Eva's Daughters: genes, history and geography

Previous article – "Sons of Adam"

"Y-chromosomal Adam" and "mitochondrial Eve" are not at all the married couple from whom modern humanity originated. They were not even the first people of the modern type, and "Adam" lived tens of thousands of years later than "Eve". Why is it from them that we trace our lineage? For about the same reason that the genealogical trees of noble families begin with the most distant ancestors, which can be seen in the darkness of centuries. In fact, "Adam" and "Eve" are not real people, but virtual points from which the branching of the molecular genealogical tree of mankind begins.

Background

In molecular genealogy, as in ordinary genealogy, the origin of entire peoples and individuals can be traced separately along the paternal and maternal lines.

If a man – the carrier of the Y chromosome - does not leave male descendants, the branch of the family tree along the male line breaks off. Inheritance through the female line, through mitochondrial DNA (mtDNA), ends on every boy: the mitochondria received from the mother, which give energy for the rotation of the sperm tail, if they get into the egg, then for some reason they are destroyed. Both men and women receive mitochondria from the cytoplasm of the mother's egg, women pass it on to their daughters, those to their... The female line is completely cut off if a woman does not have daughters or they die before they give birth to girls. So even with a stable population size, when on average each couple has two children living to reproductive age, due to random combinations of the sex of the descendants (two boys, two girls or a boy and a girl), a quarter of the straight lines of sex markers will be interrupted in each generation, in the next - another quarter ... Theoretically after several dozen generations the number of ancestral mtDNA and Y chromosomes will decrease to a vanishingly small amount. Practically, markers of those genera in which such breaks did not occur are preserved in the population – by pure chance or due to rare positive mutations. Genetic diversity is further reduced when, after a drought, flood, hungry winter, etc., only a handful of survivors remain from an entire tribe. The diversity of hereditary markers and the genome of the population as a whole can increase due to strangers accepted into the tribe, and due to random mutations, especially when the population grows – but then famine, war, volcanic eruption or the onset of a glacier happens again… Adam probably had brothers and uncles on his father's side, and Eve had sisters and aunts, but it is impossible to see their traces by sex markers.

Eva's African origin was calculated back in the 1980s. Adam is 10 years later: the number of nucleotide pairs in the Y chromosome is thousands of times greater than in mtDNA, and it is much more difficult to analyze their sequences. In both cases, according to the distribution of marker mutations in DNA samples of tribal representatives, who, according to ethnographic data, are direct descendants of the first settlers in this territory, markers common to all modern peoples were found only in Africa. The tribes remaining in the ancestral homeland of mankind have acquired their markers over thousands of years, and the heirs of those who settled around the world in different ways have their own. According to the frequency of occurrence of these marks in different regions of the planet, it is possible to reconstruct the paths of ancient migrations both in Africa and around the world. And knowing the probability of random mutations allowed us to calculate the lifetime of our common direct ancestors along the female and male lines, 150-200 and 60-80 000 years ago – very approximately and with huge confidence intervals.

Why is Adam so much younger than Eve?

Breaks in inheritance in the male line occur much more often than in the female line. Nature experiments on males more often: if a mutation in the coding part of the genome turns out to be useful, the male will pass it on to the descendants of both sexes, it will be harmful – there will be enough males for the survival of the species without it. The females build nests, keep a fire in the hearth and poke around in the garden. Males hunt mammoths and beat each other on the heads with clubs, and those who are stronger, get themselves harems and drive away predators and other males from them. Therefore, the continuous female lines of our pedigree can be traced much further, and there are more different mtDNA haplogroups preserved than the male ones.

From the creation of the world

Billions of years ago, mitochondria were bacteria that settled in the cells of primitive eukaryotic (having a cell nucleus with linear chromosomes) organisms and took over the work of producing heat and energy for the host. During their life together, they lost some of their genes as unnecessary during their lifetime on everything ready, some were transferred to nuclear chromosomes, and now the double ring of human mtDNA consists of only 16,569 pairs of nucleotide bases. Most of the mitochondrial genome is occupied by 37 genes. Due to the high concentration of oxygen free radicals (byproducts of glucose oxidation) and the weakness of the error recovery mechanism during DNA copying, mutations in mtDNA occur an order of magnitude more often than in nuclear chromosomes. Replacement, loss or addition of one nucleotide here occurs approximately once every 100 generations – about 2500 years. Mutations in mitochondrial genes – disturbances in the work of cellular power plants – are very often the cause of hereditary diseases.

The only function of mitochondria is the oxidation of glucose to carbon dioxide and water and synthesis due to the released energy of cellular fuel – ATP and a universal reducing agent (proton transporter) NADH. (NAD is nicotinamide adenine dinucleotide – try to pronounce it without hesitation). Even for this simple task, dozens of enzymes are needed, but most of the protein genes necessary for the operation and maintenance of mitochondria have long been transferred to the chromosomes of the "host" cells.

Tandem repeats, which are used in male DNA genealogy, are not present in mtDNA, and there are very few meaningless sequences: the genes are located close to each other, separated by inserts of several nucleotides. For molecular genetic studies, the so-called displacement loop is mainly suitable – a non-coding region with a size of 1143 nucleotide pairs. But mutations also occur in it (or rather, they persist, because they practically do not affect the work of mitochondria) even more often, about 1 time in 1000 years. This hypervariable mtDNA section is divided into two segments lying on the sides of the zero point from which the divergence of the mtDNA double helix begins when it is copied. On the segment from 16001 to 16569 nucleotides there is a "low-resolution region", HVR1 (hypervariable region 1), by which you can determine the haplogroup and, if you are lucky, get a little additional information. Deviations from the standard in the high-resolution region (HVR2), in 1-575 nucleotides, are used for detailed analysis. However, for an individual pedigree, it is not possible to trace the relationship on the maternal line as accurately as on the paternal one.

Women's logic

Confusion with the classification in molecular genealogy in the female line began back in 1981, when scientists at the University of Cambridge published the results of the first sequencing – analysis of the sequence of nucleotides – of human mtDNA, obtained under the leadership of Nobel laureate Frederick Sanger (Frederick Sanger). This text of 16569 nucleotides, the Cambridge Standard Sequence (Cambridge Reference Sequence, CRS), was taken as a standard (in 1999 it was clarified – by exactly one letter). Deviations from it are called mutations and are denoted by a combination of numbers (nucleotide numbers) and letters (nucleotide names). For example, 1651C means that the nucleotide number 1651 (in the "standard" CRS is thymine, T) is replaced by cytosine (C), and 315.1C indicates that after the 315th nucleotide, one extra cytosine is inserted into the "standard" chain.

In fact, CRS belongs to haplogroup H – one of the youngest. She is the result of hundreds of mutations of the original sequence that occurred over hundreds of thousands of years, separating "Eve" and an anonymous Englishwoman from the Cambridge maternity hospital, from whose placenta mtDNA was isolated for sequencing. But it is too difficult to change the established classification, it is easier to adapt to the current nomenclature.

mtDNA haplogroups, like Y-chromosomal ones, are designated with Latin letters (this sometimes leads to additional confusion among amateurs when one of the disputants writes about the maternal, and the other about the paternal group). Male haplogroups from A to R are indexed in the order in which the corresponding point mutations appear on the family tree. The oldest females belong to the supergroup L, from L0 to L3, and the relatively late ones, found among the Indians of South America and their Asian relatives, received indexes from A to D. In addition, despite the fact that there is much more room for mutations on the Y chromosome, female haplogroups are much more diverse, and combined indices like CZ and pre-JT have to be introduced for newly identified intermediate groups.

Thousands of years and kilometers

The author of the book "Seven Daughters of Eve", Bryan Sykes (Bryan Sykes) came up with names for the alleged progenitors of most Europeans – Ursula (U), Xenia (X), Elena (H), Velda (V), Tara (T), Catherine (K) and Jasmine (J).

The descendants of "Elena", carriers of the mitochondrial haplogroup H, which already includes more than 30 subgroups, make up the vast majority – about 40% – of the modern population of Europe. Maybe the replacement of just one nucleotide in a non–coding (and in fact – taking part in the regulation of mitochondrial genes) segment is one of the last evolutionary changes in the human genome, which led to the growth of the population of carriers of this haplogroup. In 2005, researchers from the University of Newcastle, led by Professor Patrick Chinnery, found that among patients who had suffered severe bacterial infections, the survival rate among haplogroup H carriers was twice as high as that of representatives of nine other haplogroups.

This is about how the carriers of haplogroup N. traveled around the world.
The migration paths of other mtDNA groups are shown in the following figure.

It is possible to trace and map the main roads along which our great-great-grandmothers roamed in time and space, and calculate the estimated time for each fork – the appearance of a new mutation, from the first "daughters of Eve" to the most recent – haplogroups I and V, which are only about 15,000 years old. But, looking at such a map, it should be taken into account that mtDNA groups spread out on the Ground much wider than Y-chromosomal ones. It would seem that traveling is a man's business, but men returned from them with proceeds or loot, as well as with brides or captives. Many, of course, stayed on the conquered lands, but even the campaigns of Attila and Genghis Khan are trifles compared to the fact that most peoples had a wife moving into her husband's house, and her daughters also married in a neighboring village. As a result, the diversity of female haplogroups in modern populations is several times greater than that of males.

In mass studies, such as the Genography project, only a low-resolution zone, HVR1, is analyzed in mtDNA, which can be used to determine belonging to one of two dozen haplogroups on the maternal side. At the same time, the more common your group is, the more distant relatives you will find in the database. But all DNA samples, both obtained during routine work from "typical natives" and sent by individual participants, have been stored for years and decades, so for a fee those wishing to clarify the details of their molecular genealogy can order additional analyses, narrowing the number of matching haplotypes. However, even a complete coincidence of two people with all markers in both areas of the loop, HVR1 and HVR2, only says that with a probability of 50% their common great-great... maternal grandmother lived about 700 years ago. It is possible to sequence a complete mtDNA sequence and several somatic markers, but this is unlikely to provide additional information about individual genealogy – except in special cases. One of the endless Brazilian TV series revolves around endless DNA tests, and in life everything is much simpler – and much more complicated.

And we are not local...

There are no indigenous peoples in the world. Even carriers of the most ancient Y-chromosomal haplogroup A in modern Africa are now most often found in the north and far to the south from the supposed place of residence of "chromosomal Adam". And its bearers make up the same 45% in the tribes of Bushmen and Hottentots as among the Arabs of Sudan, who differ greatly from them in anthropological data, language and customs. In second place are the Ethiopian tribes of Amhara and Oromo, who live about the same place where our ancestor lived in far from heavenly conditions. And who, for example, are considered native Englishmen? The Iberians, who seem to have migrated to present-day England from the territory of present-day Spain back in the III millennium BC? Celtic tribes, including the Britons, who since about 700 BC took turns crossing the English Channel from now French Brittany and ousting their predecessors from their homes? Descendants of Roman legionnaires or Germanic tribes of Angles, Saxons, Jutes – who else with battles or in a good way moved to the territory of Britain up to the Normans? And by the way, which nationality should they be attributed to – future Frenchmen or former Vikings? Although the latter is a profession, not an ethnic group… But according to archaeological data, people lived in the British Isles until the last ice Age, and with the retreat of the glacier, 16,000 years ago, completely different tribes settled this land again. So all current Britons, like all current peoples, are migrants and mestizos.

Black & white

In recent years, the American descendants of black slaves have become fashionable to look for their historical roots. Black pop stars not so long ago even staged a show on television about this. Among other interesting news for viewers, it turned out that the famous TV presenter Oprah Winfrey comes from the Kpelle tribe in Liberia, and Oscar-winning film actress Whoopi Goldberg hails from Guinea-Bissau. However, Whoopi did not notice a letter transmitted through official diplomatic channels from senior statesmen of a small impoverished African country in a pile of other correspondence. And she has no time to fly to visit her newfound relatives: the show must go on.

In a recent study, it turned out that typically African markers are found in the chromosomes of 30% of Americans who sincerely consider themselves white – greetings to them from the great Ethiopian poet A.S. Pushkin! Let's use his example to analyze some of the difficulties that you can stumble upon, finding out an individual pedigree from DNA.

1/8 of his genes "the sun of Russian poetry" received from Ethiopia and Germany: the poet's great-grandmother, nee Christina-Regina von Scheberch, said: "Shorn shorts make me a shornie repeat ...". Pushkin's grandfather, Osip Abramovich, received half of the Ethiopian genes, including the Y chromosome of Abram Petrovich - most likely one of the African groups, A or B. (Such a haplogroup, transmitted in a direct male line, can certainly be found in the blond residents of Pskov and the surrounding area – the Hannibals lived in Mikhailovsky for a long time). The sons of Sergei Lvovich Pushkin and Nadezhda Osipovna Hannibal (nee Pushkin, but from another branch of the genus), had a quarter of the Ethiopian genes, but they received mtDNA from their mother – certainly one of the European and probably (although not necessarily) haplogroup H. The Y-chromosomal haplogroup they most likely had was the most Slavic, R1a. As Pushkin himself wrote, "We are descended from a Prussian descendant of Radsha or Racha... who left for Russia during the principality of St. Alexander Yaroslavich Nevsky." Pushkin was wrong: Radsha "came from the Germans" a century earlier and, as the Pushkinists established, not "from the Germans", but from Serbia, from the city of Petrovaradin. In Serbia, the East Slavic haplogroup R1a is even more common than in Russia (although I1b is considered typically South Slavic). And if it were "from the Germans", then in Prussia R1a is one of the most common groups: both from a common Indo-European ancestor, and from the Lusatians (Sorbs), who long ago migrated from the Adriatic Sea far to the north. It is quite possible that many Serbs and Croats by the name of Radjic are relatives of Pushkin.

According to sexual markers, it is possible not to detect the presence of "black" genes even in a very black mulatto, if his father's mother and mother's father were Negroes. And in order to find an eighth of African blood in an individual sample, and not in a sufficiently large sample, it is unknown how many thousands of somatic markers need to be sorted out and whether this is possible in principle.

It is better not to start talking about "purity of blood" with experts in the field of ethnogenomics – you can run into rudeness. It is among amateurs that there are lovers of measuring the length and thickness of chromosomes with representatives of other haplogroups, but it is dangerous for racists and nationalists to do DNA analysis: no matter how this causes a crisis of self-identification. Imagine a combination of neo–Nazi ideology, a blond-haired and blue-eyed phenotype, which is determined by somatic chromosomes, and a typically Jewish haplogroup J1 on the paternal side, and on the maternal side - either Asian or Indian mitochondrial group X. Some of its carriers, moving after the retreating glacier, in the steppes east of the Aral Sea turned not to the east, all the way to America, and to the West, having reached back in prehistoric times as far as the Orkney Islands off the coast of Scotland. And an orthodox Jew and Zionist with the picturesque surname Levitan may well find a truly Nordic, seasoned Finno-Ugric male haplogroup N: Ashkenazi Jews have lived in western Europe for a long time…

The study of molecular genealogy is the best way not only to understand that all people are brothers, but also to find additional information for the analysis of personal pedigree. In the database of the Family Tree DNA company, the one that does the analyses for the Genography project, in the spring of 2007 there were over 90,000 Y-DNA test results, more than 41,000 mtDNA analysis records and almost 4,000 family projects. And this is far from the only such database, and access to most of them is open and free or very cheap. However, all studies of the connections of surnames and haplotypes are conducted in Western Europe and North America, and in Russia there is only one such project – the Sychev Family Club. But we still have everything ahead of us.

We thank Anatoly Klesov for his help in writing the article.

Alexander Chubenko
Portal "Eternal youth" www.vechnayamolodost.ru

The journal version of the article was published in Popular Mechanics No. 11-2007

28.11.2007