Friday, December 28, 2012

Who we are, part 1 (Mum)

At last I am able to dilate upon my remote ancestry, thanks to the National Geographic Society’s Geno 2.0 project, which I described earlier. The results of their analysis of my mitochondrial DNA and my Y-chromosome arrived when I was in London a few weeks ago, and I have been gradually absorbing the implications ever since, most of which are simply awe-inspiring. On the whole I am thankful that my mother never lived to be vexed by the idea that it is thanks to her, and her distant relations, that my brothers and I are 2.7% Neanderthal, although my beloved Lyolik says with firmness that he reckons that this figure is far too low. Whichever way you look at it, however, there can be no doubt that approximately 60,000 years ago one or quite possibly more of my mother’s female ancestors turned the head of Hairy Slobodan of the Caucasus, some no doubt fetching Neanderthal, and that this was far more than a brief dalliance; evidently it involved a sustained period of gleefully horizontal folk-dancing in the flickering light of a fire, perhaps in a cave or escarpment, or in the lea of some convenient, mossy bank (for privacy). Intriguing.

Let us go back to the beginning, however. The common direct maternal ancestor to all people living today was born in East Africa around 180,000 years ago. Obviously she was not the only female hominid alive at that remote time, but hers is the only line of posterity that has survived into current generations. This woman represents the deepest root of the human family tree. She gave rise to two descendant lineages known as L0 and L1’2’3’4’5’6, each of which is characterized by a different set of genetic mutations carried by their respective members. Current genetic data indicate that indigenous people belonging to these groups are found exclusively in Africa. This means that, because all humans have in a common this female ancestor, and because Africans are the oldest groups on the planet, we know our species—each and every one of us, the entire human family—originated there. The more historically-minded might choose to think of this as a distant but satisfactory premonition of gins-and-tonic on the verandahs of suburban Nairobi or the polo fields of Happy Valley, but in truth we are looking at hairy hominids busying themselves over tens of thousands of years with the task of basic survival, and the quest for controllable flame—fire! the earliest glimmer of the pre-dawn of human civilization—at around the same vital moment as the earliest discovery, or evolution, or invention of language itself, those guttural love cries with which in due course Mum’s people evidently beguiled certain Neanderthals of the Caucasus.


Eventually, by a process of gradual genetic mutation, L1’2’3’4’5’6 gave rise to L3 in East Africa. While L3 individuals are found all over Africa, L3 is important because of its movements north. Our L3 maternal ancestors were the first party of Homo sapiens to leave Africa, and therefore represent the deepest branches of the tree found outside that continent. Thenceforth, members of this group went in different directions. Many stayed on in Africa, dispersing to the west and south. Some L3 lineages are predominant in many Bantu-speaking groups who originated in west-central Africa, later scattering throughout the continent and spreading this L3 lineage from Mali to South Africa. Today, L3 is also found in many African-Americans. Other L3 individuals, however, our ancestors, kept moving northward, eventually leaving the African continent completely. These people gave rise to two important haplogroups that went on to populate the rest of the world.

It is likely that a fluctuation in climate may have prompted our ancestors’ departure from Africa. The African Ice Age was characterized by drought rather than by cold. Around 60 to 50,000 years ago the ice sheets of northern Europe began to melt, introducing a period of warmer temperatures and moister climate in Africa. Parts of the inhospitable Sahara briefly became habitable. As the drought-ridden desert changed to savanna, the animals our ancestors hunted expanded their range and began moving through the newly emerging green corridor of grasslands. Our nomadic ancestors followed the good weather and plentiful game northward across this Saharan avenue, although the exact route they followed remains to be determined. Whatever the cause of the exodus, it is also clear that when it occurred (a) there were barely 2,000 individuals of the species Homo sapiens left alive, so we very nearly became extinct before the long human migrations even began. We survived only by the skin of our teeth; our civilization might never have developed at all. (b) Those 2,000 shivering, frightened, increasingly desperate specimens were evidently huddled in and around an area of Ethiopia known as the Asaf Depression. And that was the point of departure for many tiny groups of the survivors, of whom a handful actually stayed put.


