Genghis Khan's genetic legacy has competition

The Mongolian leader left a strong footprint in the Y chromosomes of modern descendants — but he was not the only one.

Millions of men bear the genetic legacy of Genghis Khan, the famously fertile Mongolian ruler who died in 1227. Researchers have now recognized ten other men whose fecundity has left a lasting impression on present-day populations. The team's study1 points to sociopolitical factors that foster such lineages, but the identities of the men who left their genetic stamp remains unknown.

The case for Genghis Khan’s genetic legacy is strong, if circumstantial. A 2003 paper2 led by Chris Tyler-Smith, an evolutionary geneticist now at the Wellcome Trust Sanger Institute in Hinxton, UK, discovered that 8% of men in 16 populations spanning Asia (and 0.5% of men worldwide) shared nearly identical Y-chromosome sequences. The variation that did exist in their DNA suggested that the lineage began around 1,000 years ago in Mongolia.

Genghis Khan is reputed to have sired hundreds of children. But a Y-chromosome lineage traces a single paternal line in a much larger family tree, and for it to leave a lasting legacy takes multiple generations who fan out over a wide geographical area, says Mark Jobling, a geneticist at the University of Leicester, UK, who led the latest study with geneticist Patricia Balaresque of Paul Sabatier University in Toulouse, France.

“Lots of men have lots of sons, by chance. But what normally doesn’t happen is the sons have a high probability of having lots of sons themselves. You have to have a reinforcing effect,” says Jobling. Establishment of such successful lineages often depends on social systems that allow powerful men to father children with multitudes of women.

The start of something big

In addition to Genghis Khan and his male descendants, researchers have previously identified the founders of two other highly successful Y-chromosome lineages: one that began in China with Giocangga, a ruler who died in 15823 whose lineage was spread by the Qing Dynasty, and another belonging to the medieval Uí Néill dynasty in Ireland4.

Jobling’s team made a systematic search for genetic founders by analysing the Y chromosomes of more than 5,000 men from 127 populations spanning Asia; they focused on that region because lots of data were available and there was already evidence of such lineages. The team identified 11 Y-chromosome sequences that were each shared by more than 20 of the 5,321 genomes. The researchers used DNA differences in the shared sequences, which accumulate over time from random mutations, to determine approximately when the founder of the lineage lived. They tracked back the geographical origins of the lineages by assuming that the founding men had lived in the regions where their genotypes were most prevalent and diverse.

Genghis Khan’s paternal lineage again stood out, as did Giocangga’s, Jobling’s team reports in the European Journal of Human Genetics1. The other nine lineages originated throughout Asia, from the Middle East to southeast Asia, dating to between 2100 bc and ad 700. Jobling warns that these dates come with huge margins of error, but he notes that the estimates for the lineages attributed to Khan and Giocangga are very close to those of past studies.

Legacy of power

The founders who lived between 2100 bc and 300 bc existed in both sedentary agricultural societies and nomadic cultures in the Middle East, India, southeast Asia and central Asia. Their dates coincide with the emergence of hierarchical, authoritarian societies in Asia during the Bronze Age, such as the Babylonians. Three lineages dating to more recent times were all linked to nomadic groups in northeast China and Mongolia. These included the lineages linked to Genghis Khan and Giocangga, plus a third line dating to around ad 850.

All three lineages seem to have expanded westwards, possibly along the Silk Road trade route. Historians have documented a series of polities based in inner Asia between 200 bc and the eighteenth century, such as the Qing Dynasty. Jobling says that these civilizations could have fostered dominant male lineages after the sons of a fecund founder decamped to satellite outposts, where they, in turn, fathered powerful descendants.

The researchers identify several candidates for the lineage dating to ad 850, but say that more research is needed. Recovering DNA from the candidate or a long-dead descendant would be the ultimate proof.

