Chromosome as a chronicler: Genetic dating, historical events, and DNA-genealogic temptation

The idea that all modern humans share a recent within the last , years African origin has been proposed and supported on the basis of three observations. Most genetic loci examined to date have 1 shown greater diversity in African populations than in others, 2 placed the first branch between African and all non-African populations in phylogenetic trees, and 3 indicated recent dates for either the molecular coalescence with the exception of some autosomal and X-chromosomal loci or for the time of separation between African and non-African populations. The magnitude of the excess Y chromosome diversity in African populations appears to result from a greater antiquity of African populations rather than a greater long-term effective population size. These observations are most consistent with a recent African origin for all modern humans. For the last 10 years, human population genetics has focused intently on the question of modern human origins. Most geneticists have considered two opposing hypotheses. Both agree that Homo erectus was the first species in our lineage to leave Africa for Europe and Asia—sometime within the last 2 million years—but the models disagree about what happened next.

The father of all men is 340,000 years old

Either your web browser doesn’t support Javascript or it is currently turned off. In the latter case, please turn on Javascript support in your web browser and reload this page. Several authors have proposed haplotype motifs based on site variants at the mitochondrial genome mtDNA and the non-recombining portion of the Y chromosome NRY to trace the genealogies of Jewish people. Here, we analyzed their main approaches and test the feasibility of adopting motifs as ancestry markers through construction of a large database of mtDNA and NRY haplotypes from public genetic genealogical repositories.

For this purpose we compared haplotype composition in individuals of self-reported Jewish ancestry with the rest of European, African or Middle Eastern samples, to test for non-random association of ethno-geographic groups and haplotypes.

Short tandem repeats (STRs) located on the Y chromosome have been analyzed using reference data and dating methods (Wei, Ayub, Xue.

And our DNA also holds clues about the timing of these key events in human evolution. When scientists say that modern humans emerged in Africa about , years ago and began their global spread about 60, years ago, how do they come up with those dates? Traditionally researchers built timelines of human prehistory based on fossils and artifacts, which can be directly dated with methods such as radiocarbon dating and Potassium-argon dating. However, these methods require ancient remains to have certain elements or preservation conditions, and that is not always the case.

Moreover, relevant fossils or artifacts have not been discovered for all milestones in human evolution. Analyzing DNA from present-day and ancient genomes provides a complementary approach for dating evolutionary events. Because certain genetic changes occur at a steady rate per generation, they provide an estimate of the time elapsed. Molecular clocks are becoming more sophisticated, thanks to improved DNA sequencing, analytical tools and a better understanding of the biological processes behind genetic changes.

Mitochondrial Eve and Y Chromosome Adam

Why Y? The Y chromosome is paternally inherited; human males have one while females have none. What is more, the Y chromosome a father passes to his son is, in large measure, an unchanged copy of his own. But small changes called polymorphisms do occur, and this article describes how the correct interpretation of these changes in the Y chromosome, when passed down from generation to generation, can illuminate our understanding of human history.

The estimated coalescence date for the Y chromosome sample is very recent (37 –49 years) and well after the postulated migration of modern man out.

More than 7 billion people live on this planet — members of a single species that originated in one place and migrated all over 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 , and , 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, and , years ago. That agreement makes the new finding especially significant:.

Genetic Adam and Eve did not live too far apart in time

Eriksen, Lynn B. Jorde, Turi E. King, Maarten H. Many studies of human populations have used the male-specific region of the Y chromosome MSY as a marker, but MSY sequence variants have traditionally been subject to ascertainment bias. Also, dating of haplogroups has relied on Y-specific short tandem repeats STRs , involving problems of mutation rate choice, and possible long-term mutation saturation.

Y chromosome shows that Adam was an African. Citation metadata. Author: Ann Gibbons. Date: Oct. 31, From: Science(Vol. , Issue ). Publisher.

In human genetics , the Y-chromosomal most recent common ancestor Y-MRCA , informally known as Y-chromosomal Adam is the most recent common ancestor MRCA from whom all currently living males are descended patrilineally. The term Y-MRCA reflects the fact that the Y chromosomes of all currently living human males are directly derived from the Y chromosome of this remote ancestor.

The analogous concept of the matrilineal most recent common ancestor is known as ” Mitochondrial Eve ” mt-MRCA, named for the matrilineal transmission of mtDNA , the most recent woman from whom all living humans are descended matrilineally. As with “Mitochondrial Eve”, the title of “Y-chromosomal Adam” is not permanently fixed to a single individual, but can advance over the course of human history as paternal lineages become extinct. Estimates of the time when Y-MRCA lived have also shifted as modern knowledge of human ancestry changes.

In , the discovery of a previously unknown Y-chromosomal haplogroup was announced, [1] which resulted in a slight adjustment of the estimated age of the human Y-MRCA. As of , estimates of the age of the Y-MRCA range around , to , years ago, roughly consistent with the emergence of anatomically modern humans. The Y-chromosomal most recent common ancestor is the most recent common ancestor of the Y-chromosomes found in currently living human males.

Due to the definition via the “currently living” population, the identity of a MRCA, and by extension of the human Y-MRCA, is time-dependent it depends on the moment in time intended by the term “currently”. The MRCA of a population may move forward in time as archaic lineages within the population go extinct: once a lineage has died out, it is irretrievably lost.

Chromosome as a chronicler: Genetic dating, historical events, and DNA-genealogic temptation

By Colin Barras. It shows that the last common male ancestor down the paternal line of our species is over twice as old as we thought. One possible explanation is that hundreds of thousands of years ago, modern and archaic humans in central Africa interbred, adding to known examples of interbreeding — with Neanderthals in the Middle East , and with the enigmatic Denisovans somewhere in southeast Asia. Perry, recently deceased, was an African-American who lived in South Carolina. Geneticists can use such samples to work out how we are related to one another.

Hundreds of thousands of people have now had their DNA tested.

Dates for the mitochondrial coalescence time center around , years BP. Two useful estimates have been made for the Y chromosome (Hammer ;.

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Experts question study claiming to pinpoint birthplace of all humans

The Y chromosome right is pretty minimalist compared to the X, but it holds much more history. Mitochondrial DNA, which is inherited only from our mothers, is short and easy to sequence, so researchers have frequently relied on it to study human DNA, both in present populations and in old bones. But as DNA sequencing technology has improved, it has become progressively easier to sequence all the DNA that an individual carries.

If said individual is a male, the resulting sequence will include the Y chromosome, which is inherited only from fathers. With more data in hand, researchers have been able to perform an analysis of the Y chromosome’s history, and they’ve found that its sequence retains the imprint of both the migrations and technological innovations that have featured in humanity’s past.

The dates are compared with estimates from other studies (indicated by the name of the first author), which variously dated the same A2-T node .

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Human history traced via the Y chromosome

Fathers cannot pass on their mtDNA, only the extra genetic information on their Y chromosome. Because mtDNA only comes from the mother, it does not change very much, if at all, from generation to generation. Mutations do occur, but not very often–less frequently than once per people. Therefore, a person’s mtDNA is probably identical to that of his or her direct maternal ancestor a dozen generations ago, and this fact can be used to connect people across decades.

For example, if a particular type of mtDNA was found primarily in Africa, then we could conclude that people from elsewhere in the world who had that type of mtDNA had a maternal ancestor from Africa. Unlike most of our DNA, mitochondrial DNA is not found in our chromosomes or even in the nucleus the central enclosure that contains all of the chromosomes of our cells.

Its dating indicates that it is nearly coeval with lineage Q-FGC characterizing the Anzick-1 Y chromosome (14C dated at kya). However.

Andrews Georgian University, Tbilisi, , Georgia;. It is commonly thought that human genetic diversity in non-African populations was shaped primarily by an out-of-Africa dispersal 50— thousand yr ago kya. Here, we present a study of geographically diverse high-coverage Y chromosome sequences, including newly reported samples. In contrast to demographic reconstructions based on mtDNA, we infer a second strong bottleneck in Y-chromosome lineages dating to the last 10 ky.

We hypothesize that this bottleneck is caused by cultural changes affecting variance of reproductive success among males. Despite the higher per-base-mutation rate of mtDNA, the much greater length of the Y chromosome Chr Y offers the highest genealogical resolution of all non-recombining loci in the human genome.

No, a Mitochondrial “Eve” Is Not the First Female in a Species

Startlingly, it seems to be the case that every human alive today is descended from the same woman, who lived somewhere in or near Ethiopia, probably not more than , years ago. It also seems likely that those of her descendents who left Africa, perhaps as recently as 90, years ago, displaced all of the earlier human populations of Europe and Asia. This essay aims to provide the greatest possible clarity.

When hominid fossils were very few, the fact that older ones generally looked less like us and newer ones looked more like us led to the view that the various human forms distributed in small pockets around the world evolved more or less independently over hundreds of thousands of years into the same animal: us.

Of course, it’s hard to make definitive arguments on these questions because they rely on molecular clock dating estimates, which are notoriously.

Based on the oldest-known remains in the fossil record, we know that anatomically modern humans were present in Africa at about , years ago. From this starting point, our species was poised to expand its range into Asia and Europe, starting around KYA i. Neanderthals and Denisovans share a common ancestral population at about KYA, though it is not yet clear if their common ancestral population left Africa or if their lineages separated in Africa and both groups migrated out independently.

Hominin relationships and approximate divergence times for lineages leading to Neanderthals, Denisovans and modern humans. Rather, they both come from that population of about 10, individuals — the evidence for which and the theological questions it raises we will discuss in upcoming posts. Understanding how humans can have single maternal and paternal ancestors within a genetically diverse population requires us to take a brief excursion into genetics, and specifically how certain forms of DNA are inherited.

In humans, mitochondria are passed down only from mother to child: sperm do not donate mitochondria to the fertilized egg. As a result, mitochondrial DNA is inherited through the maternal lineage only, in contrast to regular chromosomal DNA, which is inherited through both maternal and paternal lineages. A note about pedigree symbols: circles represent females; squares represent males; a horizontal bar connecting them represents a mating; and a vertical bar from a mating is connected to the offspring of that mating.

In the pedigree below, we see a large extended family that shows the inheritance of three mitochondrial variants labeled with different colors. In order to keep the pedigree compact enough to show, the dashed lines indicate matings that connect to one another by wrapping around from one side to the other.

A recent bottleneck of Y chromosome diversity coincides with a global change in culture

Almost every man alive can trace his origins to one man who lived about , years ago, new research suggests. And that ancient man likely shared the planet with the mother of all women. The findings, detailed today Aug. The results overturn earlier research, which suggested that men’s most recent common ancestor lived just 50, to 60, years ago.

Despite their overlap in time, ancient “Adam” and ancient “Eve” probably didn’t even live near each other, let alone mate. Researchers believe that modern humans left Africa between 60, and , years ago, and that the mother of all women likely emerged from East Africa.

Calculating the date of origin for the ancestors of modern Y chromosomes and mitochondrial DNA might seem straightforward: First, simply.

Recently, researchers made waves with the announcement that they had found the mother of all sperm whales: that is, the female from whom all modern sperm whales are descended. The problem is, most people misunderstand exactly what the term means, thinking it means the very first female in a species. By examining 1, sperm whales across the world, researchers surmised that this magnificent matriarch arose sometime in the range of 10,, years ago.

Meanwhile, the fossil record of sperm whales places them back millions of years. Mitochondrial DNA, which is responsible for energy metabolism, is cordoned off from the rest of our DNA, sitting off on its own in its own container. Researchers believe that at some point early in our evolution, the single cell organism that is our oldest ancestor engulfed another bacteria, and eventually the two slowly developed a symbiotic relationship that continues to this day.

That bacteria became the first mitochondria. If you want to go all the way back to the actual biological Eve, you would have to seek out the ancestor of our mitochondria, says Roger Bull, a senior research assistant in the molecular biodiversity lab at the Canadian Museum of Nature. In nearly all multicellular organisms, mitochondrial DNA is passed down the matrilineal line from generation to generation. This fact is extremely handy for researchers, who can use these DNA biomarkers to trace back the matrilineal history of a species.

Alas, while mothers also pass their mitochondrial DNA to males, those sons cannot pass this DNA to their own children.

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