Our next crucial maternal ancestor is the woman whose descendants formed haplogroup N. Haplogroup N comprises one of two groups that were created by the descendants of L3. One of these two groups of individuals moved north rather than east and left the African continent across the Sinai Peninsula, in what is now Egypt. Also faced with the harsh desert conditions of the Sahara, these people apparently followed the Nile basin, which yielded a reliable supply of food and water in spite of the surrounding desert and its frequent sandstorms. Descendants of these migrants eventually formed haplogroup N. Early members of this group lived in the eastern Mediterranean region and western Asia, where they apparently co-existed for a time with other hominids such as Neanderthals. Excavations in the Kebara Cave (Mount Carmel) in Israel have unearthed Neanderthal skeletons as recent as 60,000 years old, indicating that there was both ample geographical and chronological overlap between us and them. This accounts for the presence of Neanderthal DNA in those of us who live outside Africa—between 1% and 4% of the whole of our DNA is Neanderthal.

Be that as it may, after several thousand years in the Near East, members of our group began moving into unexplored neighboring territories, following large herds of migrating game across vast plains. These groups broke into several directions and made their way into territories surrounding the Near East. Today, haplogroup N individuals who headed west are prevalent in Turkey and the eastern Mediterranean. They are found farther east in parts of Central Asia and the Indus Valley of Pakistan and India. And members of our haplogroup who headed north out of the Levant across the Caucasus Mountains have remained in southeastern Europe and the Balkans. Importantly, descendants of these people eventually went on to populate the rest of Europe, and today comprise the most frequent mitochondrial lineages found there.


After several thousand years in the Near East, individuals belonging to a new group called haplogroup R began to move out and explore the surrounding areas. Some moved south, migrating back into northern Africa. Others went west across Anatolia (roughly corresponding with modern Turkey) and north across the Caucasus Mountains of Georgia and southern Russia. Still others headed east into the Middle East, and on to Central Asia. All of these individuals had one thing in common: they shared a female ancestor from the N clan, a recent descendant of the migration out of Africa.

The story of haplogroup R is complicated, however, because these individuals can be found almost everywhere, and because their origin is quite ancient. In fact, the ancestor of haplogroup R lived relatively soon after humans moved out of Africa during the second wave, and her descendants undertook many of the same migrations as her own group, N. Because the two groups lived side by side for thousands of years, it is likely that the migrations radiating out from the Near East comprised individuals from both of these groups. They simply moved together, bringing their N and R lineages to the same places around the same times. The tapestry of genetic lines became quickly entangled, and geneticists are currently working to unravel the different stories of haplogroups N and R, since they are found in many of the same far-flung regions.


Descending from the R group, a woman gave rise to people who now constitute haplogroup U. Because of the great genetic diversity found in haplogroup U, it is likely that this woman lived around 47,000 years ago. Let us call her Granny Ugh! Her descendants gave rise to several different subgroups, some of which exhibit very specific geographic homelands. The very old age of these subgroups has led to a wide distribution; today they harbor numerous particular European, northern African, and Indian components, and are to be found in Arabia, the northern Caucasus Mountains, and throughout the Middle and Near East.

One interesting subgroup is U6, which branched off from haplogroup R while still in the Middle East, moved southward, and today is found in parts of northern Africa. Today, U6 individuals are found in around 10% of people living in North Africa. However, other members of the larger haplogroup U descend from a group that moved northward out of the Near East. These women crossed the rugged Caucasus Mountains in southern Russia, and moved on to the steppes of the Black Sea. These individuals represent movements from the Black Sea steppes west into regions that comprise the present-day Baltic States and western Eurasia. This grassland then served as the springboard for subsequent movements north and west.

Today, this line is part of populations in Europe, West Asia (including Arabia), North Africa, India, and the North Caucasus Mountains. In Europe, this lineage averages 7% of the population. In Scandinavian countries (Norway, Sweden, the Netherlands, etc.) it is between 9% and 16% of the population. In England, it is about 12% of the population. Toward the Mediterranean, this line is between 10% and 12% of the population in Croatia and Greece.


The most recent common ancestor for all of us U5 individuals broke off from the rest of the group and headed north into Scandinavia. Even though U5 is descended from an ancestor in haplogroup U, it is also exceedingly ancient, and thought to be around 30,000 years old.