“Looking for these links is fascinating. When we did it, we were using pretty indirect lines of reasoning, and you could try and do that with each of these lineages,” says Tyler-Smith. “What I really hope is that at some point someone will find Genghis Khan's tomb and remains.”
_________________
Reference:

Callaway, Ewen. 2015. “Genghis Khan's genetic legacy has competition”. Nature. Posted: January 30, 2015. Available online: http://www.nature.com/news/genghis-khan-s-genetic-legacy-has-competition-1.16767

Article References:

1. Balaresque, P. et al. Eur. J. Hum. Genet. http://dx.doi.org/10.1038/ejhg.2014.285 (2015). 2. Zerjal, T. et al. Am. J. Hum. Genet. 72, 717–721 (2003). 3. Xue, Y. et al. Am. J. Hum. Genet. 77, 1112–1116 (2005). 4. Moore, L. T., McEvoy, B., Cape, E., Simms, K. & Bradley, D. G. Am. J. Hum. Genet. 78, 334–338 (2006).

The when and where of the Y: Research on Y chromosomes finds new clues about human ancestry

First full-chromosome sequencing effort shows most recent male & female common ancestors lived around the same time

More than 7 billion people live on this planet – members of a single species that originated in one place and migrated all over the Earth over tens of thousands of years.

But even though we all trace our family lineage to a few common ancestors, scientists still don't know exactly when and how those few ancestors started to give rise to the incredible diversity of today's population.

A brand-new finding, made using advanced analysis of DNA from all over the world, sheds new light on this mystery. By studying the DNA sequence of Y chromosomes of men from many different populations, scientists have determined that their male most recent common ancestor (MRCA) lived sometime between 120,000 and 156,000 years ago.

It's the first time the human ancestry has been traced back through the male line by sequencing the DNA of many entire Y chromosomes.

And, it agrees reasonably well with previous findings about our female most recent common ancestor, made by studying DNA carried down through the human race's female line. Such studies used DNA from mitochrondria -- structures inside cells – and placed that time of the most recent common ancestor between 99,000 and 148,000 years ago. That agreement makes the new finding especially significant:

The research was done by a team of scientists from Stanford University, the University of Michigan Medical School, Stony Brook University, and their colleagues, and is published in the journal Science.

The team hopes their work will lead to further research on Y chromosomes as vehicles for studying human history – and tracing male lineages back to the common "Adam" ancestors.

Jeffrey Kidd, Ph.D., an Assistant Professor of Human Genetics and Computational Medicine & Bioinformatics who worked on the new study, notes that only recently has it become possible to sequence Y chromosomes, because of technical limitations of previous approaches.

The new paper details how the team was able to make reliable measurements of the sequence variation along the Y chromosome – which is handed down only from father to son without exchanging, or recombining, genetic material with other chromosomes.

Kidd notes that this initial paper on Y chromosome sequence diversity provides important first evidence that the male most recent common ancestor did not live more recently than the female most recent common ancestor.

"We're interested in understanding the historical relationships between many different human populations, and the migration patterns that have led to the peopling of the world," he says. "We hope that others will make use of this approach and sequence additional chromosomes of interest that are related to the peopling of specific places."

The study involved Y chromosomes obtained through the Human Genome Diversity Project, and from other sources. It included chromosomes from 69 men in several populations in sub-Saharan Africa, and from Siberia, Cambodia, Pakistan, Algeria and Mexico.

The great migrations of our ancestors out of Africa, across Asian and Europe and into the Americas all helped shape today's populations – as did more recent forces related to colonialism and ever-growing global mobility.

Genetic studies such as this one may help anthropologists understand those migrations – and their timing – even better by giving them a genetic "clock" to use when studying today's humans, or potentially DNA extracted from ancient bones. It may also help scientists understand the great genetic diversity seen across Africa, and the evolution process that led to modern humans.

The reconciliation of the timing of "Adam" and "Eve", however, may be this study's most important immediate implication.

"This has been a conundrum in human genetics for a long time," said Carlos D. Bustamante, PhD, a professor of genetics at Stanford and senior author of the study. "Previous research has indicated that the male MRCA lived much more recently than the female MRCA. But now our research shows that there's no discrepancy. In fact, if anything, the Y chromosome may be a bit older."
__________________________
References:

EurekAlert. 2013. “The when and where of the Y: Research on Y chromosomes finds new clues about human ancestry”. EurekAlert. Posted: August 1, 2013. Available online: http://www.eurekalert.org/pub_releases/2013-08/uomh-twa080113.php

Human Y chromosome much older than previously thought

A newly discovered Y chromosome places the most recent common ancestor for the Y chromosome lineage more 100,000 years before the oldest known anatomically modern human fossils

UA geneticists have discovered the oldest known genetic branch of the human Y chromosome – the hereditary factor determining male sex.

The new divergent lineage, which was found in an individual who submitted his DNA to Family Tree DNA, a company specializing in DNA analysis to trace family roots, branched from the Y chromosome tree before the first appearance of anatomically modern humans in the fossil record.

The results are published in the American Journal of Human Genetics: http://www.cell.com/AJHG/abstract/S0002-9297(13)00073-6

"Our analysis indicates this lineage diverged from previously known Y chromosomes about 300,000 ago, a time when anatomically modern humans had not yet evolved," said Michael Hammer, an associate professor in the University of Arizona's department of ecology and evolutionary biology and a research scientist at the UA's Arizona Research Labs. "This pushes back the time the last common Y chromosome ancestor lived by almost 70 percent."

Unlike the other human chromosomes, the majority of the Y chromosome does not exchange genetic material with other chromosomes, which makes it simpler to trace ancestral relationships among contemporary lineages. If two Y chromosomes carry the same mutation, it is because they share a common paternal ancestor at some point in the past. The more mutations that differ between two Y chromosomes the farther back in time the common ancestor lived.

Originally, a DNA sample obtained from an African American living in South Carolina was submitted to the National Geographic Genographic Project. When none of the genetic markers used to assign lineages to known Y chromosome groupings were found, the DNA sample was sent to Family Tree DNA for sequencing. Fernando Mendez, a postdoctoral researcher in Hammer's lab, led the effort to analyze the DNA sequence, which included more than 240,000 base pairs of the Y chromosome.

Hammer said "the most striking feature of this research is that a consumer genetic testing company identified a lineage that didn't fit anywhere on the existing Y chromosome tree, even though the tree had been constructed based on perhaps a half-million individuals or more. Nobody expected to find anything like this."

About 300,000 years ago falls around the time the Neanderthals are believed to have split from the ancestral human lineage. It was not until more than 100,000 years later that anatomically modern humans appear in the fossil record. They differ from the more archaic forms by a more lightly built skeleton, a smaller face tucked under a high forehead, the absence of a cranial ridge and smaller chins.

Hammer said the newly discovered Y chromosome variation is extremely rare. Through large database searches, his team eventually was able to find a similar chromosome in the Mbo, a population living in a tiny area of western Cameroon in sub-Saharan Africa.

"This was surprising because previously the most diverged branches of the Y chromosome were found in traditional hunter-gatherer populations such as Pygmies and the click-speaking KhoeSan, who are considered to be the most diverged human populations living today."

"Instead, the sample matched the Y chromosome DNA of 11 men, who all came from a very small region of western Cameroon," Hammer said. "And the sequences of those individuals are variable, so it's not like they all descended from the same grandfather."

Hammer cautions against popular concepts of "mitochondrial Eve" or "Y chromosome Adam" that suggest all of humankind descended from exactly one pair of humans that lived at a certain point in human evolution.

"There has been too much emphasis on this in the past," he said. "It is a misconception that the genealogy of a single genetic region reflects population divergence. Instead, our results suggest that there are pockets of genetically isolated communities that together preserve a great deal of human diversity."

Still, Hammer said, "It is likely that other divergent lineages will be found, whether in Africa or among African-Americans in the U.S. and that some of these may further increase the age of the Y chromosome tree."

He added: "There has been a lot of hype with people trying to trace their Y chromosome to different tribes, but this individual from South Carolina can say he did it."
__________________________
References:

EurekAlert. 2013. “Human Y chromosome much older than previously thought”. EurekAlert. Posted: March 4, 2013. Available online: http://www.eurekalert.org/pub_releases/2013-03/uoa-hyc030413.php