Echoes of the ancestors

I recently finished geneticist Bryan Sykes's book, Saxons, Vikings, and Celts: A Genetic History of Britain and Ireland, which describes the first exhaustive study of the DNA of England, Scotland, Wales, and Ireland.  From there, I jumped right into The Ghosts of Cannae: Hannibal and the Darkest Hour of the Roman Republic, by Robert L. O'Connell, which looks at one of the bloodiest battles on record -- the nearly complete massacre of the Roman army by the Carthaginians at the Battle of Cannae in 216 B.C.E.  That book, like Sykes's, considers the large-scale movements of populations.  The Carthaginians, for example, were mostly displaced Phoenicians who had intermarried with Indigenous North African people, and then occupied what is now Spain, adding in a Celtic strain (the "Celtiberians").

One thing that made my ears perk up in O'Connell's book is that Hannibal, in his march toward Rome, crossed through Transalpine Gaul, picking up large numbers of Gaulish mercenaries along the way, who of course had their own grudge with Rome to settle.  And his path took him right near -- perhaps through -- the valley up in the Alps containing the capital of the Celto-Ligurian tribe called the Tricorii, a town then known as Vapincum.

The name Vapincum eventually was shortened, and morphed into its current name, Gap, a modern town of forty thousand people.

It also happens to be about ten kilometers from the little village where my great-great-grandfather was born.

My last name was, like the name of Gap, altered and shortened over time.  It was originally Ariey, and then picked up a hyphenated modifier indicating the branch of the family we belonged to, and we became Ariey-Bonnet.  When my great-great-grandfather, Jacques Esprit Ariey-Bonnet, came over to the United States, the immigration folks didn't know how to handle a hyphenated name, and told him he'd have to use Ariey as his middle name and Bonnet as his surname, so all four of his children were baptized with the last name Bonnet, despite the fact that it wasn't his actual surname.

Just one of a million stories of how immigrants were forced to alter who they were upon arrival.

In any case, about three years ago, I had my DNA analyzed, and one of the things I found out was about my Y-DNA signature.  This is passed down from father to son, so I have the same Y DNA (barring any mutations) as my paternal ancestors as far back as you can trace.  And it turns out my haplogroup -- the genetic clan my Y-DNA belongs to -- is R1b1b2a1a2d3, which for brevity's sake is sometimes called R1b-L2.  And what I learned is that this DNA signature is "characteristically Italo-Gaulish," according to Eupedia, which is a great source of information for the histories of different DNA groups.

Distribution of the larger R1b Y DNA haplogroup [Image licensed under the Creative Commons Maulucioni, Haplogrupo R1b (ADN-Y), CC BY-SA 4.0]

What's most interesting is that as far back as I've traced my paternal lineage, they hardly moved at all.  My earliest known paternal ancestor, Georges Ariey, was born in about 1560 in Ranguis, France, only about a kilometer from the village of St. Jean-St. Nicolas where my great-great-grandfather Jacques Esprit Ariey-Bonnet was born three hundred years later.  And the DNA I carry indicates they'd been there a lot longer than that.

I have to wonder if my paternal ancestors were some of the Gauls who were there to see Hannibal's army headed for their fateful meeting with the Romans -- or even if they may have joined them.  The Tricorii were apparently noted for going into battle wearing nothing but body paint, so maybe this accounts for my own tendency to run around with as little clothing as is legally permissible when the weather's warm.  What's bred in the bone comes out in the flesh, as John Heywood famously said.

So then I had to look at my mtDNA haplogroup.  The mt (mitochondrial) DNA descends only from the maternal line, so we all have mtDNA from our mother's mother's mother (etc.).  Each person's mtDNA differs from another's only by mutations that have accrued since their last common matrilineal ancestor, and this can provide an idea of how long ago that was (in other words, when the two lineages diverged from each other).  Simply put, more differences = a longer time span since the two shared a common ancestor, making both mtDNA and Y DNA something geneticists call a molecular clock.  The mtDNA from my earliest known maternal ancestor, Marie-Renée Brault, who was born in 1616 in the Loire Valley of western France, belongs to haplogroup H13a1a.  Once again according to Eupedia, this lineage goes back a very long way -- it's been traced to populations living in eastern Anatolia and the Caucasus, and from there spread through the mountains of Greece, across the Alps, and all the way to western France where my maternal great-great (etc.) grandmother lived.

So that genetic signature was carried in the bodies of mothers and daughters along those travels, then crossed the Atlantic to Nova Scotia, then went back across to France when the British expelled the Acadians in the Grand Dérangement, and crossed a third time to southern Louisiana in the late eighteenth century, finally landing in the little town of Raceland where my mother was born.  My dad's Y DNA took a different path -- staying put in the Celto-Ligurian populations of the high Alps for millennia, and only in the nineteenth century jumping across the Atlantic to Louisiana, eventually to meet up with my mother's DNA and produce me.

It's astonishing to me how much we now can figure out about the movement of people whose names and faces are forever lost to history, echoes of our ancestors left behind in our very genes.  However much I'd like to know more about them -- a forlorn hope at best -- at least I've gotten to find out about the shared heritage of our genetic clans, and can content myself with daydreams about what those long-ago people saw, heard, and felt.

****************************************

Written in the genes

Two years ago, I wrote about a mysterious plunge in global average temperature that occurred 12,800 years ago.  It's nicknamed the "Younger Dryas event," after the tundra wildflower Dryas octopetala, which showed a population explosion over the following millennium (as judged by pollen in ice core samples).  This plant only flourishes when the winters are extremely cold, and the pollen spike, along with various other lines of evidence, supports a rapid drop in temperature averaging around six degrees Celsius worldwide.

[Image licensed under the Creative Commons xulescu_g, Dryas octopetala (41907904865), CC BY-SA 2.0]

The obvious question, of course, is what could cause such a rapid and catastrophic drop in temperature.  There are three reasonably plausible answers that have been suggested: 

1. an impact by a comet or meteorite causing an ejection of ash into the atmosphere, blocking sunlight
2. the collapse of an ice dam across what is now the St. Lawrence Seaway -- the temperature had been warming prior to the event -- allowing the emptying of an enormous freshwater lake into the North Atlantic, shutting off the thermohaline circulation and propelling the Northern Hemisphere back into an ice age
3. a nearby supernova in the constellation Vela frying the ozone layer, causing a collapse of ecosystems worldwide and an atmospheric chain reaction resulting in a global drop in temperature

The discussion amongst the scientists is ongoing, but the weight of evidence seems to favor the impact hypothesis.  (The link I posted above has more details, if you're curious.)

What's more certain is that the Younger Dryas event had a massive effect.  A number of large mammal groups -- including mastodons, North American camels, dire wolves, and gomphotheres (a bizarre-looking elephant relative) -- all went extinct shortly after the event itself, whatever it was, occurred.  Humans very nearly bit the dust, too; two of the dominant cultures of the time, the Natufian culture of the Middle East and the Clovis culture of North America, both collapsed right around the same time.

It's the latter that brings the topic up, because of some fascinating new research that came out last week, led by Paula Paz Sepúlveda of the Universidad Nacional de La Plata (Argentina), which looks at the effects this wild climate reversal had on the human genome.

What the researchers did was look at the makeup of the Q Y-DNA haplogroup.  You probably already know that two bits of our genome, the Y chromosome and the mitochondrial DNA, are frequently used for analyzing ethnic group affiliations because they don't recombine each generation -- they're passed down intact through (respectively) the paternal and maternal line.  So your mtDNA is the same as your mother's mother's mother's (etc.), and if you're male, your Y DNA is the same as your father's father's father's (etc.).  This means that the only differences in either one are due to mutations, making them invaluable as a measure of the degree of relatedness of different ethnic groups, not to mention providing a way to track patterns of human migration.

The Q haplogroup is ubiquitous in indigenous people of North and South America, so it was a good place to start looking for clues that the climate shift might have written into the human genome.  And they found them; coincident with the Younger Dryas event there was a marked drop in genetic diversity in the Q haplogroup.  It looks like the climate calamity caused a bottleneck -- a severe reduction in population, resulting in a loss of entire genetic lineages:

The YD impact hypothesis states that fragments of a large disintegrating asteroid/comet hit North America, South America, Europe, and Western Asia at 12,800 cal BP.  Multiple airbursts/impacts produced the YD boundary layer (YDB, Younger Dryas boundary), depositing peak concentrations of a wide variety of impact markers.  The proposed impact event caused major changes in continental drainage patterns, ocean circulation, in temperature and precipitation, large-scale biomass burning, abrupt climate change, abrupt anomalous distribution of plants and animals, extinction of megafauna, as well as, cultural changes and human population decline.  The diversity of the set of markers related to the cosmic impact is found mainly in the Northern hemisphere, including Venezuela, but they have also been recorded in the Southern hemisphere, in Chilean Patagonia, and Antarctica.

It's fascinating to think of our own genomes, and (of course) the genomes of other species, as being a kind of proxy record for climate; that not only gradual fluctuations, but sudden and unexpected events like impacts and volcanic eruptions, can leave their marks on our DNA.  It brings home once again how interlocked everything is.  Our old perception of humans as being some kind of independent entity, separate from everything else on Earth, is profoundly wrong.  We were molded into what we are today by the same forces that created the entire biosphere, and we can't separate ourselves from those forces any more than we could disconnect from our own heartbeats.  As Chief Seattle famously put it, "Man did not weave the web of life, he is merely a strand in it.  Whatever he does to the web, he does to himself."

****************************************