U5 is quite restricted in its variation to Scandinavia, and particularly to Finland. This is probably the result of the significant geographical, linguistic, and cultural isolation of the Finnish populations, which restricted geographic distribution of this subgroup and kept it genetically isolated. The Saami, reindeer hunters who follow the herds from Siberia to Scandinavia each season, have the U5 lineage at a very high frequency of around 50%, indicating that it may have been introduced during their movements into these northern territories.

The U5 lineage is found outside Scandinavia, though at much lower frequencies and at lower genetic diversity. Interestingly, the U5 lineage found in the Saami has also been found in some North African Berber populations in Morocco, Senegal, and Algeria. Finding similar genetic lineages in populations living thousands of miles apart is certainly unexpected, and is likely the result of re-expansions that occurred after the last glacial maximum around 15,000 years ago. Humans who had been confined to narrow patches in southern Europe began to move outward again, re-colonizing ancient territories and bringing new genetic lineages with them.

In addition to being present in some parts of North Africa, U5 individuals also live sporadically in the Near East at 2%—about one-fifth as frequent as in parts of Europe—and are completely absent from Arabia. Their distribution in the Near East is largely confined to surrounding populations, such as Turks, Kurds, Armenians, and Egyptians. Because these individuals contain lineages that first evolved in Europe, their presence in the Near East is the result of a back-migration of people who left northern Europe and headed south, as though retracing the migratory paths of their own ancestors.


Today, this line is present most often in Finland (15%) and Latvia (12%). It is between 6% and 9% of maternal lineages in Luxembourg, Northern Ireland, Spain, and Slovenia. It is widespread in western Eurasia, particularly to the north. This spread began with the expansion of haplogroup U5B-bearing populations out of West Asia during the Upper Paleolithic, prior to 12,000 years ago, and like other branches of U it reached Europe during the Paleolithic. Despite later waves of migrants from other lineages, it remains common there.

Insomma, we can now conclude (not very surprisingly) that Mum’s distant relations down to approximately 10,000 years ago were only 45% Northern European, and that that component of our ancestry is found at the highest frequency in Britain, Denmark, Finland, Russia and Germany (oh!). While not limited to these groups, it is found at significantly lower frequencies throughout the rest of Europe. This component is probably the signal of the earliest hunter-gatherer inhabitants of Europe, who were the last to make the transition to agriculture as it moved in from the Middle East during the Neolithic period around 8,000 years ago—Hairy Grandmother Margaret on her wee Shetland pony, as Hamish rightly predicted, galloping headlong across the land bridge into the vastnesses of the Scottish highlands at almost the very earliest time that this was possible. Is it any wonder therefore that on my first visit to Edinburgh some years ago I had the strongest feeling that I had been there before?

On the other hand we of the line of U5B are also 37% Mediterranean, a component to be found at the highest frequencies in southern Europe and the Levant—people from Sardinia, Italy, Greece, Lebanon, Egypt and Tunisia. While not limited to these groups, it is found at lower frequencies throughout the rest of Europe, the Middle East, Central and South Asia. This component is also probably a sign of the Neolithic population expansion from the Middle East, beginning around 8,000 years ago, likely from the western part of the Fertile Crescent.

We are also 17% Southwest Asian. This component of our ancestry is found at highest frequencies in India and neighboring populations, including Tajikistan and Iran—and it is probably just as well that Mum never lived to learn this, although I am quite sure that she would have looked askance with her customary pursed-lip skepticism. Nevertheless this component is an undeniable fact of our mitochondrial DNA, and it is also found at significantly lower frequencies in Europe and North Africa. As with our Mediterranean component, it was most probably spread during the Neolithic expansion, perhaps from the eastern part of the Fertile Crescent. Individuals with heavy European influence in their ancestry will show traces of this because all Europeans have mixed with people from Southwest Asia over tens of thousands of years, something that was not lost on Grandfather Borthwick and his slightly crude allegation that there was, at least in the Borthwick line, a “touch of the tar-brush.” Putting it in a slightly more positive light, Mum carried a modicum of the culture of primitive near-eastern philosophy, mathematics, jurisprudence, and the root of writing itself, and no doubt this expressed itself in the skills she duly brought to The Times cryptic crossword puzzle, and to the bridge table. 

For all of this we must be grateful, and now to Dad and the Y-chromosome.

1 comment: