reconstructed India’s population history as well. They analysed 25 diverse groups and identified two ancient populations in the country that were ancestral to most Indians. Ancestral North Indians were found to be genetically closer to Central Asian, European, and Middle Eastern populations while Ancestral South Indians were a distinct group. The analysis of SNPs is a powerful technique when the task is to understand populations, but it’s restricted by the need for high quality DNA samples and its inability to resolve the histories of groups with closely related ancestors.

Alternatively, analytical methods that use haplotypes, or shared segments of DNA, and rare variants instead of only SNPs have been found to be more powerful. Researchers have applied the genealogical tree inference method to modern and ancient genomes to understand their population structure, demographics, locations of ancestors, etc.